Electromagnetic compression method for self-repairing of cable joint insulation using heat-responsive microcapsules

Abstract

The application discloses a cable joint insulation self-repairing electromagnetic compression method using heat-responsive microcapsules, and relates to the technical field of cable electromagnetic compression. In view of the problem that micro-damage is easily caused to the main insulation of a cable in a traditional electromagnetic compression process and cannot be effectively repaired, an axial flow guide groove is processed on the inner wall of a compression pipe, and a self-repairing layer containing heat-responsive microcapsules is arranged between the insulation layer of the cable and the compression pipe; by establishing an electric-magnetic-thermal-force multi-physical field coupling finite element model and a microcapsule rupture behavior model, the parameters of the microcapsules and the discharge parameters of a pulse power source are determined; during electromagnetic compression, the inherent Joule heat and radial extrusion force of the compression process are used to trigger controllable rupture of the microcapsules, insulation repair agents fill insulation defects under the action of the extrusion force and the capillary action of the flow guide groove, and the insulation repair layer is formed by solidification. The application synchronously completes compression and insulation repair, does not need an additional process, and significantly improves the insulation performance and long-term operation reliability of the cable joint.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic crimping technology for cables, and specifically to a self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules. Background Technology

[0002] Cable joints are key components in power transmission lines, enabling cable connections. Their insulation performance and reliability directly determine the operational safety and service life of the line. Currently, medium and high voltage cable joints typically employ electromagnetic crimping technology for conductor connection. This technology utilizes a pulsed electromagnetic field to induce eddy currents in the crimping tube, generating a strong Lorentz force that drives the crimping tube to contract radially at high speed. It offers significant advantages such as fast forming speed, a dense and gapless crimping interface, and high mechanical connection strength. [1] .

[0003] However, during electromagnetic crimping, the instantaneous high temperature and drastic deformation of the crimping tube can easily cause invisible microscopic insulation damage to the cable's main insulation, such as interface microcracks, insulation scratches, and stress concentration at the indentation. During long-term operation, these microscopic defects, under the coupled effects of electric field, thermal field, and moisture, can easily develop into partial discharge, leading to insulation deterioration or even breakdown. [2] This has become a key technical bottleneck restricting the long-term reliability of cable joints. Traditional processes lack effective methods to repair the micro-damage to insulation generated during crimping; engineers can only rely on partial discharge testing. [3] Analyzing crimping defect types offline cannot effectively repair damage at its root.

[0004] Although self-healing microcapsule technology has been applied in the field of composite materials, its introduction into the extreme transient process of electromagnetic pressing faces new challenges: the timing, spatial distribution and degree of rupture of microcapsules under the coupling of multiple physical fields of electro-thermal-mechanical fields are difficult to be directly observed and controlled through conventional experiments, resulting in unpredictable repair effects.

[0005] Therefore, there is an urgent need for a method that can accurately predict and control the rupture behavior of microcapsules in order to achieve in-situ self-repair of insulation damage.

[0006] References: [1]Z Changle Y ,Yuanda Z ,Hui Z , et al.Design of electromagneticpulse crimping device[J].OPTOELECTRONIC MATERIALS AND DEVICES (ICOMD 2020),2021,11767.

[0007] [2] Wang Junbo, Zhan Qinghua, Zhang Weizhong, et al. Study on partial discharge characteristics of typical process defects of cold shrink joint of 10kV XLPE cable [J]. Insulating Materials, 2014, 47(06):61-64.

[0008] [3] Ming Ruiqing. High-frequency pulse current detection analysis of typical partial discharge fault model of 10kV cold shrink cable head [J]. Electronic World, 2019, (22): 20-22. Summary of the Invention

[0009] The purpose of this invention is to provide a self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules. By pre-placing thermally responsive microcapsules between the cable and the crimping tube, and using multi-physics coupled finite element simulation (EMF) to accurately simulate and optimize the rupture behavior of the microcapsules during the transient crimping process, this method addresses the technical bottleneck of easily causing and being unable to repair microscopic damage to the main cable insulation during electromagnetic crimping, from the perspective of material response and structural synergy. This achieves controllable rupture of the microcapsules. The electromagnetic crimping method utilizes the inherent Joule heating and electromagnetic force of the crimping process as triggering conditions, causing the simulation-optimized microcapsules to rupture precisely and controllably, releasing the insulating repair agent. The repair agent is guided by a pre-set flow channel to uniformly fill interface defects, and after crimping, it solidifies to form an insulating repair layer. This ensures efficient electromagnetic crimping and a dense, gapless cable joint area, while simultaneously achieving in-situ self-repair of cable insulation damage, forming a reliable insulation reinforcement interface. This significantly improves the partial discharge initiation voltage and long-term operational reliability of the cable joint, meeting the stringent requirements of power cable lines for cable joint insulation quality. To achieve the above objectives, in a first aspect, the present invention provides a self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules, comprising the following steps: Step 1: Pre-treat the ends of the cable to be crimped; Step 2: Use laser etching to process axially distributed guide grooves on the inner wall of the crimping tube; Step 3: Determine the parameters of the self-healing layer and the thermally responsive microcapsules according to the specifications of the cable joint crimping. Step 4: Based on the parameters obtained in Step 3, prepare thermally responsive microcapsules; coat the microcapsules in powder form or premixed into a silicone grease carrier evenly on the inner wall of the press-fit tube to form a self-healing layer; Step 5: Place the ends of the two cable connectors to be crimped together, and then put the crimping tube over the outside of the cable connector connection. Step 6: Place the electromagnetic coil outside the pressure tube and connect it to the pulse power supply via a switch. Set the discharge voltage and discharge energy of the pulse power supply. The control switch energizes the electromagnetic coil, and the crimping tube contracts radially and presses the cable under the action of the electromagnetic field. This triggers the controlled rupture of the thermal response microcapsule, releasing the insulation repair agent. Under the guidance of the squeezing action and the capillary action of the guide groove, the repair agent extends and covers the cable insulation break, uniformly filling the interface gap between the cable insulation layer and the crimping tube, as well as the cracks on the surface of the insulation layer and the end face of the insulation break. Step 7: Cool the crimped pipe to allow the insulating repair agent to cure and form an insulating repair layer; Step 8: Remove the electromagnetic coil, and conduct a visual inspection and insulation performance test on the finished cable crimped product. If it passes the test, the electromagnetic crimping of the cable joint is complete.

[0010] Preferably, in step 2, the guide grooves on the inner wall of the pressure pipe are axially distributed, with a groove depth of 0.2 mm to 0.5 mm and a groove width of 0.5 mm to 1 mm.

[0011] Preferably, in step 3, an electro-magnetic-thermal-mechanical multi-physics coupled finite element model and a thermal response microcapsule rupture behavior model are established to simulate the thermal-mechanical coupled rupture behavior of microcapsules. Based on the insulation requirements of cable joint crimping, the melting temperature window and particle size of the microcapsule shell, as well as the discharge voltage and discharge energy of the capacitive pulse power supply, are determined.

[0012] Preferably, in step 3, the melting temperature of the thermally responsive microcapsule shell is 90°C to 110°C, and the shell material is polyurea-formaldehyde resin or polymethyl methacrylate.

[0013] Preferably, in step 3, the particle size of the thermally responsive microcapsules is 50 μm to 200 μm.

[0014] Thermoresponsive microcapsules come in two types: one encapsulates an epoxy resin component, and the other encapsulates a curing agent component. The two types of thermoresponsive microcapsules are uniformly mixed and distributed in the self-healing layer.

[0015] Preferably, in step 4, the thermally responsive microcapsules are applied directly in powder form or premixed into the silicone grease carrier and then uniformly coated on the outer surface of the insulating layer and the inner wall of the compression fitting to form a self-healing layer.

[0016] Preferably, in step 5, the discharge voltage of the capacitor pulse power supply is 15kV to 25kV, and the discharge energy is 100kJ to 200kJ.

[0017] Preferably, in step 6, the local instantaneous temperature at the contact interface between the pressure tube and the self-modifying layer is 120°C to 180°C, ensuring that the microcapsule shell is completely softened and ruptured and the repair agent flows effectively, thereby achieving controllable rupture of the microcapsule.

[0018] Preferably, in step 7, the dielectric strength of the cured insulating repair layer is not less than 30 kV / mm, and the volume resistivity is not less than 10 kV / mm.15 Ω·cm.

[0019] Secondly, the present invention provides a cable joint insulation self-healing electromagnetic crimping device, comprising a crimping tube, a self-healing layer, an electromagnetic coil, and a capacitive pulse power supply.

[0020] The inner wall of the press-fit tube is provided with an axially distributed flow guide groove structure; the press-fit tube is configured to radially contract under the action of the pulsed electromagnetic field generated by the energization of the electromagnetic coil; The self-healing layer is disposed between the cable insulation layer and the crimping tube, and the self-healing layer contains thermally responsive microcapsules; The thermally responsive microcapsules are configured to rupture controllably and release an insulating repair agent under the thermal and mechanical coupling effect generated by electromagnetic crimping. The insulating repair agent can flow along the flow channel structure to fill the interface gap between the cable insulation layer and the crimping tube, as well as the cracks on the surface of the insulation layer and the end face of the insulation break. After cooling and solidification, an insulating repair layer is formed, so that the crimping tube and the cable insulation layer form a tight bond through the insulating repair layer. The electromagnetic coil is sleeved on the outside of the pressure tube and connected to the capacitive pulse power supply via a discharge switch.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: 1) Accurate prediction and quantitative control of thermally responsive microcapsule rupture behavior were achieved. By establishing a multi-physics coupled finite element model of electro-magnetism-thermal-mechanical fields and a thermally responsive microcapsule rupture behavior model, the rupture state variables of microcapsules under thermo-mechanical coupling were proposed and defined for the first time. This enabled accurate prediction and visualization of the rupture timing, rupture range, and rupture degree of microcapsules during the press-fit transient process, and precise determination of the melting temperature window of the microcapsule shell. This provides scientific theoretical guidance and quantitative design methods for the material selection, structural parameter design, and discharge process parameter matching of thermally responsive microcapsules, ensuring that the microcapsules achieve controllable rupture during the press-fit process.

[0022] 2) In-situ synchronous self-repair of cable insulation micro-damage is achieved. By pre-placing simulated and optimized thermal response microcapsules between the cable insulation layer and the crimping tube, the inherent Joule heat and radial extrusion pressure of the electromagnetic crimping process are used as dual triggering conditions. The microcapsules rupture precisely and release the insulation repair agent while being crimped, without the need for additional heating or pressurizing devices. This solves the technical problem in traditional electromagnetic crimping processes where micro-damage to the main cable insulation cannot be effectively repaired and is prone to developing into insulation degradation hazards.

[0023] 3) Significantly improved the uniformity of insulation repair agent distribution and repair effect. The extrusion pressure generated by the radial contraction of the crimping tube and the capillary action of the axial flow channel on the inner wall form a synergistic guiding mechanism, enabling the insulation repair agent to flow directionally along both sides of the insulation break and uniformly fill the interface gap between the cable insulation layer and the crimping tube, as well as the micro-cracks on the surface of the insulation layer and the end face of the insulation break. This forms a continuous, dense, and defect-free insulation repair layer, effectively avoiding repair failure caused by local accumulation or uneven distribution of the repair agent.

[0024] 4) The method of the present invention completes crimping and insulation repair simultaneously without adding extra steps and energy consumption; while maintaining the inherent advantages of electromagnetic crimping such as rapid forming and dense and gapless, it significantly improves the insulation performance and long-term operational reliability of cable joints. Attached Figure Description

[0025] The invention will now be further described with reference to the accompanying drawings.

[0026] Figure 1 This is a structural diagram of the cable connector assembly according to an embodiment of the present invention.

[0027] Figure 2 This is a flowchart of the cable joint insulation self-repairing electromagnetic crimping method according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the structure of the finished cable crimped product according to an embodiment of the present invention.

[0029] Figure 4 This is a temperature field distribution cloud map of the interface region between the cable insulation layer retention section and the crimping pipe obtained from the finite element simulation in Example 1.

[0030] Figure 5 This is a stress distribution cloud map of the interface region between the cable insulation layer retention section and the crimping tube obtained from the finite element simulation in Example 1.

[0031] The reference numerals in the attached diagram are as follows: 1. Cable, 101. Insulation break, 2. Crimping tube, 3. Self-healing layer, 4. Electromagnetic coil, 5. Diversion groove. Detailed Implementation

[0032] Example 1 This embodiment addresses the self-repair requirement of electromagnetic crimping insulation for 10kV XLPE power cables paired with GT-400 specification copper crimp connectors. It employs thermally responsive microcapsule technology to achieve in-situ synchronous repair of micro-damage to the cable insulation during the crimping process. The cable connector assembly structure of this embodiment is shown in Figure 1, the crimping process flow is shown in Figure 2, and the finished product after crimping is shown in Figure 2. Figure 3 As shown.

[0033] The self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules in this embodiment specifically includes the following steps: Step 1: Cable end pretreatment. Use a specialized cable stripping tool to perform standardized stripping on the ends of the two sections of cable to be connected, exposing 70mm of copper core. Use fine sandpaper to polish the surface of the cable insulation layer to remove burrs, and wipe it clean with anhydrous ethanol to ensure that the surface is free of oil and oxide layer.

[0034] Step 2: Machining a flow guide groove structure on the inner wall of the crimping tube. Using laser processing, axially distributed micro-flow guide grooves are machined on the inner surface of the crimping tube. The groove depth is 0.3mm, the groove width is 0.8mm, and the spacing between adjacent flow guide grooves is 3mm, ensuring that the flow guide grooves cover more than 50mm on both sides of the cable insulation break area.

[0035] Step 3: Multiphysics Coupling Modeling and Parameter Optimization. A multiphysics coupling finite element model of the electromagnetic crimping process (electromagnetic-thermal-mechanical) and a model of the thermal response microcapsule rupture behavior are established to simulate the thermal-mechanical coupling rupture behavior of the thermal response microcapsules during electromagnetic crimping. Based on the crimping specifications and insulation performance requirements of the cable joint, the parameters of the self-healing layer, the melting temperature window and particle size of the thermal response microcapsule shell, and the discharge voltage and discharge energy of the capacitive pulse power supply are determined.

[0036] The specific modeling and solution process is as follows: (1) Electromagnetic-thermal-mechanical multiphysics coupling control equations: Electromagnetic field governing equations: ; In the formula, γ For electrical conductivity, μ Permeability, J s This represents the source current density of the coil. It is determined by the vector magnetomotive force. A Eddy current density can be obtained and Joule heat source .

[0037] Transient heat conduction equation: ; In the formula, ρ For material density, C p The specific heat capacity at constant pressure of the material. k Let be the thermal conductivity of the material. The temperature distribution at the interface of the self-healing layer is obtained by solving for this value. T (x,t).

[0038] Structural dynamics equations: ; In the formula, uFor displacement, σ For stress tensor, For Lorentz force volume load, denoted as magnetic flux density.

[0039] Total strain includes elastic strain and thermal expansion strain: ; In the formula, For elastic strain, α The coefficient of thermal expansion; T ref This is a reference temperature (room temperature 25℃). I It is a second-order unit tensor.

[0040] From displacement field u The total strain field is calculated using geometric equations. ε Then, the stress tensor is calculated using the thermoelastic constitutive relation. σ : ; In the formula, C Let be the fourth elastic tensor of the material.

[0041] Calculation of the equivalent stress field using the Von Mises yield criterion: ; In the formula, , , for σ The three principal stresses. σ eq This refers to the interface equivalent force field that takes into account thermo-mechanical coupling.

[0042] (2) Thermal response microcapsule rupture behavior model To quantitatively describe the rupture behavior of the microcapsule shell under thermo-mechanical coupling, the rupture state variable D(t) is defined: ; In the formula, T s This is the softening temperature of the outer shell. T m The complete melting temperature ( T s < T m ), σ y The yield strength of the microcapsule shell material. t ruptureThe rupture characteristic time is the time required for D(t) to accumulate from 0 to 1 when the integrand is always 1. Its value is determined by the material properties and wall thickness of the microcapsule shell. When D(t) = 1, the microcapsule shell is considered to have completely ruptured, and the internal repair agent begins to be released. This model comprehensively reflects the synergistic effect of temperature and stress, consistent with the characteristic that microcapsule rupture is driven by both heat and force.

[0043] (3) Parametric simulation and optimization The above model was implemented in COMSOL Multiphysics simulation software, and parametric scans were performed on different operating conditions within the range of discharge voltage (15kV~25kV) and discharge energy (100kJ~200kJ). Simulation results show that when the discharge voltage is 20kV and the discharge energy is 150kJ, the peak temperature of the self-healing layer interface is 150℃, and the peak equivalent stress is 180MPa. Polyurea-formaldehyde resin microcapsules with a particle size of 100μm and a shell melting temperature window of 90℃~110℃ begin to soften approximately 8ms after the start of compression bonding and completely rupture at 16ms, with a rupture duration of approximately 8ms. The rupture range covers 60mm on both sides of the insulation break area, meeting the requirements for controllable rupture. The simulation also verified that the microcapsules remain intact under long-term constant temperature of 90℃ at a melting temperature of 90℃.

[0044] Step 4: Preparation of Thermally Responsive Microcapsules and Coating of Self-Healing Layer. Thermally responsive microcapsules were prepared using in-situ polymerization. The microcapsule shell material was polyurea-formaldehyde resin, with a particle size controlled at 100 μm. Two types of microcapsules were used: one type internally encapsulated with bisphenol A type epoxy resin E-51, and the other internally encapsulated with a modified fatty amine curing agent. The mass ratio of the two types of microcapsules was 1:1. The two types of thermally responsive microcapsules were uniformly premixed into a methyl silicone oil carrier. After thorough mixing, the mixture was evenly brushed onto the inner wall of the crimping tube and the outer surface of the cable's main insulation layer, with a coating thickness controlled at 200 μm, forming a self-healing layer.

[0045] Step 5: Cable joint pre-assembly. Align the two pre-treated cable ends, ensuring the core end faces fit tightly and are located at the axial midpoint of the crimping tube; coaxially sleeve the self-healing crimping tube onto the outside of the cable joint, aligning both ends of the crimping tube with the ends of the cable's main insulation layer, ensuring the guide groove completely covers the insulation break area and an area of ​​at least 50mm on each side.

[0046] Step 6: Electromagnetic crimping and controlled microcapsule rupture. The electromagnetic coil is coaxially sleeved in the preset crimping area outside the crimping tube. The electromagnetic coil is electrically connected to a capacitive pulse power supply via a vacuum discharge switch. The discharge voltage of the capacitive pulse power supply is set to 20kV, and the discharge energy to 150kJ. The energy storage capacitor is charged with a constant current. When the charging voltage reaches the set value, the vacuum discharge switch is triggered, applying a single-pulse high current to the electromagnetic coil.

[0047] Under the influence of a strong pulsed electromagnetic field, high-density eddy currents are induced within the crimping tube, generating a powerful radial Lorentz force that drives the crimping tube to undergo high-speed radial contraction deformation. Simultaneously, the local instantaneous temperature at the contact interface between the crimping tube and the self-healing layer reaches 150°C. The outer shell of the thermally responsive microcapsule undergoes controlled rupture under thermo-mechanical coupling, allowing the internal epoxy resin and curing agent components to flow out and mix. Under the combined effect of the radial contraction pressure of the crimping tube and the capillary action of the guide groove, the mixture flows axially and uniformly fills the interfacial gap between the cable insulation layer and the crimping tube, as well as the microcracks on the surface of the insulation layer and the end face of the insulation break. A very small amount of repair agent may overflow to the root of the exposed conductor section, but this does not affect the electrical connection performance between the conductor and the crimping tube.

[0048] In this embodiment, the temperature field distribution of the interface region between the cable insulation layer retention section and the crimping tube obtained by finite element simulation is shown in Figure 4, and the stress field distribution is shown in Figure 5. Figure 5 As shown.

[0049] Step 7: Curing of the insulation repair agent. After crimping, place the cable joint in a room temperature environment to cool naturally for 20 minutes. The mixed insulation repair agent will then complete the room temperature curing reaction, forming a dense insulation repair layer.

[0050] Based on testing and electric field simulation evaluation, the dielectric strength of the cured insulation repair layer is 35kV / mm.

[0051] Step 8: Finished Product Inspection. Remove the electromagnetic coil and perform a visual inspection and insulation performance test on the finished cable crimped product. (1) Visual inspection: The outer surface of the joint is smooth without cracks or obvious dents, and the crimped pipe has no axial movement; (2) Contact resistance test: The contact resistance of the connector conductor was measured using a DC resistance tester. The measured value was 8.2μΩ, which meets the requirement of ≤10μΩ; (3) Insulation resistance test: The insulation resistance of the joint was measured using a megohmmeter, and the measured value was 2.5 × 10⁻⁶. 9 Ω; (4) Partial discharge test: The partial discharge test was carried out in accordance with GB / T 3048.12-2007. The partial discharge initiation voltage was measured to be 42kV, and the partial discharge amount was less than 5pC at 1.73 times the rated voltage.

[0052] All test items passed, and the electromagnetic crimping operation of the cable joint in this embodiment is complete.

[0053] The apparatus for the above-mentioned cable joint insulation self-healing electromagnetic crimping method includes a cable 1, a crimping tube 2, a self-healing layer 3, an electromagnetic coil 4, and a capacitive pulse power supply. The cable 1 includes a conductor and an insulation layer covering the conductor; the self-healing layer 3 is disposed between the insulation layer of the cable 1 and the crimping tube 2, and contains thermally responsive microcapsules optimized by fracture behavior simulation; the inner wall of the crimping tube 2 has a pre-set flow channel structure; after the crimping tube 2 radially shrinks during electromagnetic crimping, it forms a tight bond with the insulation layer of the cable 1 through the cured insulation repair layer; the thermally responsive microcapsules in the self-healing layer 3 rupture after being triggered by the heat and force generated by electromagnetic crimping, releasing an insulation repair agent, which flows along the flow channel structure to fill the insulation break area and solidifies to form an insulation repair layer; during the electromagnetic crimping process, a pulsed electromagnetic field is applied through the electromagnetic coil 4, such as... Figure 1 As shown.

[0054] Example 2 The difference between the electromagnetic pressing method in this embodiment and the electromagnetic pressing method in Embodiment 1 is that the microcapsule shell is made of polymethyl methacrylate, the depth of the flow channel is 0.2 mm, the width of the channel is 0.5 mm, and the spacing between the flow channels is 2 mm.

[0055] The steps in this embodiment are the same as those in Embodiment 1.

[0056] Example 3 The difference between the electromagnetic crimping method in this embodiment and the electromagnetic crimping method in Embodiment 1 is that the self-healing layer is applied directly to the outer surface of the cable insulation layer and the inner wall of the crimping tube in powder form, with a coating thickness of 150μm, a discharge voltage of 18kV, and a discharge energy of 120kJ.

[0057] The steps in this embodiment are the same as those in Embodiment 1.

[0058] Implementation results demonstrate that this invention, through the construction of an electro-magnetic-thermal-mechanical multiphysics coupled finite element model and a microcapsule rupture behavior simulation model, achieves accurate prediction and optimized design of the microcapsule rupture process, ultimately realizing controllable microcapsule rupture. Simulation results show that under a 200kA pulsed current, a high-temperature zone with a peak temperature approaching or reaching 180℃ is formed at the interface between the coil and the press-fitting tube. Heat is rapidly conducted to the self-healing layer through the press-fitting tube, causing the temperature in the area of ​​the self-healing layer to reach and exceed the melting temperature window of the microcapsule shell, completely covering the location of the self-healing layer. This provides sufficient thermodynamic conditions for the precise triggering and controllable rupture of the microcapsule. Simultaneously, a high-stress zone is generated within the self-healing layer, with the Von Mises stress exceeding the yield strength of the microcapsule shell material, verifying that the microcapsule undergoes controllable rupture under the press-fitting thermo-mechanical coupling effect. Building upon this foundation, by pre-positioning thermally responsive microcapsules optimized through simulation, and combining them with the flow-guiding groove structure on the inner wall of the crimping connector, the inherent Joule heat and electromagnetic force of the electromagnetic crimping process were used as triggering conditions to achieve controllable rupture of the microcapsules to release the repair agent. The flow-guiding groove then guided the repair agent to uniformly fill the microcracks and interface gaps on the surface of the insulation layer. After crimping, the repair agent cured at room temperature to form an insulating repair layer. The crimped interface formed a dense, gapless insulating reinforcement layer, effectively increasing the partial discharge initiation voltage, extending the expected lifespan of the joint, and solving the technical challenge of easily and irreparably damaging the main insulation of the cable during electromagnetic crimping.

Claims

1. A self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules, characterized in that, A self-healing layer is provided on the inner wall of both ends of the crimping tube used for cable joint crimping. The self-healing layer is filled with thermally responsive microcapsules. During the cable joint crimping process, under the action of a pulsed electromagnetic field, the temperature of the end of the crimping tube rises and squeezes the self-healing layer, causing the thermally responsive microcapsules to rupture and release the insulating repair agent. The insulating repair agent flows along the guide groove on the inner wall of the crimping tube under the extrusion state, filling the interface gap between the cable insulation layer and the crimping tube, as well as the cracks on the surface of the insulation layer and the end face of the insulation break. After cooling, an insulating repair layer is formed between the cable insulation layer and the crimping tube. The method includes the following steps: Step 1: Pre-treat the ends of the cable to be crimped; Step 2: Use laser etching to process axially distributed guide grooves on the inner wall of the crimping tube; Step 3: Determine the parameters of the self-healing layer and the thermally responsive microcapsules according to the specifications of the cable joint crimping. Step 4: Based on the parameters obtained in Step 3, prepare thermally responsive microcapsules; coat the microcapsules in powder form or premixed into a silicone grease carrier evenly on the inner wall of the press-fit tube to form a self-healing layer; Step 5: Place the ends of the two cable connectors to be crimped together, and then put the crimping tube over the outside of the cable connector connection. Step 6: Place the electromagnetic coil outside the pressure tube and connect it to the pulse power supply via a switch. Set the discharge voltage and discharge energy of the pulse power supply. The control switch energizes the electromagnetic coil, and the crimping tube contracts radially and presses the cable under the action of the electromagnetic field. This triggers the controlled rupture of the thermal response microcapsule, releasing the insulation repair agent. Under the action of compression and the guiding action of the flow channel, the repair agent extends and covers the cable insulation break, filling the interface gap between the cable insulation layer and the crimping tube, as well as the cracks on the surface of the insulation layer and the end face of the insulation break. Step 7: Cool the crimped pipe to allow the insulating repair agent to cure and form an insulating repair layer; Step 8: Remove the electromagnetic coil, and conduct a visual inspection and insulation performance test on the finished cable crimped product. If it passes the test, the electromagnetic crimping of the cable joint is complete.

2. The cable joint insulation self-repairing electromagnetic crimping method according to claim 1, characterized in that, In step 3, a multi-physics coupled finite element model of electro-magnetism-thermal-mechanical fields and a thermal response microcapsule rupture behavior model are established. The above models are used to simulate the thermal-mechanical coupled rupture behavior of thermal response microcapsules in the electromagnetic crimping process. Based on the crimping forming specifications and insulation performance requirements of the cable joint, the parameters of the self-healing layer, the outer shell melting temperature window and particle size of the thermal response microcapsules, and the discharge voltage and discharge energy of the capacitive pulse power supply are determined.

3. The cable joint insulation self-repairing electromagnetic crimping method according to claim 1, characterized in that, In step 2, the guide grooves on the inner wall of the pressure pipe are axially distributed, with a groove depth of 0.2mm to 0.5mm and a groove width of 0.5mm to 1mm.

4. The cable joint insulation self-repairing electromagnetic crimping method according to claim 2, characterized in that, In step 3, the melting temperature of the thermally responsive microcapsule shell is 90°C to 110°C, and the shell material is polyurea-formaldehyde resin or polymethyl methacrylate.

5. The cable joint insulation self-repairing electromagnetic crimping method according to claim 2, characterized in that, In step 3, the particle size of the thermally responsive microcapsules is 50 μm to 200 μm; The thermally responsive microcapsules are of two types: one type encapsulates an epoxy resin component, and the other type encapsulates a curing agent component. The two types of thermally responsive microcapsules are uniformly mixed and distributed in the self-healing layer.

6. The cable joint insulation self-repairing electromagnetic crimping method according to claim 2, characterized in that, In step 4, the thermally responsive microcapsules are applied directly in powder form or premixed into the silicone grease carrier and then uniformly coated on the outer surface of the insulating layer and the inner wall of the compression fitting to form a self-healing layer.

7. The cable joint insulation self-healing electromagnetic crimping method according to claim 2, characterized in that, In step 5, the discharge voltage of the capacitor pulse power supply is 15kV to 25kV, and the discharge energy is 100kJ to 200kJ.

8. The cable joint insulation self-repairing electromagnetic crimping method according to claim 2, characterized in that, In step 6, the local instantaneous temperature at the contact interface between the pressure tube and the self-modifying layer is 120°C to 180°C, ensuring that the outer shell of the thermally responsive microcapsule completely softens and ruptures, and that the repair agent flows effectively, thus achieving controllable rupture of the microcapsule.

9. The cable joint insulation self-repairing electromagnetic crimping method according to claim 2, characterized in that, In step 7, the dielectric strength of the cured insulating repair layer is not less than 30 kV / mm, and the volume resistivity is not less than 10 kV / mm. 15 Ω·cm.

10. An apparatus for implementing the self-healing electromagnetic crimping method for cable joint insulation using thermally responsive microcapsules as described in any one of claims 1-9, characterized in that, Includes press-fit tubing, self-healing layer, electromagnetic coil, and capacitive pulse power supply; The inner wall of the press-fit tube is provided with an axially distributed flow guide groove structure; the press-fit tube is configured to radially contract under the action of the pulsed electromagnetic field generated by the energization of the electromagnetic coil; The self-healing layer is disposed between the cable insulation layer and the crimping tube, and the self-healing layer contains thermally responsive microcapsules; The thermally responsive microcapsules are configured to rupture controllably and release an insulating repair agent under the thermal and mechanical coupling effect generated by electromagnetic crimping. The insulating repair agent can flow along the flow channel structure, fill the interface gap between the cable insulation layer and the crimping tube, as well as the cracks on the surface of the insulation layer and the end face of the insulation break. After cooling and solidification, an insulating repair layer is formed, so that the crimping tube and the cable insulation layer form a tight bond through the insulating repair layer. The electromagnetic coil is sleeved on the outside of the pressure tube and connected to the capacitive pulse power supply via a discharge switch.

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