A 27.5kv electrified railway power cable with self-repairing capability and a preparation method thereof

Abstract

The application discloses a 27.5kV electrified railway power cable with self-repairing capability and a preparation method, and belongs to the technical field of power cable manufacturing. The cable comprises, from inside to outside, a copper conductor, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a buffer water-blocking layer, a non-magnetic armored layer, an outer sheath, and a self-repairing triggering unit arranged between the armored layer and the outer sheath. The self-repairing triggering unit comprises a fixing support, a piercing needle body and a sealed storage cavity. The piercing needle body faces the inner wall of the outer sheath and keeps a preset gap with the inner wall. The sealed storage cavity is filled with a moisture-curing repair agent. When the outer sheath is damaged, the inner wall of the damaged outer sheath contacts and pushes the piercing needle body to pierce the sealed storage cavity and release the repair agent. The repair agent is cured and blocked after contacting moisture, thereby solving the problems that the existing railway cable cannot be self-repaired after the outer sheath is damaged, and the repair scheme is not suitable for medium and high voltage railway working conditions. The application does not change the electric field distribution, does not require external energy, and can reduce operation and maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of power cable manufacturing technology, specifically relating to a 27.5kV electrified railway power cable with self-healing capability and its preparation method. Background Technology

[0002] As the core carrier of the rail transit network, the stability of the traction power supply system of electrified railways directly determines the safety of railway operation. 27.5kV single-phase AC power cables, as a key component of the traction power supply system of electrified railways, are mainly used for power transmission from traction substations to the overhead contact line. Their operational reliability directly determines railway traffic safety and operational efficiency. With the development of railways towards high speed, high density, and heavy loads, the cable laying environment is becoming increasingly complex, facing multiple harsh operating conditions for extended periods. Defects and faults are becoming increasingly prominent, becoming a key bottleneck restricting the stability of the traction power supply system. Currently, although 27.5kV railway cables generally meet conventional power supply requirements, significant defects still exist. Long-term laying in complex environments such as railway tunnels, bridges, direct burial, and outdoor areas makes them highly susceptible to mechanical compression, bending fatigue, environmental erosion, and external damage, leading to cracked outer sheaths and damaged insulation layers due to moisture. This can cause faults such as electric field imbalance, partial discharge, and insulation breakdown, seriously affecting the continuity of railway power supply. Meanwhile, railway cables are mostly laid in a concealed manner, making it difficult to detect early minor damage during routine inspections. After a fault occurs, the repair process is complex and time-consuming, which seriously affects the normal operation of the railway and keeps maintenance costs high.

[0003] Existing technologies primarily enhance protective performance through methods such as thickening the sheath, optimizing armor, and strengthening shielding. However, these methods only provide passive protection and cannot autonomously repair existing micro-damage. Although self-healing materials are gradually being applied in the power equipment field, most solutions suffer from low triggering accuracy, poor compatibility with cable substrates, and impact on electrical insulation performance. Furthermore, they are difficult to adapt to the 27.5kV medium-high voltage traction power supply environment. 27.5kV electrified railway power cables are prone to damage, difficult to self-heal, challenging to maintain, and costly, making them unsuitable for the high-quality development needs of my country's railways. Developing a 27.5kV self-healing power cable that can be passively triggered and autonomously repaired without affecting electrical performance and adaptable to complex operating conditions is of significant practical importance for improving the reliability of traction power supply systems, reducing maintenance costs, and ensuring the safe and efficient operation of railways. Patent application CN119724762A discloses a self-healing smart cable and its preparation and system scheme. The cable, from the inside out, consists of a copper conductor, an XLPE base insulation layer, a smart control layer containing photo-water-mechanical triple-response microcapsules, an outer repair layer based on dynamic covalent bonds, and a low-smoke halogen-free outer protective layer with distributed optical fiber sensors. It is prepared using conductor pretreatment, three-layer co-extrusion insulation, low-temperature extrusion of the smart control layer, UV curing of the repair layer, and simultaneous embedding of optical fibers. It is equipped with a closed-loop smart repair system that monitors temperature, strain, partial discharge, and other states in real time through optical fibers and electric field sensors. Depending on the degree of damage, it initiates microcapsule repair and dynamic bond self-repair through autonomous closure, light triggering, or heat triggering, achieving automatic detection and efficient repair of cable damage, improving cable reliability and service life. However, the material and processing costs are much higher than ordinary 27.5kV railway cables, hindering large-scale promotion. Triggering and repair have limitations: light and heat triggering require external auxiliary devices, which are difficult to implement in tunnels, outdoor environments, or other scenarios without external power sources; and in cases of deep insulation damage, the repair agent has difficulty reaching the defect location. Dynamic bond materials and microcapsules are prone to aging and failure under long-term vibration and high / low temperature cycling conditions in railways. The provided external sensing and control system poses compatibility risks with the railway power supply system, potentially causing electromagnetic interference, and device failure increases the complexity of cable maintenance. Chinese patent application CN116228415A discloses a microcapsule-type intelligent repair method for high-voltage cable buffer layers. This method incorporates temperature-responsive microcapsules containing a repair agent encapsulated within the cable buffer layer. When the cable buffer layer suffers damage such as temperature rise or ablation due to poor contact, the heat triggers the microcapsules to rupture and release liquid repair agent. The repair agent can impregnate and fill the damaged gaps in the buffer layer and quickly solidify, thereby restoring the electrical contact and mechanical adhesion between the buffer layer and the metal sheath, achieving in-situ automatic repair of buffer layer damage, and improving the stability and service life of the cable. However, the adopted technical solution has the following drawbacks: it only addresses ablation damage to the buffer layer and cannot repair damage to the outer sheath, insulation layer, or other parts.Microcapsules lack stability and are prone to premature rupture under vibration and compression during long-term operation, leading to the failure of the repair agent and loss of its repair capabilities. After the repair agent solidifies, it may cause uneven electric field distribution, easily triggering partial discharge and affecting the insulation safety of high-voltage cables.

[0004] There is an urgent need to find a 27.5kV electrified railway power cable with self-healing capabilities, so that the cable can repair itself when damaged by the external environment, and ensure that the self-healing material is combined with the cable to avoid electromagnetic interference, ensure reliable operation of the cable, and extend the service life of the cable. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a 27.5kV electrified railway power cable with self-healing capability and a method for its preparation, so as to solve the technical problems that the outer sheath of existing 27.5kV railway cables cannot be repaired on their own after damage and that existing repair technologies are not applicable to medium and high voltage railway operating conditions.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a 27.5kV electrified railway power cable with self-healing capability, which includes, from the inside out, a copper conductor, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a buffer water-blocking layer, a non-magnetic armor layer, an outer sheath, and a self-healing triggering unit disposed between the non-magnetic armor layer and the outer sheath. The self-healing trigger unit includes a fixed bracket, a puncture needle, and a sealed storage cavity; the fixed bracket is fixed to the outer surface of the non-magnetic armor layer, the puncture needle is set on the fixed bracket and faces the inner wall of the outer sheath, and the sealed storage cavity is attached to the outer surface of the non-magnetic armor layer and is filled with repair agent; there is a preset gap between the tip of the puncture needle and the inner wall of the outer sheath. When the outer sheath is damaged, the inner wall of the outer sheath at the damaged point deforms towards the non-magnetic armor layer, thereby contacting and pushing the tip of the piercing needle, causing the piercing needle to pierce the sealed storage cavity and release the repair agent. The repair agent solidifies after contact with external moisture to seal the damage.

[0007] Preferably, the self-healing trigger units are arranged at equal intervals along the cable axis, with an axial interval of 1.5 meters, and two units are evenly distributed in the circumferential direction.

[0008] Preferably, the preset gap between the puncture needle and the inner wall of the outer sheath is 0.2 to 0.5 mm; the repair agent filled in the sealed storage cavity is a moisture-curing polyurethane foam colloid material.

[0009] Preferably, the non-magnetic armor layer is made of non-magnetic aluminum wire armor, with an armor pitch of 8 to 12 times the outer diameter of the cable; the buffer water-blocking layer is made of semi-conductive buffer water-blocking tape wrapped in an overlapping manner, with an overlap rate of 20% to 30%; and the outer sheath is made of low-smoke halogen-free flame-retardant polyolefin material.

[0010] Preferably, the copper conductor is a multi-strand oxygen-free copper wire tightly stranded structure, the stranding direction is right-handed, and the compaction coefficient is not less than 0.9; the conductor shielding layer and the insulating shielding layer are both semi-conductive cross-linked polyethylene materials, the XLPE insulating layer is a cross-linked polyethylene material for 27.5kV medium voltage cables, and the conductor shielding layer, XLPE insulating layer and insulating shielding layer are three-layer co-extruded integral structures.

[0011] This invention also discloses a method for preparing the aforementioned self-healing 27.5kV electrified railway power cable, comprising the following steps: Step 1: Prepare copper conductor by tightly stranding multiple strands of oxygen-free copper wire. After stranding, straighten, polish and ultrasonically clean the surface of the copper conductor. Step 2: A conductor shielding layer, an XLPE insulation layer, and an insulation shielding layer are sequentially coated onto the copper conductor using a three-layer co-extrusion process, followed by cross-linking reaction and cooling for shaping; Step 3: Wrap a buffer water-blocking layer over the insulating shielding layer; Step 4: Apply armor to the outside of the buffer water-resistant layer to form a non-magnetic armor layer; Step 5: Install the self-healing trigger unit at intervals along the cable axis on the outer surface of the non-magnetic armor layer, with the piercing needle facing outwards, and the sealed storage cavity attached to the outer wall of the non-magnetic armor layer. The sealed storage cavity is filled with a moisture-curing repair agent. Step 6: Extrude an outer sheath over the non-magnetic armor layer containing the self-healing trigger unit to maintain a preset gap between the piercing needle and the inner wall of the outer sheath.

[0012] Preferably, in step one, the copper conductor is stranded in a right-hand direction, and the compression factor is not less than 0.9; In step two, the copper conductor is preheated at 80-100℃, the temperature of each section of the extruder is 110-140℃, the crosslinking tube temperature is 180-200℃, the crosslinking pressure is 0.6-0.8MPa, and the degree of crosslinking of the XLPE insulation layer after crosslinking is not less than 92%.

[0013] Preferably, in step three, the buffer water-blocking layer is made of semi-conductive buffer water-blocking tape wrapped in an overlapping manner, with an overlap rate of 20% to 30%.

[0014] Preferably, in step four, the armor is made of non-magnetic aluminum wire, and the armor pitch of the non-magnetic armor layer is 8 to 12 times the outer diameter of the cable.

[0015] Preferably, in step five, the self-healing trigger units are installed at 1.5-meter intervals along the cable axis, with two units evenly distributed in the circumferential direction; In step six, the outer sheath is extruded with low-smoke halogen-free flame-retardant polyolefin material at an extrusion temperature of 160-190℃. The preset gap between the puncture needle and the inner wall of the outer sheath is 0.2-0.5mm. The repair agent filled in the sealed storage cavity is moisture-curing polyurethane foam material.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a 27.5kV electrified railway power cable with self-healing capability. By using a self-healing trigger unit positioned between the non-magnetic armor layer and the outer sheath, it solves the technical problems of existing 27.5kV railway cables, which are prone to cracking and damage due to mechanical compression and external forces in complex laying environments such as tunnels, bridges, direct burial, and outdoor locations. Furthermore, these cables are unable to self-repair after damage, are difficult to detect during inspections, and require complex and time-consuming fault repair, severely impacting normal railway operation. The self-healing trigger unit includes a fixed bracket fixed to the outer surface of the non-magnetic armor layer, a piercing needle mounted on the fixed bracket and facing the inner wall of the outer sheath, and a sealed storage cavity fitted to the outer surface of the non-magnetic armor layer and filled with a moisture-curing repair agent. A preset gap exists between the tip of the piercing needle and the inner wall of the outer sheath. This structure achieves passive, in-situ self-healing without relying on external power sources or complex intelligent monitoring equipment. When the outer sheath is damaged by external force, the inner wall of the outer sheath at the damaged point deforms towards the non-magnetic armor layer, thereby contacting and pushing the tip of the piercing needle. This causes the piercing needle to pierce the sealed storage cavity and release the repair agent. The repair agent solidifies upon contact with external moisture to seal the damage. Under normal cable operation, the piercing needle maintains a preset gap with the inner wall of the outer sheath, without changing the original electric field distribution of the cable or interfering with the insulation strength of the 27.5kV high-voltage system. This effectively eliminates electric field concentration points and meets the electrical safety standards for railway high-voltage cables. When the outer sheath is damaged, the leak can be actively sealed without manual intervention, effectively preventing insulation breakdown, partial discharge, and other faults caused by damage propagation. This significantly reduces the risk of sudden power outages and ensures the continuous and stable operation of the electrified railway traction power supply system. Furthermore, it does not require an external power supply or complex intelligent monitoring equipment. It achieves in-situ self-repair through a passive triggering structure. The repair materials are inexpensive and the process is simple, which can significantly reduce the frequency of manual inspections and emergency repairs, and significantly reduce the maintenance investment throughout the cable's life cycle.

[0017] The method for preparing the above-mentioned 27.5kV electrified railway power cable with self-healing capability disclosed in this invention solves the technical problems of how to coordinate the preparation of the self-healing structure with the multi-layer structure of the high-voltage cable and how to integrate the self-healing function into the internal structure of the cable while ensuring the original electrical performance and mechanical strength of the cable. The conductor surface is ensured to be round and smooth by straightening, grinding and ultrasonic cleaning after stranding, providing a stable coating foundation for subsequent three-layer co-extrusion. The three-layer co-extrusion process is used to sequentially coat the copper conductor with a conductor shielding layer, an XLPE insulation layer and an insulation shielding layer, followed by cross-linking reaction and cooling to shape, so that the insulation system meets the requirements of 27.5kV medium and high voltage power supply. Radial water blocking and extrusion mechanical protection are provided by wrapping with a buffer water-blocking layer and non-magnetic armor. The self-healing trigger unit is installed at intervals along the cable axis on the outer surface of the armor layer, with the piercing needle facing outward and the sealed storage cavity attached to the outer wall of the armor layer. The overall extrusion coating of the outer sheath maintains a preset gap between the piercing needle and the inner wall of the outer sheath. This process sequence ensures the precise positioning of the trigger unit in the cable structure, so that the repair function works synergistically with the various layers of the cable structure. Conductor preheating temperature of 80-100℃ and extruder section temperature of 110-140℃ ensure uniform plasticization of each layer of material; cross-linking tube temperature of 180-200℃ and cross-linking pressure of 0.6-0.8MPa ensure that the cross-linking degree of XLPE insulation layer is not less than 92%, and that there are no bubbles, impurities, or eccentric defects, meeting the requirements of 27.5kV power frequency withstand voltage and partial discharge index; the non-magnetic aluminum wire armor pitch is controlled at 8-12 times the cable outer diameter, which can effectively avoid eddy currents generated by single-phase power supply in electrified railways. The design minimizes cable loss while maintaining both mechanical strength and electrical safety. Self-repairing trigger units are arranged in groups of 1.5 meters along the cable axis and two units are evenly distributed circumferentially, enabling damage detection coverage across the entire cable length. An outer sheath extrusion temperature of 160–190℃ ensures a preset gap of 0.2–0.5 mm between the puncture needle and the inner wall of the outer sheath after molding. The repair materials are inexpensive and the process is simple, significantly reducing the frequency of manual inspections and emergency repairs, and substantially lowering maintenance costs throughout the cable's lifecycle. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the 27.5kV electrified railway power cable with self-healing capability of the present invention.

[0019] The components are: 1. Copper conductor; 2. Conductor shielding layer; 3. XLPE insulation layer; 4. Insulation shielding layer; 5. Buffer water-blocking layer; 6. Non-magnetic armor layer; 7. Outer sheath; 8. Self-healing trigger unit; 81. Fixing bracket; 82. Puncture needle body; 83. Sealed storage cavity. Detailed Implementation

[0020] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] This invention proposes a 27.5kV electrified railway power cable with self-healing capability. In order to enable the cable to repair itself when damaged by external environment, the self-healing material is combined with the cable to avoid electromagnetic interference, ensure reliable operation of the cable, and extend the service life of the cable.

[0027] The 27.5kV electrified railway power cable with self-healing capability disclosed in this invention consists of the following components from the inside out: copper conductor 1, conductor shielding layer 2, XLPE insulation layer 3, insulation shielding layer 4, buffer water-blocking layer 5, non-magnetic armor layer 6, and outer sheath 7. Self-healing trigger units 8 are arranged at equal intervals along the cable axis inside the outer sheath 7 and between the buffer water-blocking layer 5.

[0028] This invention provides a 27.5kV electrified railway power cable with self-healing capability. The cable, from the outside to the inside, comprises, from the inside to the outside: a copper conductor 1, a conductor shielding layer 2, an XLPE insulation layer 3, an insulation shielding layer 4, a buffer water-blocking layer 5, a non-magnetic armor layer 6, an outer sheath 7, and a self-healing trigger unit 8. The self-healing trigger unit 8 includes a fixed bracket 81, a puncture needle 82, and a sealed storage cavity 83. This unit is uniformly arranged along the cable axis between the armor layer 6 and the outer sheath 7. The copper conductor 1 is made of multiple strands of oxygen-free copper wire tightly stranded in a right-hand direction with a compaction coefficient of not less than 0.9. The conductor cross-section is selected according to the traction power supply current carrying capacity requirements. After stranding, the conductor surface is straightened, polished and ultrasonically cleaned to remove burrs, oil and oxide layers, ensuring that the conductor surface is round and smooth, providing a stable coating foundation for subsequent three-layer co-extrusion.

[0029] The conductor shielding layer 2, XLPE insulation layer 3, and insulation shielding layer 4 are co-extruded using a three-layer co-extrusion process. On the extrusion production line, conductor shielding layer 2, XLPE insulation layer 3, and insulation shielding layer 4 are sequentially coated. Conductor shielding layer 2 and insulation shielding layer 4 are made of semi-conductive cross-linked polyethylene material, while XLPE insulation layer 3 uses cross-linked polyethylene material specifically for 27.5kV medium-voltage cables. During extrusion, the conductor preheating temperature is controlled between 80℃ and 100℃, and the temperature of each section of the extruder is set between 110℃ and 140℃ to ensure uniform plasticization of each layer. After extrusion, the cable enters the cross-linking tube for cross-linking reaction. The cross-linking tube temperature is between 180℃ and 200℃, and the cross-linking pressure is between 0.6MPa and 0.8MPa. After cross-linking, the cable is cooled and shaped to ensure that the cross-linking degree of XLPE insulation layer 3 is not less than 92%, and that it is free of bubbles, impurities, and eccentric defects, meeting the requirements for 27.5kV power frequency withstand voltage and partial discharge indicators.

[0030] The buffer water-blocking layer 5 is wrapped around the outside of the insulating shielding layer 4 using a semi-conductive buffer water-blocking tape. The wrapping overlap rate is controlled at 20% to 30%, and the tension is uniform, forming a continuous and dense buffer water-blocking layer 5. This layer has the functions of radial water blocking and buffering mechanical stress, which can effectively prevent the subsequent armor layer from damaging the insulation system.

[0031] The non-magnetic armor layer 6 uses non-magnetic aluminum wire to armor the buffer water-blocking layer 5. The diameter of the armor aluminum wire is selected according to the mechanical performance requirements of the cable. The armor pitch is controlled at 8 to 12 times the outer diameter of the cable, and the tension is uniform to avoid eddy current loss. It is suitable for the single-phase traction power supply environment of electrified railways, and at the same time improves the cable's resistance to compression and shear.

[0032] The self-healing trigger unit 8 is installed on the fixed bracket 81, with one group every 1.5 meters along the cable axis, and two evenly distributed in the circumferential direction. It is fixed around the outer surface of the armor layer 6. During installation, the piercing needle 82 is ensured to face outward and directly onto the inner side of the outer sheath 7. The sealed storage cavity 83 is filled with moisture-curing polyurethane foam material and adheres to the outer wall of the armor layer 6. After all units are installed, the outer sheath 7, made of low-smoke halogen-free flame-retardant polyolefin material, is extruded and coated as a whole. The extrusion temperature is 160℃~190℃ and the extrusion pressure is stable to ensure that after the outer sheath 7 is formed, the piercing needle 82 and the inner wall of the outer sheath 7 maintain a preset gap of 0.2mm~0.5mm, which does not affect the electric field distribution during normal cable operation.

[0033] This invention achieves proactive prevention and self-repair, significantly improving power supply reliability. Through a pre-set self-repair trigger unit 8, when the outer sheath 7 is damaged, the leak can be proactively sealed without manual intervention, effectively preventing insulation breakdown, partial discharge, and other faults caused by the damage's spread. This greatly reduces the risk of sudden power outages and ensures the continuous and stable operation of the electrified railway traction power supply system.

[0034] This invention provides an electric field distribution that ensures high-voltage electrical safety. The self-healing trigger unit 8, through its positioning design with the fixed bracket 81 and the piercing needle 82, maintains a preset gap with the inner wall of the outer sheath 7 during normal cable operation, thus not altering the original electric field distribution of the cable and not interfering with the insulation strength of the 27.5kV high-voltage system. Simultaneously, each layer of the structure employs a standard shielding design, effectively eliminating electric field concentration points and meeting the electrical safety standards for railway high-voltage cables.

[0035] This invention is adaptable to complex operating conditions and reduces the overall lifecycle maintenance cost. It employs a non-magnetic aluminum wire armor structure, effectively avoiding eddy current losses caused by single-phase power supply in electrified railways, while balancing mechanical strength and electrical safety. The outer sheath 7 is made of low-smoke, halogen-free flame-retardant material, exhibiting strong anti-aging and corrosion resistance. This solution requires no external power supply or complex intelligent monitoring equipment, achieving in-situ self-repair through a passive triggering structure. The repair materials are inexpensive and the process is simple, significantly reducing the frequency of manual inspections and emergency repairs, thus substantially reducing the overall lifecycle maintenance investment of the cable. It has extremely high engineering promotion value and economic benefits.

[0036] The key technical point of this invention is the collaborative design of a passive puncture-type self-healing unit and a multi-layer cable structure, which is suitable for 27.5kV railway cable conditions; the protection points cover the overall cable structure, the self-healing trigger unit 8 components, the corresponding manufacturing process, and railway application scenarios.

[0037] See Figure 1 This is a schematic diagram of the structure of the 27.5kV electrified railway power cable with self-healing capability of the present invention. As can be seen from the figure, the cable has a seven-layer structure from the inside out, consisting of a copper conductor 1, a conductor shielding layer 2, an XLPE insulation layer 3, an insulation shielding layer 4, a buffer water-blocking layer 5, a non-magnetic armor layer 6, and an outer sheath 7. The copper conductor 1 is located at the very center and is made of multiple strands of oxygen-free copper wire tightly twisted together. The conductor shielding layer 2, the XLPE insulation layer 3, and the insulation shielding layer 4 form the main insulation system of the cable through a three-layer co-extrusion process. The buffer water-blocking layer 5 is wrapped around the insulation shielding layer 4 to provide radial water blocking and buffer protection. The non-magnetic aluminum wire armor layer 6 provides mechanical protection against compression and shearing and avoids eddy current loss. A self-healing trigger unit 8 is provided between the non-magnetic armor layer 6 and the outer sheath 7. The self-healing trigger unit 8 is fixed around the outer surface of the armor layer 6 by a fixing bracket 81. The fixing bracket 81 supports a piercing needle 82 facing outwards and towards the inner side of the outer sheath 7, as well as a sealed storage cavity 83 that fits against the outer wall of the armor layer 6. The sealed storage cavity 83 is filled with moisture-curing polyurethane foam. A preset gap of 0.2 to 0.5 mm is maintained between the tip of the piercing needle 82 and the inner wall of the outer sheath 7. This gap ensures that the self-healing trigger unit 8 does not contact the outer sheath 7 under normal cable operation, thus not changing the original electric field distribution of the cable and not interfering with the insulation strength of the 27.5kV high-voltage system. When the outer sheath 7 is damaged, the external force at the damaged point causes the inner wall of the outer sheath 7 to press inwards and push the piercing needle 82, causing it to pierce the sealed storage cavity 83 and release the repair agent. The repair agent foams and cures after contacting external moisture, sealing the damage. The self-repair trigger unit 8 is set at 1.5-meter intervals along the cable axis, with two units evenly distributed in the circumferential direction of the same cross section. This enables comprehensive perception and autonomous repair of damage to the outer sheath 7 along the entire length of the cable, without the need for an external power supply or complex monitoring equipment.

[0038] Example 1 A 27.5kV electrified railway power cable with self-healing capability, comprising: The copper conductor 1 is made of multiple strands of oxygen-free copper wire tightly stranded in a right-hand direction with a compaction coefficient of 0.92. After stranding, the surface of the copper conductor 1 is straightened, polished, and ultrasonically cleaned to remove burrs, oil, and oxide layers, ensuring a smooth and round surface. A three-layer co-extrusion process is used to sequentially coat the copper conductor 1 with a conductor shielding layer 2, an XLPE insulation layer 3, and an insulation shielding layer 4. The conductor shielding layer 2 and the insulation shielding layer 4 are made of semi-conductive cross-linked polyethylene material, while the XLPE insulation layer 3 is made of 27.5kV medium-voltage cable-specific cross-linked polyethylene material. During extrusion, the preheating temperature of the copper conductor 1 is 90℃, and the temperature of each section of the extruder is 125℃. After extrusion, the cable enters the cross-linking tube for cross-linking reaction. The cross-linking tube temperature is 190℃, and the cross-linking pressure is 0.7MPa. After cross-linking, the cable is cooled and shaped. The cross-linking degree of the XLPE insulation layer 3 is 94%, with no bubbles, impurities, or eccentric defects. A semi-conductive buffer water-blocking tape is overlapped and wrapped around the outside of the insulating shielding layer 4 to form a buffer water-blocking layer 5. The wrapping overlap rate is 25%, and the tension is uniform, forming a continuous and dense buffer water-blocking layer 5. Non-magnetic aluminum wire is used to armor the buffer water-blocking layer 5 to form a non-magnetic armor layer 6. The armor pitch is 10 times the outer diameter of the cable, and the tension is uniform. The self-healing trigger unit 8 is fixed around the outer surface of the non-magnetic armor layer 6 by the fixing bracket 81. Two units are evenly distributed in the circumferential direction at 1.5-meter intervals along the cable axis. During installation, the puncture needle 82 faces outward and is directly inside the outer sheath 7. The sealed storage cavity 83 is filled with moisture-curing polyurethane foam material and adhered to the outer wall of the non-magnetic armor layer 6. After all units are deployed, the outer sheath 7 is extruded and coated with low-smoke halogen-free flame-retardant polyolefin material. The extrusion temperature is 175℃, and the extrusion pressure is stable. After the outer sheath 7 is formed, the puncture needle 82 and the inner wall of the outer sheath 7 maintain a preset gap of 0.35mm.

[0039] Example 2 A 27.5kV electrified railway power cable with self-healing capability, comprising: The copper conductor 1 is made of multiple strands of oxygen-free copper wire tightly stranded in a right-hand direction with a compaction coefficient of 0.90. After stranding, the surface of the copper conductor 1 is straightened, polished, and ultrasonically cleaned to remove burrs, oil, and oxide layers, ensuring a smooth and round surface. A three-layer co-extrusion process is used to sequentially coat the copper conductor 1 with a conductor shielding layer 2, an XLPE insulation layer 3, and an insulation shielding layer 4. The conductor shielding layer 2 and the insulation shielding layer 4 are made of semi-conductive cross-linked polyethylene material, while the XLPE insulation layer 3 is made of 27.5kV medium-voltage cable-specific cross-linked polyethylene material. During extrusion, the copper conductor 1 is preheated to 80℃, and the temperature of each section of the extruder is 110℃. After extrusion, the cable enters the cross-linking tube for cross-linking reaction. The cross-linking tube temperature is 180℃, and the cross-linking pressure is 0.6MPa. After cross-linking, the cable is cooled and shaped. The cross-linking degree of the XLPE insulation layer 3 is 92%, free of bubbles, impurities, and eccentric defects. A semi-conductive buffer water-blocking tape is overlapped and wrapped around the outside of the insulating shielding layer 4 to form a buffer water-blocking layer 5. The wrapping overlap rate is 20%, and the tension is uniform, forming a continuous and dense buffer water-blocking layer 5. Non-magnetic aluminum wire is used to armor the buffer water-blocking layer 5 to form a non-magnetic armor layer 6. The armor pitch is 8 times the outer diameter of the cable, and the tension is uniform. The self-healing trigger unit 8 is fixed around the outer surface of the non-magnetic armor layer 6 by the fixing bracket 81. Two units are evenly distributed in the circumferential direction at 1.5-meter intervals along the cable axis. During installation, the puncture needle 82 faces outward and is directly inside the outer sheath 7. The sealed storage cavity 83 is filled with moisture-curing polyurethane foam material and adhered to the outer wall of the non-magnetic armor layer 6. After all units are deployed, the outer sheath 7 is extruded and coated with low-smoke halogen-free flame-retardant polyolefin material. The extrusion temperature is 160℃, and the extrusion pressure is stable. After the outer sheath 7 is formed, the puncture needle 82 and the inner wall of the outer sheath 7 maintain a preset gap of 0.20mm.

[0040] Example 3 A 27.5kV electrified railway power cable with self-healing capability, comprising: The copper conductor 1 is made of multiple strands of oxygen-free copper wire tightly stranded in a right-hand direction with a compaction coefficient of 0.95. After stranding, the surface of the copper conductor 1 is straightened, polished, and ultrasonically cleaned to remove burrs, oil, and oxide layers, ensuring a smooth and round surface. A three-layer co-extrusion process is used to sequentially coat the copper conductor 1 with a conductor shielding layer 2, an XLPE insulation layer 3, and an insulation shielding layer 4. The conductor shielding layer 2 and the insulation shielding layer 4 are made of semi-conductive cross-linked polyethylene material, while the XLPE insulation layer 3 is made of 27.5kV medium-voltage cable-specific cross-linked polyethylene material. During extrusion, the copper conductor 1 is preheated to 100℃, and the temperature of each section of the extruder is 140℃. After extrusion, the cable enters the cross-linking tube for cross-linking reaction. The cross-linking tube temperature is 200℃, and the cross-linking pressure is 0.8MPa. After cross-linking, the cable is cooled and shaped. The cross-linking degree of the XLPE insulation layer 3 is 95%, with no bubbles, impurities, or eccentric defects. A semi-conductive buffer water-blocking tape is overlapped and wrapped around the outside of the insulating shielding layer 4 to form a buffer water-blocking layer 5. The wrapping overlap rate is 30%, and the tension is uniform, forming a continuous and dense buffer water-blocking layer 5. Non-magnetic aluminum wire is used to armor the buffer water-blocking layer 5 to form a non-magnetic armor layer 6. The armor pitch is 12 times the outer diameter of the cable, and the tension is uniform. The self-healing trigger unit 8 is fixed around the outer surface of the non-magnetic armor layer 6 by the fixing bracket 81. Two units are evenly distributed in the circumferential direction at 1.5-meter intervals along the cable axis. During installation, the puncture needle 82 faces outward and is directly inside the outer sheath 7. The sealed storage cavity 83 is filled with moisture-curing polyurethane foam material and adhered to the outer wall of the non-magnetic armor layer 6. After all units are deployed, the outer sheath 7 is extruded and coated with low-smoke halogen-free flame-retardant polyolefin material. The extrusion temperature is 190℃, the extrusion pressure is stable, and after the outer sheath 7 is formed, the puncture needle 82 and the inner wall of the outer sheath 7 maintain a preset gap of 0.50mm.

[0041] In summary, the present invention discloses a 27.5kV electrified railway power cable with self-healing capability and its preparation method. Through the system integration design of the cable layered structure and the self-healing trigger unit, it solves the technical problems of 27.5kV electrified railway power cables being difficult to self-repair, difficult to detect during inspection, and complex and time-consuming fault repair in complex laying environments such as tunnels, bridges, direct burial, and field, which seriously affect the normal operation of railways. The cable consists of, from the inside out, a copper conductor 1, a conductor shielding layer 2, an XLPE insulation layer 3, an insulation shielding layer 4, a buffer water-blocking layer 5, a non-magnetic armor layer 6, and an outer sheath 7, forming a complete high-voltage insulation and mechanical protection system. Self-healing trigger units 8 are evenly spaced along the cable axis between the non-magnetic armor layer 6 and the outer sheath 7. Each unit includes a fixed bracket 81 fixed to the outer surface of the non-magnetic armor layer 6, a piercing needle 82 mounted on the fixed bracket 81 and facing the inner wall of the outer sheath 7, and a sealed storage cavity 83 fitted to the outer surface of the non-magnetic armor layer 6 and filled with moisture-curing polyurethane foam. A preset gap of 0.2–0.5 mm is maintained between the tip of the piercing needle 82 and the inner wall of the outer sheath 7. When the outer sheath 7 is damaged by external force, the inner wall of the outer sheath 7 at the damaged point deforms towards the non-magnetic armor layer 6, thereby contacting and pushing the tip of the piercing needle 82 to pierce the sealed storage cavity 83 and release the repair agent. After the repair agent comes into contact with external moisture, it foams and solidifies to seal the damage. This triggering and repair process does not rely on any external power source or complex intelligent monitoring equipment, and is achieved by relying entirely on the cable's own structure to achieve passive triggering. The pre-set gap between the puncture needle 82 and the inner wall of the outer sheath 7 ensures that the original electric field distribution of the cable is not changed under normal operating conditions, and does not interfere with the insulation strength of the 27.5kV high-voltage system, meeting the electrical safety standards for railway high-voltage cables. When the outer sheath 7 is damaged, it can actively seal the leak without manual intervention, effectively preventing insulation breakdown and partial discharge faults caused by damage expansion, significantly reducing the risk of sudden power outages, and ensuring the continuous and stable operation of the traction power supply system. The non-magnetic aluminum wire armor structure effectively avoids eddy current losses generated by single-phase power supply in electrified railways. The outer sheath 7 is made of low-smoke halogen-free flame-retardant material with strong anti-aging and anti-corrosion capabilities. The repair materials are inexpensive and the process is simple, which can significantly reduce the frequency of manual inspections and the workload of emergency repairs, and significantly reduce the operation and maintenance investment throughout the cable's life cycle.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A 27.5kV electrified railway power cable with self-healing capability, characterized in that, From the inside out, it includes a copper conductor (1), a conductor shielding layer (2), an XLPE insulation layer (3), an insulation shielding layer (4), a buffer water-blocking layer (5), a non-magnetic armor layer (6), an outer sheath (7), and a self-healing triggering unit (8) disposed between the non-magnetic armor layer (6) and the outer sheath (7); The self-healing trigger unit (8) includes a fixed bracket (81), a puncture needle (82), and a sealed storage cavity (83); the fixed bracket (81) is fixed to the outer surface of the non-magnetic armor layer (6), the puncture needle (82) is disposed on the fixed bracket (81) and faces the inner wall of the outer sheath (7), and the sealed storage cavity (83) is attached to the outer surface of the non-magnetic armor layer (6) and is filled with a repair agent; there is a preset gap between the tip of the puncture needle (82) and the inner wall of the outer sheath (7); When the outer sheath (7) is damaged, the inner wall of the outer sheath (7) at the damaged point deforms towards the non-magnetic armor layer (6), thereby contacting and pushing the tip of the piercing needle (82), causing the piercing needle (82) to pierce the sealed storage cavity (83) to release the repair agent. The repair agent solidifies after contacting external moisture to seal the damage.

2. The 27.5kV electrified railway power cable with self-healing capability according to claim 1, characterized in that, The self-healing trigger unit (8) is arranged at equal intervals along the cable axis, with an axial interval of 1.5 meters, and two units are evenly distributed in the circumferential direction.

3. The 27.5kV electrified railway power cable with self-healing capability according to claim 1, characterized in that, The preset gap between the puncture needle (82) and the inner wall of the outer sheath (7) is 0.2 to 0.5 mm; the repair agent filled in the sealed storage cavity (83) is a moisture-curing polyurethane foam colloid material.

4. The 27.5kV electrified railway power cable with self-healing capability according to claim 1, characterized in that, The non-magnetic armor layer (6) is made of non-magnetic aluminum wire armor, and the armor pitch is 8 to 12 times the outer diameter of the cable; the buffer water-blocking layer (5) is made of semi-conductive buffer water-blocking tape with overlapping wrapping, and the overlap rate is 20% to 30%; the outer sheath (7) is made of low smoke halogen-free flame-retardant polyolefin material.

5. The 27.5kV electrified railway power cable with self-healing capability according to claim 1, characterized in that, The copper conductor (1) is a multi-strand oxygen-free copper wire tightly twisted structure with the twisting direction to the right and the compaction coefficient not less than 0.9; the conductor shielding layer (2) and the insulating shielding layer (4) are both semi-conductive cross-linked polyethylene materials; the XLPE insulating layer (3) is a 27.5kV medium voltage cable special cross-linked polyethylene material; the conductor shielding layer (2), the XLPE insulating layer (3) and the insulating shielding layer (4) are a three-layer co-extruded integral structure.

6. The method for preparing a 27.5kV electrified railway power cable with self-healing capability as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare copper conductor (1) by tightly stranding multiple strands of oxygen-free copper wire. After stranding, straighten, polish and ultrasonically clean the surface of copper conductor (1). Step 2: Using a three-layer co-extrusion process, a conductor shielding layer (2), an XLPE insulation layer (3), and an insulation shielding layer (4) are sequentially coated onto the copper conductor (1), followed by cross-linking reaction and cooling for shaping; Step 3: Cover the insulating shielding layer (4) with a buffer water-blocking layer (5); Step 4: Armor the outside of the buffer water-blocking layer (5) to form a non-magnetic armor layer (6); Step 5: Install the self-healing trigger unit (8) at intervals along the cable axis on the outer surface of the non-magnetic armor layer (6), with the piercing needle (82) facing outwards and the sealed storage cavity (83) attached to the outer wall of the non-magnetic armor layer (6). The sealed storage cavity (83) is filled with a moisture-curing repair agent. Step 6: Extrude an outer sheath (7) over the non-magnetic armor layer (6) on which the self-healing trigger unit (8) is installed, so that the piercing needle (82) and the inner wall of the outer sheath (7) maintain a preset gap.

7. The method for preparing a 27.5kV electrified railway power cable with self-healing capability according to claim 6, characterized in that, In step one, the copper conductor (1) is twisted in the right direction, and the compression coefficient is not less than 0.9; In step two, the preheating temperature of the copper conductor (1) is 80-100℃, the temperature of each section of the extruder is 110-140℃, the temperature of the crosslinking tube is 180-200℃, the crosslinking pressure is 0.6-0.8MPa, and the degree of crosslinking of the XLPE insulation layer (3) after crosslinking is not less than 92%.

8. The method for preparing a 27.5kV electrified railway power cable with self-healing capability according to claim 6, characterized in that, In step three, the buffer water-blocking layer (5) is wrapped with overlapping semi-conductive buffer water-blocking tape, with an overlap rate of 20% to 30%.

9. The method for preparing a 27.5kV electrified railway power cable with self-healing capability according to claim 6, characterized in that, In step four, the armor is made of non-magnetic aluminum wire, and the armor pitch of the non-magnetic armor layer (6) is 8 to 12 times the outer diameter of the cable.

10. The method for preparing a 27.5kV electrified railway power cable with self-healing capability according to claim 6, characterized in that, In step five, the self-healing trigger unit (8) is installed at 1.5-meter intervals along the cable axis, with two units evenly distributed in the circumferential direction; In step six, the outer sheath (7) is extruded with low-smoke halogen-free flame-retardant polyolefin material at an extrusion temperature of 160-190°C. The preset gap between the puncture needle (82) and the inner wall of the outer sheath (7) is 0.2-0.5 mm. The repair agent filled in the sealed storage cavity (83) is moisture-curing polyurethane foam colloid material.

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