Railway digital signal cable with self-monitoring function

Abstract

The application relates to the technical field of communication cables, and particularly discloses a railway digital signal cable with a self-monitoring function, which comprises a cable core, a composite shielding layer and a self-monitoring layer arranged in sequence from inside to outside; the composite shielding layer is wrapped outside the cable core and comprises a first shielding layer, a second shielding layer and a third shielding layer arranged in sequence from inside to outside; the first shielding layer is a metal plastic composite tape wrapping layer and is used for reflecting low-frequency electromagnetic interference; the second shielding layer is a metal foil layer with a microporous structure; the third shielding layer is a semi-conductive polymer layer or a semi-conductive composite material layer; the self-monitoring layer comprises at least two sensing monitoring lines arranged outside the third shielding layer along the cable axial direction, and the sensing monitoring lines and the third shielding layer form a distributed parameter sensor. Therefore, the railway digital signal cable has high shielding efficiency, environmental corrosion resistance, real-time self-monitoring capability and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of communication cable technology, and more specifically to a railway digital signal cable with self-monitoring function. Background Technology

[0002] Railway digital signal cables, as the core transmission medium of rail transit signaling systems, are mainly used to transmit railway digital signals, audio signals, and control commands. Their transmission stability, anti-interference capabilities, and ease of maintenance directly affect the safety and punctuality of train operations, making them a crucial link in ensuring the normal operation of high-speed railways and urban rail transit.

[0003] In recent years, with the rapid development of high-speed railways and urban rail transit, train speeds have significantly increased and operating density has risen dramatically. The electromagnetic environment along railway lines has become increasingly complex, placing higher demands on cable maintenance efficiency and preventative maintenance capabilities. Traditional railway digital signal cables typically employ a single-layer aluminum-plastic tape or aluminum tape metal shielding structure to resist external electromagnetic interference. Regarding cable monitoring, current technologies mainly rely on manual inspection or offline testing methods. This involves periodically checking the cable's integrity using a dedicated time-domain reflectometer or insulation tester after installation. However, this method is not only inefficient but also unable to provide real-time warnings when localized damage, insulation aging, or moisture absorption occurs, making it difficult to meet the maintenance needs under complex operating conditions.

[0004] Analysis reveals the following main technical defects in existing railway digital signal cables used in practical applications:

[0005] (1) Insufficient electromagnetic interference resistance. Existing metal shielding layers have a good shielding effect against low-frequency magnetic field interference, but in high-frequency bands or strong electromagnetic field environments, especially under the complex high-order harmonic interference of traction current in electrified railways, the shielding effectiveness drops significantly, making it difficult to control the crosstalk attenuation between line groups within the ideal range under high-frequency conditions, which in turn affects the transmission quality of high-speed signals such as train control systems and easily leads to signal distortion or misjudgment.

[0006] (2) The shielding layer is prone to corrosion and is discontinuous. Traditional shielding layers mostly adopt a longitudinal wrapping or braided structure of metal strips. After the cable is bent, laid, or operated outdoors for a long time, gaps, oxidation or loosening are likely to appear at the longitudinal wrapping joints of the shielding layer, which will increase the surface impedance of the shielding layer, cause the continuity of electromagnetic shielding to fail, further reduce the anti-interference ability, and shorten the service life of the cable.

[0007] (3) Lack of real-time self-monitoring capability. During long-term operation, the insulation layer of cables may gradually decrease in insulation strength due to electrochemical corrosion, thermal aging, water tree effect, or mechanical damage, and may even lead to grounding faults. Existing cables are "dumb devices" and cannot sense their own physical state, lacking built-in real-time monitoring methods. Once a fault occurs, maintenance personnel must use external instruments for offline troubleshooting, which is not only time-consuming and labor-intensive, but also has low fault location accuracy, seriously affecting the maintenance efficiency and traffic safety of railway transportation, and is not conducive to achieving preventive maintenance.

[0008] (4) It is difficult to balance mechanical strength and flexibility. In order to improve the anti-interference ability, traditional technologies often adopt the method of simply increasing the thickness of the shielding layer, which leads to an increase in the outer diameter of the cable and a decrease in flexibility, which increases the difficulty of laying in tunnels, bridges or narrow spaces, and also increases the laying cost and construction workload.

[0009] In summary, existing railway digital signal cables have significant shortcomings in terms of anti-interference performance, structural reliability, intelligent monitoring capabilities, and mechanical performance. There is an urgent need to propose a cable structure that can balance high shielding effectiveness, environmental corrosion resistance, real-time self-monitoring capabilities, and excellent mechanical properties. Summary of the Invention

[0010] The purpose of this invention is to provide a railway digital signal cable with self-monitoring function, which combines high shielding effectiveness, environmental corrosion resistance, real-time self-monitoring capability, and excellent mechanical properties.

[0011] This invention is achieved through the following technical solution:

[0012] A railway digital signal cable with self-monitoring function includes a cable core, a composite shielding layer and a self-monitoring layer arranged sequentially from the inside to the outside;

[0013] The composite shielding layer covers the outside of the cable core and includes a first shielding layer, a second shielding layer, and a third shielding layer arranged sequentially from the inside out. The first shielding layer is a metal-plastic composite tape wrapping layer used to reflect low-frequency electromagnetic interference. The second shielding layer is a metal foil layer with a microporous structure, which is configured to generate resonance in a predetermined high-frequency band to absorb high-frequency electromagnetic interference energy. The third shielding layer is a semi-conductive polymer layer or a semi-conductive composite material layer used to smooth the residual electric field and provide an equipotential reference surface.

[0014] The self-monitoring layer includes at least two inductive monitoring lines arranged along the cable axis outside the third shielding layer. The inductive monitoring lines and the third shielding layer form a distributed parameter sensor. The inductive monitoring lines are communicatively connected to an online monitoring unit, which monitors the insulation state changes between the third shielding layer and the cable core through the time domain reflection principle, and locates the fault point.

[0015] In one possible design, the micropore structure parameters of the second shielding layer are: pore size 0.1mm-0.3mm, pore density 50 pores / cm³. 2 -200 pieces / cm 2 The microporous structure is formed by chemical etching, laser drilling or mechanical perforation.

[0016] In one possible design, the second shielding layer is made of microporous copper foil or microporous nickel foil, which is wrapped around the outside of the first shielding layer in a longitudinal wrapping manner, and the longitudinal wrapping overlap is electrically continuous by welding or crimping.

[0017] In one possible design, the volume resistivity of the third shielding layer is 10. 4 Ω.cm-10 6 The third shielding layer is Ω.cm thick and 0.3mm-0.8mm thick. The third shielding layer is tightly bonded to the second shielding layer by hot pressing or extrusion.

[0018] In one possible design, the number of sensing monitoring lines is two, which are arranged symmetrically and parallel to each other along the cable axis. The sensing monitoring lines are selected from metallized conductive fiber bundles, flexible copper braided tapes, or tinned copper stranded wires, and have a diameter of 0.5mm-0.8mm.

[0019] In one possible design, the self-monitoring layer further includes a water-resistant yarn layer woven or wrapped around the outside of the sensing monitoring line, the water-resistant yarn layer being used to press the sensing monitoring line tightly against the surface of the third shielding layer.

[0020] In one possible design, the cable core includes multiple shielded four-wire groups and multiple unshielded four-wire groups, each group being twisted at a predetermined pitch, and the cable core is wrapped with at least one layer of polyester tape, the overlap rate of which is ≥15%.

[0021] In one possible design, the first shielding layer is a single-sided self-adhesive aluminum-plastic composite tape with a thickness of 0.06mm-0.08mm and a wrapping overlap rate of ≥25%; two soft copper drain lines are placed inside the first shielding layer.

[0022] In one possible design, the insulated single wire in the cable core has a three-layer co-extruded structure of sheath-foam-sheath, including an inner sheath, a foam layer and an outer sheath layer that are sequentially wrapped around the outside of the conductor, and a high dielectric constant ceramic film is coated on the surface of the outer sheath layer.

[0023] The high dielectric constant ceramic film is a barium titanate ceramic film with a thickness of 5μm-10μm and a thickness deviation of <±0.5μm. The barium titanate ceramic film is formed by precision coating, thermal curing or ultraviolet curing process, and its dielectric constant fluctuation rate in the 1MHz-10GHz frequency band is ≤3%.

[0024] In one possible design, the railway digital signal cable also includes an inner lining layer, a pressure-resistant armor layer, and an outer sheath arranged sequentially from the inside to the outside of the self-monitoring layer; the pressure-resistant armor layer is a double-layer galvanized steel strip gap wrapping structure with a gap ratio ≤50%; the outer sheath is environmentally friendly linear low-density polyethylene or low-smoke halogen-free flame-retardant polyolefin.

[0025] The advantages of this invention over the prior art are as follows:

[0026] The above technical solution, through the gradient composite shielding structure of "reflection-absorption-smoothing", especially by utilizing the resonant absorption mechanism of microporous metal foil layer, effectively solves the problem of the reduced shielding effectiveness of traditional single-layer metal shielding layer in high-frequency band and strong electromagnetic field environment. It can specifically suppress the high-order harmonic interference of complex traction current in electrified railways, ensure the transmission quality of high-speed signals such as train control system, and avoid signal distortion or misjudgment.

[0027] The tight bonding structure of the second and third shielding layers, along with the protective coverage of the metal foil layer by the semi-conductive layer, effectively reduces gaps, oxidation, or loosening of the shielding layer caused by bending, installation, or long-term operation. This ensures low-impedance electrical continuity on the shielding surface and extends the cable's service life in complex outdoor environments. By embedding the distributed parameter sensor, composed of the inductive monitoring line and the third shielding layer, into the cable body, continuous sensing of insulation state changes between the cable core and the shielding layer is possible without external monitoring equipment. Combined with the time-domain reflectometry principle, an early warning can be issued when insulation degradation progresses to the point where detectable changes in distributed parameters occur (e.g., insulation resistance drops below 80% of its initial value or local capacitance changes exceed 5%), and the fault location can be quickly and accurately determined. This significantly improves maintenance efficiency, reduces troubleshooting time and costs, facilitates preventative maintenance in railway systems, and ensures safe train operation.

[0028] The third shielding layer, serving as an equipotential reference surface, not only enhances the shielding effect but also provides a stable electrical reference for accurate monitoring of the inductive monitoring line. This creates functional synergy between the shielding and monitoring structures, improving the overall operational reliability of the cable system. Therefore, by replacing the traditional thick single-layer metal shielding with a multi-layer thin composite shielding structure, higher shielding efficiency is achieved while effectively controlling the cable's outer diameter and maintaining good flexibility. This facilitates laying in complex environments such as tunnels, bridges, and confined spaces, reducing laying workload and construction costs, and also lowering the risk of cable damage during installation. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0030] Figure 1 This is a cross-sectional structural diagram of a railway digital signal cable with self-monitoring function provided by the present invention in one embodiment;

[0031] Figure 2 This is a schematic diagram of the cable core in one embodiment of a railway digital signal cable with self-monitoring function provided by the present invention;

[0032] Figure 3 This is a schematic diagram of the composite shielding layer in one embodiment of a railway digital signal cable with self-monitoring function provided by the present invention;

[0033] Figure 4 This is a microstructure diagram of the second shielding layer (microporous copper foil) in a railway digital signal cable with self-monitoring function provided by the present invention;

[0034] Figure 5 This is a schematic diagram of the principle of a railway digital signal cable with self-monitoring function provided by the present invention.

[0035] The markings and corresponding component names in the attached diagram are as follows: 1-Cable core, 10-Conductor, 101-Inner sheath, 102-Foaming layer, 103-Outer sheath, 104-Barium titanate ceramic membrane, 11-Shielded four-wire group, 12-Unshielded four-wire group, 13-Polyester tape, 2-Composite shielding layer, 21-First shielding layer, 22-Second shielding layer, 23-Third shielding layer, 31-Induction monitoring line, 32-Water-blocking yarn layer, 4-Drainage line, 5-Inner lining layer, 6-Pressure-resistant armor layer, 7-Outer sheath. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that while the description of these embodiments is intended to aid in understanding the invention, it does not constitute a limitation thereof. The specific structural and functional details disclosed herein are only for describing exemplary embodiments of the invention. However, the invention can be embodied in many alternative forms and should not be construed as being limited to the embodiments described herein.

[0037] According to a first aspect of this disclosure, a railway digital signal cable with self-monitoring function is provided. Wherein, Figures 1 to 5 Specific embodiments thereof are shown.

[0038] See Figures 1 to 5 As shown, a railway digital signal cable with self-monitoring function includes a cable core 1, a composite shielding layer 2, and a self-monitoring layer arranged sequentially from the inside to the outside. The composite shielding layer 2 covers the outside of the cable core 1 and includes a first shielding layer 21, a second shielding layer 22, and a third shielding layer 23 arranged sequentially from the inside to the outside. The first shielding layer 21 is a metal-plastic composite tape wrapping layer used to reflect low-frequency electromagnetic interference. The second shielding layer 22 is a metal foil layer with a microporous structure, which is configured to generate resonance in a predetermined high-frequency band to absorb high-frequency electromagnetic interference energy. The third shielding layer 23 is a semi-conductive polymer layer or a semi-conductive composite material layer used to smooth the residual electric field and provide an equipotential reference surface. The self-monitoring layer includes at least two inductive monitoring lines 31 arranged along the cable axis outside the third shielding layer 23. The inductive monitoring lines 31 and the third shielding layer 23 form a distributed parameter sensor. The inductive monitoring lines 31 are communicatively connected to an online monitoring unit to monitor the insulation state changes between the third shielding layer 23 and the cable core 1 through the time-domain reflectometry principle and locate the fault point.

[0039] When the cable is in normal operation, the railway digital signals, audio signals, and control commands transmitted inside the cable core 1 propagate through the insulated single wire. Simultaneously, the complex electromagnetic environment outside the cable, especially high-frequency electromagnetic interference such as high-order harmonics of the traction current generated by electrified railways, acts on the cable surface. This electromagnetic interference first reaches the first shielding layer 21 of the composite shielding layer 2. This first shielding layer 21 is a metal-plastic composite tape wrapping layer, utilizing the low-frequency reflection characteristics of metallic materials to reflect most of the low-frequency electromagnetic interference energy back to the external environment, achieving basic shielding.

[0040] High-frequency electromagnetic interference penetrating the first shielding layer 21 continues to propagate inward, reaching the second shielding layer 22. The second shielding layer 22 is a metal foil layer with a microporous structure, which is pre-configured to generate a resonant effect in a specific high-frequency band (e.g., the typical frequency band of high-order harmonics in electrified railways). When the frequency of the high-frequency electromagnetic interference matches the resonant frequency of the microporous structure, the second shielding layer 22 converts the electromagnetic interference energy into heat dissipation, thereby selectively absorbing the high-frequency interference component and preventing it from entering the cable. After reflection by the first shielding layer 21 and absorption by the second shielding layer 22, the residual weak electromagnetic field signal continues to propagate inward, reaching the third shielding layer 23. The third shielding layer 23 is made of a semi-conductive polymer or semi-conductive composite material, and its uniform and continuous structure can smooth the non-uniform distribution of the residual electric field while forming a stable equipotential reference surface. This equipotential reference surface further weakens the coupling effect of the residual electric field on the cable core 1 and provides a stable electrical reference for the subsequent self-monitoring layer. Through the sequential action of the three shielding structures described above, the composite shielding layer 2 forms a gradient shielding effect of "low-frequency reflection - high-frequency absorption - residual smoothing", ensuring the electromagnetic purity of the transmission environment inside the cable core 1 and guaranteeing low-distortion and low-error transmission of high-speed signals.

[0041] During normal cable operation, at least two inductive monitoring lines 31 located outside the third shielding layer 23 are grounded through a terminating matching resistor, maintaining equipotential with the third shielding layer 23. At this time, a stable distributed parameter system is formed between the inductive monitoring lines 31, the third shielding layer 23, and the cable core 1. Its equivalent insulation resistance and distributed capacitance are both within the preset reference value range, and the online monitoring unit outputs no abnormal signals.

[0042] When the cable undergoes long-term operation, factors such as electrochemical corrosion, thermal aging, water treeing, or mechanical damage cause localized degradation of the insulation medium between the cable core 1 and the third shielding layer 23 (e.g., decreased insulation resistance, abnormally increased distributed capacitance), a characteristic abrupt change occurs in the distributed parameters at the fault point. This abrupt change alters the impedance matching state between the inductive monitoring line 31 and the third shielding layer 23 near the fault point.

[0043] At this time, the online monitoring unit, connected to the inductive monitoring line 31, injects a high-frequency, low-voltage pulse signal into the inductive monitoring line 31. This pulse signal propagates along the axial direction of the cable. When the pulse signal reaches the fault point, due to the impedance mismatch at the fault point, the pulse signal generates a reflected echo, which returns to the online monitoring unit along the inductive monitoring line 31.

[0044] The online monitoring unit records the time difference between the transmitted pulse and the received reflected pulse in real time. Based on the known propagation speed of the pulse signal in the inductive monitoring line 31, it calculates the distance from the transmitter to the fault point using a time-domain reflection algorithm, thus achieving fault location with meter-level accuracy. Maintenance personnel can quickly locate and handle faults based on the location information without having to conduct offline troubleshooting of the entire cable.

[0045] The above technical solution, through the gradient composite shielding structure of "reflection-absorption-smoothing", especially by utilizing the resonant absorption mechanism of microporous metal foil layer, effectively solves the problem of the reduced shielding effectiveness of traditional single-layer metal shielding layer in high-frequency band and strong electromagnetic field environment. It can specifically suppress the high-order harmonic interference of complex traction current in electrified railways, ensure the transmission quality of high-speed signals such as train control system, and avoid signal distortion or misjudgment.

[0046] The tight bonding structure of the second shielding layer 22 and the third shielding layer 23, along with the protective covering of the metal foil layer by the semi-conductive layer, effectively reduces gaps, oxidation, or loosening of the shielding layer caused by bending, installation, or long-term operation. This ensures low-impedance electrical continuity on the surface of the shielding layer and extends the cable's service life in complex outdoor environments. By embedding the distributed parameter sensor, composed of the inductive monitoring line 31 and the third shielding layer 23, into the cable body, continuous sensing of insulation state changes between the cable core 1 and the shielding layer is possible without external monitoring equipment. Combining the time-domain reflectometry principle, early warnings can be issued in the early stages of insulation degradation (before it develops into a short circuit or open circuit fault), and the fault location can be quickly and accurately determined. This significantly improves maintenance efficiency, reduces fault diagnosis time and costs, facilitates preventative maintenance of the railway system, and ensures safe train operation.

[0047] The third shielding layer 23, serving as an equipotential reference surface, not only enhances the shielding effect but also provides a stable electrical reference for the accurate monitoring of the inductive monitoring line 31. This creates functional synergy between the shielding and monitoring structures, thereby improving the overall operational reliability of the cable system. Therefore, by replacing the traditional thick single-layer metal shielding with a multi-layer thin composite shielding structure, higher shielding efficiency is achieved while effectively controlling the cable's outer diameter and maintaining good flexibility. This facilitates laying in complex environments such as tunnels, bridges, and confined spaces, reducing laying workload and construction costs, and also lowering the risk of cable damage during installation.

[0048] It should be noted that directional terms such as "inner" and "outer" refer to "inner" and "outer" relative to the outline of the component; "inner" refers to the direction towards the component, and "outer" refers to the direction away from it. Furthermore, terms such as "first" and "second" are used to distinguish one element from another and do not indicate sequence or importance. Also, in the accompanying drawings, the same reference numerals in different drawings represent the same element. It should be noted that "and / or" in the text refers to A and / or B, indicating that there are three possible scenarios: only A, only B, or both A and B. Conversely, " / and" in the text refers to A and B, indicating that there are two possible scenarios: only A and both A and B.

[0049] In one embodiment provided in this disclosure, the micropore structure parameters of the second shielding layer 22 are: pore diameter 0.1mm-0.3mm, pore density 50 pores / cm³. 2 -200 pieces / cm 2 The microporous structure is formed through chemical etching, laser drilling, or mechanical perforation. Under these aperture and density conditions, the microporous structure can form a resonant unit that matches the target high-frequency interference frequency, thereby efficiently converting the high-frequency electromagnetic interference energy penetrating the first shielding layer 21 into heat dissipation and significantly improving the absorption capability of higher harmonics. If the aperture is too large or the aperture density is too low, the resonant frequency will shift, and the absorption efficiency will decrease; if the aperture is too small or the aperture density is too high, additional high-frequency insertion loss may be introduced. Therefore, the above parameter range achieves an optimized balance between high-frequency absorption performance and signal transmission quality.

[0050] Microporous structures are formed through chemical etching, laser drilling, or mechanical perforation. These processes are mature metal processing methods that can precisely control the pore size and pore density in large-scale production, ensuring the uniformity and consistency of the microporous structure, thereby ensuring that mass-produced cable products have stable and reliable high-frequency shielding performance.

[0051] In one embodiment provided in this disclosure, the second shielding layer 22 is made of microporous copper foil or microporous nickel foil, which is wrapped around the outside of the first shielding layer 21 in a longitudinal wrapping manner, and the longitudinal wrapping overlap is electrically continuous through welding or crimping. Longitudinally wrapping the outside of the first shielding layer 21 allows the metal foil layer to continuously cover the cable axis, which helps maintain the overall uniformity of the shielding layer. Simultaneously, the electrical continuity achieved through welding or crimping at the longitudinal wrapping overlap solves the problem of gaps, oxidation, or loosening that easily occur at the longitudinal wrapping overlap of traditional shielding layers due to bending, installation, or long-term operation. This ensures low-impedance electrical continuity on the surface of the shielding layer and avoids a decrease in anti-interference capability due to shielding discontinuity. Furthermore, both copper foil and nickel foil have good conductivity and corrosion resistance, with nickel foil performing particularly well in humid or chemically corrosive environments. The appropriate foil can be flexibly selected according to the application scenario, thereby improving the stability of the high-frequency shielding effect and the service life of the cable, ensuring the long-term reliable operation of railway digital signal cables in complex outdoor environments.

[0052] In one embodiment provided in this disclosure, the volume resistivity of the third shielding layer 23 is 10. 4 Ω.cm-10 6 The third shielding layer 23, with a volume resistivity of Ω·cm and a thickness of 0.3mm-0.8mm, is tightly bonded to the second shielding layer 22 via hot-pressing or extrusion. This volume resistivity range allows the third shielding layer 23 to be in a semi-conductive state, serving as an equipotential reference surface to smooth residual electric fields and suppress localized electrical stress concentration, while avoiding the risk of short circuits between it and the cable core 1 due to excessive conductivity. Simultaneously, this thickness range ensures that the third shielding layer 23 possesses sufficient mechanical strength and buffering capacity, effectively protecting the microporous structure of the inner second shielding layer 22 from external force damage or oxidation. The tight bonding of the third shielding layer 23 and the second shielding layer 22 via hot-pressing or extrusion creates a seamless, continuous electrical contact between the two layers, avoiding interface reflections and partial discharges caused by interlayer separation, and further enhancing the overall mechanical stability of the shielding structure.

[0053] In one embodiment provided in this disclosure, there are two inductive monitoring lines 31, which are symmetrically and parallelly arranged along the cable axis. The inductive monitoring lines 31 are selected from metallized conductive fiber bundles, flexible copper braided tapes, or tinned copper stranded wires, with a diameter of 0.5mm-0.8mm. The symmetrical parallel arrangement enables the two inductive monitoring lines 31 to form a uniform and consistent distributed parameter structure with the third shielding layer 23, which is beneficial for maintaining a stable equipotential state during normal operation. At the same time, it generates a symmetrical and measurable impedance change when a fault occurs, which facilitates the online monitoring unit to accurately capture the reflected signal. The redundant configuration of the two monitoring lines can also mutually verify each other, reducing the risk of false alarms caused by the breakage or poor contact of a single monitoring line. The inductive monitoring lines 31 are selected from metallized conductive fiber bundles, flexible copper braided tapes, or tinned copper stranded wires. All of the above materials have good conductivity and flexibility, and can be bent and laid together with the cable without being easily broken. The diameter is limited to 0.5mm-0.8mm, ensuring that the monitoring line has sufficient current-carrying capacity and mechanical strength to stably transmit high-frequency pulse signals, while avoiding increasing the cable's outer diameter or reducing its flexibility due to excessive diameter. This allows the inductive monitoring line 31 to operate stably over long periods, achieving sensitive response to changes in insulation condition, and, combined with the time-domain reflectometry principle, achieving meter-level accuracy in fault location, effectively improving the cable's self-monitoring capabilities and ease of maintenance.

[0054] In one embodiment of this disclosure, the self-monitoring layer further includes a water-blocking yarn layer 32 woven or wrapped around the outside of the inductive monitoring line 31. The water-blocking yarn layer 32 is used to press the inductive monitoring line 31 tightly against the surface of the third shielding layer 23. Through the radial pressing action of the water-blocking yarn layer 32, a stable and low-impedance electrical contact is formed between the inductive monitoring line 31 and the third shielding layer 23, preventing the inductive monitoring line 31 from loosening or detaching from the surface of the third shielding layer 23 during cable bending, vibration, or temperature changes. This ensures the consistency and reliability of the distributed parameter sensor and prevents monitoring signal distortion or abnormal reflection caused by poor contact. At the same time, the water-blocking yarn layer 32 itself has the characteristic of swelling when exposed to water. It can quickly absorb the seeping water and expand to seal it when the cable sheath is damaged, preventing the water from spreading along the cable axis, effectively delaying the process of insulation dampness and aging, and protecting the internal shielding structure and cable core 1 from long-term water erosion.

[0055] In one embodiment provided in this disclosure, the cable core 1 includes multiple shielded four-wire groups 11 and multiple unshielded four-wire groups 12. Each group is twisted at a predetermined pitch. The cable core 1 is wrapped with at least one layer of polyester tape 13, with an overlap rate of ≥15%. By reasonably configuring the number and twisting pitch of the shielded and unshielded groups, the electromagnetic coupling between different groups can be effectively reduced, and the crosstalk attenuation index between groups can be optimized. Especially in high-density signal transmission scenarios, it can reduce interference between adjacent groups. The cable core 1 is wrapped with at least one layer of polyester tape 13, with an overlap rate of ≥15%. This wrapping structure can tightly bind each group, ensuring the roundness and structural stability of the cable core 1, and preventing the cable core 1 from loosening or deforming during the subsequent shielding layer fabrication and laying process. At the same time, the polyester tape 13 with an overlap rate of ≥15% can form a continuous and uniform binding force, further improving the mechanical strength of the cable core 1 and providing a flat and stable base for the uniform coverage of the outer composite shielding layer 2.

[0056] In one embodiment provided in this disclosure, the first shielding layer 21 is a single-sided self-adhesive aluminum-plastic composite tape with a thickness of 0.06mm-0.08mm and a wrapping overlap rate of ≥25%. Two soft copper drain wires 4 are sequentially placed inside the first shielding layer 21. The self-adhesive design allows the wrapping layer to self-adhere at the overlap, forming a continuous and compact metal shielding layer, effectively preventing warping or slippage at the overlap due to bending or laying. The 0.06mm-0.08mm thickness controls the cable outer diameter while ensuring sufficient mechanical strength and shielding effectiveness. The overlap rate of ≥25% ensures the electrical continuity of the shielding layer and radial moisture-proof sealing performance, preventing moisture from seeping into the cable core 1 along the overlap gap. Simultaneously, the two sequentially placed soft copper drain wires 4 inside the first shielding layer 21 provide a low-impedance discharge path when induced charge or fault current is generated, quickly guiding the charge to the grounding terminal, preventing charge accumulation from damaging the insulation layer, and reducing interference to signal transmission caused by the potential rise of the shielding layer. Thus, the first shielding layer 21 not only achieves the dual functions of low-frequency reflection shielding and radial moisture protection, but also has reliable charge discharge capability, providing a good foundation for the stable operation of the subsequent high-frequency absorption layer and self-monitoring layer.

[0057] In one embodiment provided in this disclosure, the insulated single wire in the cable core 1 has a three-layer co-extruded structure of sheath-foam-sheath, including an inner sheath layer 101, a foam layer 102, and an outer sheath layer 103 sequentially covering the outside of the conductor 10, and a high dielectric constant ceramic film is coated on the surface of the outer sheath layer 103; wherein, the high dielectric constant ceramic film is a barium titanate ceramic film 104 with a thickness of 5μm-10μm and a film thickness deviation of <±0.5μm. The barium titanate ceramic film 104 is formed by precision coating, thermosetting, or ultraviolet curing process, and its dielectric constant fluctuation rate in the 1MHz-10GHz frequency band is ≤3%.

[0058] Barium titanate, with its high dielectric constant, can homogenize the electric field distribution on the surface of conductor 10 after being coated onto the outer sheath 103, buffering electrical stress concentration and thus reducing the risk of partial discharge and improving insulation reliability. The barium titanate ceramic film 104, formed through precision coating, thermosetting, or UV curing processes, exhibits a dielectric constant fluctuation rate of ≤3% across a wide frequency band of 1MHz-10GHz. This means that the dielectric properties of the insulation structure remain highly stable during high-frequency signal transmission, effectively reducing signal attenuation and transmission delay, and improving signal fidelity. It is particularly suitable for transmission scenarios with high data rates and high stability requirements, such as high-speed railway train control systems. The extremely thin ceramic film thickness and strict thickness deviation control ensure that its impact on the cable's outer diameter and flexibility is negligible, while ensuring consistent electrical performance throughout the entire cable length. This design improves the high-frequency transmission quality of the cable from the basic level of the insulated single wire, forming a synergistic effect of "internal stability and external protection" with the electromagnetic protection function of the composite shielding layer 2, comprehensively guaranteeing the transmission stability and reliability of railway digital signal cables. It should be noted that precision coating, thermosetting, or UV curing processes are all existing technologies.

[0059] In one embodiment provided in this disclosure, the railway digital signal cable further includes, from the inside out, an inner liner 5, a pressure-resistant armor layer 6, and an outer sheath 7, sequentially disposed outside the self-monitoring layer; the pressure-resistant armor layer 6 is a double-layer galvanized steel strip gap-wrapped structure with a gap ratio ≤50%; the outer sheath 7 is environmentally friendly linear low-density polyethylene or low-smoke halogen-free flame-retardant polyolefin. The inner liner 5, as a buffer layer, effectively isolates the mechanical friction and pressure between the self-monitoring layer and the outer armor layer, protecting the integrity of the internal induction monitoring line 31 and the shielding structure. The pressure-resistant armor layer 6, with its double-layer galvanized steel strip gap-wrapped structure and a gap ratio ≤50%, provides sufficient compressive and tensile mechanical strength while maintaining the cable's flexibility, avoiding bending difficulties caused by excessively thick armor layers or fully enclosed structures. This facilitates laying in complex environments such as tunnels and bridges, and the gap-wrapped structure promotes relative sliding between the steel strips when the cable bends, reducing the risk of laying damage. The outer sheath 7 is made of environmentally friendly linear low-density polyethylene or low-smoke halogen-free flame-retardant polyolefin. The former has good weather resistance, abrasion resistance, and UV resistance, making it suitable for long-term outdoor operation; the latter has low smoke emission, no halogen release, and low toxicity during combustion, meeting the stringent standards for fire safety and environmental protection in rail transit. This layered structure ensures the cable's mechanical durability under complex laying environments and long-term operating conditions, while also considering ease of construction and safety and environmental requirements, providing reliable external protection for the stable operation of the internal shielding layer and self-monitoring layer.

[0060] Example 1

[0061] This embodiment provides a 24-core railway digital signal cable, suitable for conventional high-speed railways and urban rail transit sections. Its specific production process and parameters are as follows, with strict quality control at each stage to ensure the product meets design requirements.

[0062] 1. Preparation of conductor 10

[0063] Conductor 10 is made of annealed soft copper single wire conforming to the requirements of GB / T 3956 standard, with a nominal diameter of 1.0 mm and a tolerance controlled within ±0.003 mm.

[0064] 2. Insulation extrusion and ceramic film coating

[0065] The three-layer co-extrusion process is adopted to complete the "skin-bubble-skin" three-layer insulation structure of the annealed conductor 10 in one pass through the three-layer co-extrusion die head.

[0066] For the insulated single wire used in shielded four-wire group 11:

[0067] Inner skin layer: made of low-density polyethylene, tightly bonded to conductor 10, with a thickness controlled at 0.03mm;

[0068] Foaming layer 102: Made of high-density polyolefin foam, injected with nitrogen for foaming, with a foaming degree of ≤65%, fine and uniform cell structure, no broken or cross-foaming, and the thickness of foaming layer 102 is controlled between 0.85mm and 0.90mm.

[0069] Outer layer 103: Made of high-density polyethylene with a thickness of 0.18mm, the insulating surface is smooth and round, and can pass the 800N compression test.

[0070] For the insulated single wire used in unshielded four-wire group 12:

[0071] Inner skin layer: made of low-density polyethylene, tightly bonded to conductor 10, with a thickness of 0.03mm;

[0072] Foaming layer 102: Made of high-density foamed polyolefin, injected with nitrogen for foaming, with a foaming degree ≤60%, and the thickness of foaming layer 102 is controlled between 0.78mm and 0.83mm;

[0073] Outer skin layer 103: Made of high-density polyethylene with a thickness of 0.18mm, it can pass the 750N compression test.

[0074] Ceramic film coating: In the final stage of the extrusion process, barium titanate solution is coated onto the surface of the outer skin layer 103 using a precision spraying process. After coating, it is dried by hot air and cured by ultraviolet light to form a uniform barium titanate ceramic film 104 with a thickness of 8μm±2μm. The film thickness is monitored in real time using an online thickness gauge to ensure its uniformity and adhesion.

[0075] Coloring: After cooling, the insulated single wires are colored with four colors: red, green, white, and blue.

[0076] 3. Wire strand twisting

[0077] Four insulated single wires of different colors are twisted together at a predetermined pitch using a star twister to form a four-wire group.

[0078] 4. Internal shielding

[0079] For signal groups that require separate shielding (i.e., shielded four-wire group 11), internal shielding is performed after star twisting, and a drain wire is placed.

[0080] 5. Cable making

[0081] Four shielded four-wire groups 11 and two unshielded four-wire groups 12 are arranged in a concentric layer pattern of 1+5 and stranded into cable core 1 using a cabling machine, with the stranding pitch controlled between 600mm and 1000mm. Two layers of polyester tape 13 are used as a binding layer, with an overlap rate of ≥15%, to prevent cable core 1 from loosening.

[0082] 6. Construction of multi-layer composite shielding layer 2

[0083] First shielding layer 21 (wrapping): A single-sided self-adhesive aluminum-plastic composite tape with a nominal thickness of 0.07mm is wrapped around the outside of the polyester tape 13, with a wrapping overlap rate of ≥25%, and two soft copper drain wires 4 with a nominal diameter of 0.45mm are simultaneously placed in the same direction during the wrapping process.

[0084] The second shielding layer 22 (longitudinal wrapping): A layer of microporous copper foil with a nominal thickness of 0.05 mm is longitudinally wrapped around the outside of the first shielding layer 21 using a forming mold. The overlap of the longitudinal wrapping is achieved by welding or pressing to ensure electrical continuity. The micropores of the microporous copper foil are pre-fabricated by laser drilling or chemical etching, with a pore diameter of 0.1 mm-0.3 mm (preferably 0.15 mm-0.25 mm) and a pore density of 80 pores / cm²-150 pores / cm² to achieve optimal high-frequency absorption.

[0085] Third shielding layer 23 (extrusion): A layer of semi-conductive polyethylene with a nominal thickness of 0.5 mm is continuously extruded onto the outside of the microporous copper foil using an extruder. The volume resistivity of this material is controlled at 10 Ω·cm. 4 Ω.cm-10 6 Within the range of Ω.cm. Extrusion temperature needs to be precisely controlled to avoid damaging the microporous copper foil.

[0086] 7. Construction of the self-monitoring layer

[0087] Outside the semi-conductive polyethylene layer (third shielding layer 23), water-blocking yarn is wrapped around it, and two inductive monitoring lines 31 are placed symmetrically and parallel to each other along the cable axis. The inductive monitoring lines 31 are made of metallized conductive fiber bundles with a nominal diameter of 0.5mm-0.8mm, and are tightly bonded to the surface of the third shielding layer 23 to form a stable electrical contact. The inductive monitoring lines 31 are communicatively connected to an online monitoring unit, used to monitor changes in the insulation state between the third shielding layer 23 and the cable core 1 and to locate fault points using the time-domain reflectometry principle.

[0088] 8. Inner lining layer 5 and pressure-resistant armor layer 6

[0089] Inner liner 5: A thin polyethylene inner liner is extruded over the woven water-resistant yarn as a waterproof buffer layer.

[0090] Compression armor layer 6: It adopts double-layer galvanized steel strip with gap wrapping method for armoring, with a gap ratio of ≤50% and a steel strip thickness of 0.32mm, so as to improve the compression and tensile mechanical strength of the cable.

[0091] 9. Outer sheath 7 extruded

[0092] Finally, an environmentally friendly black linear low-density polyethylene outer sheath with a nominal thickness of 1.9 mm is extruded using an extruder. The extrusion temperature, traction speed, and cooling water tank are coordinated to ensure that the sheath surface is smooth, the thickness is uniform (eccentricity ≤15%), and there are no bubbles or impurities.

[0093] 10. Finished Product Inspection

[0094] The finished cables undergo comprehensive performance testing, including conductor DC resistance, insulation resistance, dielectric strength, working capacitance, characteristic impedance, crosstalk attenuation, shielding effectiveness, and simulated fault monitoring, to ensure that the products meet design requirements.

[0095] Example 2

[0096] Based on Example 1, this embodiment makes adaptive adjustments to the outer sheath 7 material for cables that need to be laid in areas with high requirements for termite damage, flame retardancy, cold resistance, or rodent prevention. All other structures (including conductor 10, insulation, composite shielding layer 2, self-monitoring layer, and armor layer) and manufacturing processes are the same as in Example 1.

[0097] Termite-resistant type: An environmentally friendly termite repellent is added to the outer sheath 7 polyethylene material. The termite repellent is an organophosphate or pyrethroid compound, and the addition amount is 2%-5% (determined according to efficacy and environmental protection requirements).

[0098] Flame-retardant type: The outer sheath 7 material is made of environmentally friendly low-smoke halogen-free flame-retardant polyolefin with an oxygen index >36. When burning, it produces low smoke, low toxicity, and no dripping. The smoke density and toxicity release meet the relevant standards for railway cables.

[0099] Cold-resistant type: The outer sheath 7 material is made of cold-resistant polyethylene or cold-resistant low-smoke halogen-free flame-retardant polyolefin, which can be used stably for a long time in ultra-low temperature environment of -40℃ without cracking or becoming brittle, meeting the laying requirements of high-altitude and cold regions.

[0100] Rodent-proof type: The outer sheath material is made of environmentally friendly rodent repellent and polyethylene, which has excellent rodent-proof performance, high mechanical strength, aging resistance, non-toxic and environmentally friendly, and is suitable for sections of railway lines with high rodent-proof requirements.

[0101] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0102] Finally, it should be noted that this invention is not limited to the optional embodiments described above, and anyone can derive other various forms of products under the guidance of this invention. The specific embodiments described above should not be construed as limiting the scope of protection of this invention, which should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A railway digital signal cable with self-monitoring function, characterized in that, Railway digital signal cables consist of a cable core, a composite shielding layer, and a self-monitoring layer, arranged sequentially from the inside out. The composite shielding layer covers the outside of the cable core and includes a first shielding layer, a second shielding layer, and a third shielding layer arranged sequentially from the inside out. The first shielding layer is a metal-plastic composite tape wrapping layer used to reflect low-frequency electromagnetic interference. The second shielding layer is a metal foil layer with a microporous structure, which is configured to generate resonance in a predetermined high-frequency band to absorb high-frequency electromagnetic interference energy. The third shielding layer is a semi-conductive polymer layer or a semi-conductive composite material layer used to smooth the residual electric field and provide an equipotential reference surface. The self-monitoring layer includes at least two inductive monitoring lines arranged along the cable axis outside the third shielding layer. The inductive monitoring lines and the third shielding layer form a distributed parameter sensor. The inductive monitoring lines are communicatively connected to an online monitoring unit, which monitors the insulation state changes between the third shielding layer and the cable core through the time domain reflection principle, and locates the fault point.

2. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The microporous structure parameters of the second shielding layer are: pore diameter 0.1mm-0.3mm, pore density 50 pores / cm³. 2 -200 pieces / cm 2 The microporous structure is formed by chemical etching, laser drilling or mechanical perforation.

3. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The second shielding layer is made of microporous copper foil or microporous nickel foil, which is wrapped around the outside of the first shielding layer in a longitudinal wrapping manner, and the longitudinal wrapping overlap is electrically continuous by welding or pressing.

4. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The volume resistivity of the third shielding layer is 10. 4 Ω.cm-10 6 The third shielding layer is Ω.cm thick and 0.3mm-0.8mm thick. The third shielding layer is tightly bonded to the second shielding layer by hot pressing or extrusion.

5. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The number of inductive monitoring lines is two, and the two inductive monitoring lines are arranged symmetrically and parallel to each other along the cable axis. The inductive monitoring lines are selected from metallized conductive fiber bundles, flexible copper braided tapes or tinned copper stranded wires, and the diameter is 0.5mm-0.8mm.

6. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The self-monitoring layer also includes a water-blocking yarn layer woven or wrapped around the outside of the sensing monitoring line, the water-blocking yarn layer being used to press the sensing monitoring line tightly against the surface of the third shielding layer.

7. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The cable core includes multiple shielded four-wire groups and multiple unshielded four-wire groups. Each wire group is twisted together at a predetermined pitch. The cable core is wrapped with at least one layer of polyester tape, and the overlap rate of the polyester tape is ≥15%.

8. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The first shielding layer is a single-sided self-adhesive aluminum-plastic composite tape with a thickness of 0.06mm-0.08mm and a wrapping overlap rate of ≥25%; two soft copper drain lines are placed inside the first shielding layer.

9. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The insulated single wire in the cable core has a three-layer co-extruded structure of sheath-foam-sheath, including an inner sheath, a foam layer and an outer sheath layer that are sequentially wrapped around the outside of the conductor, and a high dielectric constant ceramic film is coated on the surface of the outer sheath layer. The high dielectric constant ceramic film is a barium titanate ceramic film with a thickness of 5μm-10μm and a thickness deviation of <±0.5μm. The barium titanate ceramic film is formed by precision coating, thermal curing or ultraviolet curing process, and its dielectric constant fluctuation rate in the 1MHz-10GHz frequency band is ≤3%.

10. The railway digital signal cable with self-monitoring function according to claim 1, characterized in that, The railway digital signal cable also includes an inner lining layer, a pressure-resistant armor layer, and an outer sheath arranged sequentially from the inside to the outside of the self-monitoring layer; the pressure-resistant armor layer is a double-layer galvanized steel strip with a gap wrapping structure and a gap ratio of ≤50%; the outer sheath is made of environmentally friendly linear low-density polyethylene or low-smoke halogen-free flame-retardant polyolefin.

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