Optical fiber temperature measurement and semi-conductive buffer layer early warning water-blocking medium voltage cable and test method

Abstract

The present application relates to the technical field of power cable, in particular to a water-blocking medium-voltage cable with optical fiber temperature measurement and semi-conductive buffer layer early warning and a testing method. The water-blocking medium-voltage cable is composed of a conductor structure, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a metal shielding layer, a filling layer, a distributed optical fiber sensing composite water-blocking layer, an inner liner, a metal sheath and an outer sheath. The distributed sensing optical fiber composite water-blocking layer is composed of an inner layer semi-conductive water-blocking tape, an outer layer insulation water-blocking tape and a distributed sensing optical fiber sandwiched between the two layers of water-blocking tapes, and the distributed sensing optical fiber is arranged in an S shape or a spiral manner. Micro-strain is generated by the water-blocking tape swelling when encountering water, combined with temperature-strain dual-parameter distributed monitoring, to realize micro-water ingress, damp and overheating condition identification, eliminate environmental temperature interference, realize early warning and accurate positioning of the cable, the semi-conductive buffer layer has the functions of voltage equalization, buffering and water blocking, and improves the reliability and operation safety of long-term online monitoring of the medium-voltage cable.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, and in particular to a water-blocking medium-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning, and a testing method thereof. Background Technology

[0002] Medium-voltage power cables are crucial transmission equipment in urban power distribution networks, industrial parks, municipal infrastructure, rail transit, and new energy power distribution systems, undertaking the task of safely and stably transmitting medium-voltage electrical energy. To improve the operational reliability of cables in underground direct burial, cable trenches, integrated pipe corridors, and humid environments, existing medium-voltage cables typically have water-blocking tape, water-blocking yarn, or water-blocking filler materials installed outside the insulation layer to form a longitudinal or radial water-blocking structure, slowing down the diffusion of external moisture into the cable interior. When the outer sheath is subjected to mechanical damage, joint seal failure, long-term immersion in water, or damage from construction forces, external moisture may still gradually seep into the cable interior along the tiny gaps between the shielding layer, filler layer, and insulation layer. With continuous moisture intrusion, the XLPE insulation layer is prone to water treeing aging, leading to a decrease in dielectric properties, increased partial discharge, and reduced insulation strength, which may ultimately cause insulation breakdown, line tripping, or even large-scale power outages. Therefore, early moisture monitoring and fault warning for water-blocking medium-voltage cables are of great significance for ensuring the long-term safe and stable operation of power distribution systems.

[0003] However, existing water-blocking low-voltage cables still primarily rely on passive protection through water-blocking materials, lacking real-time sensing capabilities for the state after moisture intrusion. The health status of the cable is typically assessed through insulation resistance testing, partial discharge detection, or periodic inspections. Conventional insulation testing can only detect anomalies after significant insulation degradation, when insulation performance has noticeably declined or water treeing has progressed to a certain extent. By this time, water treeing is irreversible, making it impossible to promptly identify trace amounts of water ingress for early fault prediction, resulting in monitoring lag. Secondly, existing external fiber optic temperature sensors or conventional online monitoring devices have low coupling with the cable body, making it difficult to directly sense the minute changes in the water-blocking structure caused by water absorption and expansion. Furthermore, they are easily affected by factors such as ambient temperature, seasonal changes, and laying conditions, making it difficult to accurately distinguish between different operating conditions such as overload heating, ambient temperature rise, and moisture ingress, leading to false alarms. In addition, external optical fibers are susceptible to problems such as surface temperature, temperature difference in the laying environment, mechanical damage, corrosion and construction damage. They are difficult to distinguish between heat generated by defects in the fiber itself and environmental fluctuations, cannot be deeply coupled with the water-blocking structure, cannot detect early trace moisture infiltration, have a high false alarm rate, and cannot meet the needs of long-term online monitoring, becoming a technical pain point for the safe operation of medium-voltage water-blocking cables. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a water-blocking low-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning, as well as a testing method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a water-blocking submersible cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning. The water-blocking submersible cable includes a first cable structure, which comprises a conductor structure, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a metallic shielding layer, a filler layer, and wrapping tape. The conductor structure uses multiple conventional copper single wires twisted together to form a single conductor, which is used to carry medium-voltage current and reduce resistance loss during power transmission. It is used to transmit and distribute medium-voltage power. The copper wire has high conductivity, strong current carrying capacity and low conductive loss. The conductor structure is provided with a conductor shielding layer to eliminate the electric field concentration effect on the surface of the conductor structure, so that a uniform and continuous radial electric field distribution is formed between the conductor structure and the XLPE insulation layer. The XLPE insulation layer is wrapped around the conductor shielding layer and serves as the main electrical insulation structure of the water-blocking low-voltage cable. It is used to isolate the high-potential conductor from the external grounding structure and prevent current leakage and breakdown. An insulating shielding layer is provided on the outside of the XLPE insulation layer. This insulating shielding layer is used to homogenize the external electric field of the XLPE insulation layer and keep the outer surface of the XLPE insulation layer at the same potential. The insulating shielding layer is surrounded by a metal shielding layer, and the insulating shielding layer also provides a stable electrical transition interface for the metal shielding layer. The three conductors are twisted together, and a layer of cushioning and pressure-resistant wrapping tape is wrapped tightly around the outer shielding part of the metal shielding layer, so that the cable is round and the gaps and voids between the metal shielding layer and the wrapping tape are pre-filled with an appropriate amount of water-blocking material to form a filling layer.

[0006] Furthermore, in a preferred embodiment of the present invention, the water-blocking material includes water-blocking yarn, water-blocking tape, petroleum jelly, and water-blocking paste.

[0007] Furthermore, in a preferred embodiment of the present invention, a second cable structure is provided outside the first cable structure, the second cable structure including a distributed optical fiber sensing composite water-blocking layer, an inner lining layer, a metal sheath, and an outer sheath; wherein, the distributed optical fiber sensing composite water-blocking layer is composed of three layers: an inner semi-conductive water-blocking tape, a distributed sensing optical fiber, and an outer insulating water-blocking tape.

[0008] Furthermore, in a preferred embodiment of the present invention, the inner semiconducting resistive water tape is tightly wrapped around the wrapping tape of the first cable structure, the outer insulating water-blocking tape is disposed outside the inner semiconducting resistive water tape, the distributed sensing optical fiber is tightly clamped between the inner semiconducting resistive water tape and the outer insulating water-blocking tape, and the distributed sensing optical fiber is connected to a distributed optical fiber strain-temperature demodulator.

[0009] Furthermore, in a preferred embodiment of the present invention, the distributed sensing optical fiber is laid in an axial S-shaped reciprocating layout between two layers of water-blocking tape, and is assembled into a whole by a hot-press curing process, and then wrapped around the outside of the wrapping tape by a wrapping process.

[0010] Furthermore, in a preferred embodiment of the present invention, the outer insulating water-blocking tape is extruded with an inner lining layer, the inner lining layer is longitudinally wrapped with a metal sheath, and the outermost layer of the metal sheath is extruded with an outer sheath made of polyethylene or polyvinyl chloride.

[0011] Furthermore, in a preferred embodiment of the present invention, the metal sheath is formed by welding aluminum strips together using argon arc welding.

[0012] The second aspect of this invention provides a test method for a water-blocking medium-voltage cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning, applicable to any of the fiber optic temperature measurement and semi-conductive buffer layer for early warning of water blockage, specifically including the following steps: By deploying and connecting the water-blocking medium-voltage cable in the target power scenario area to perform power transmission operation tests, and simultaneously connecting the distributed sensing optical cable port led out from the end of the water-blocking medium-voltage cable to the fiber optic strain-temperature demodulator for real-time monitoring; Obtain the original design drawings of the water-blocking medium-voltage cable, and use finite element software to model and analyze the cable design parameters in the original design drawings to construct a finite element simulation model of the water-blocking medium-voltage cable. The system acquires several real-time thermal and humidity environmental parameters of the target power scene area within the current time period and multi-source thermal and humidity environmental parameters collected and recorded within a preset historical time period by using the multi-source thermal and humidity environmental parameters and their state data. Based on the theory of air diffusion dynamics, the system performs spatial modeling and dynamic coordinate rendering of the coupled diffusion and propagation of the thermal and humidity environment in the area, thereby generating a priori thermal and humidity environment simulation field of the target power scene area. Based on big data acquisition, a dynamic environmental factor prediction model pre-trained based on air diffusion dynamics theory is obtained. Real-time thermal and humidity environmental parameters and prior thermal and humidity environmental simulation fields are input into the dynamic environmental factor prediction model for prediction. This results in one or more areas prone to thermal and humidity effects that may be subject to abnormal environmental disturbances during the power transmission operation test of the water-blocking low-voltage cable in the target power scenario area. Based on the cable maintenance log, the distribution map of hot spots of heat and moisture infiltration events in the metal sheath of the water-blocking low voltage cable within a preset historical period is extracted. The sub-hot spot distribution corresponding to the early warning error in each area prone to heat and moisture effect is extracted from the hot spot distribution map of heat and moisture infiltration, and defined as the first heat and moisture early warning anchor point map. The temperature distribution-Brillouin frequency shift strain of the damaged water ingress during the testing of the water-resistant medium-voltage cable was analyzed using a fiber optic strain-temperature demodulator. The actual early warning distribution was observed by a finite element simulation model and defined as the second thermal humidity early warning anchor point map. By registering the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps, a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable is conducted based on the positioning registration rate, generating the first test report result. Then, based on the early warning response effectiveness index of strain-temperature dual attributes during testing, the test performance of the qualified test specimen is further analyzed to generate the second test report result.

[0013] Furthermore, in a preferred embodiment of the present invention, the step of obtaining the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps through registration, performing a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable based on the positioning registration rate, generating a first test report result, and further analyzing the test performance of the qualified test specimen based on the early warning response effectiveness index of strain-temperature dual attributes during testing, generating a second test report result, specifically includes the following steps: The first and second thermal humidity warning anchor point maps are superimposed and registered. The positioning registration rate between the thermal humidity warning anchor points is calculated. If there are at least two or more thermal humidity warning anchor points corresponding to the positioning deviation rate during the test, the calibrated water-resistant medium-voltage cable is a non-conforming test product, and the first test report result is generated. If there is at most one or less positioning deviation rate corresponding to the heat and humidity warning anchor point during the test, the calibrated water-blocking medium-voltage cable is a qualified test product. At this time, the strain-temperature dual attribute curve of the water-blocking medium-voltage cable in time to block water and temperature change is obtained by the fiber optic strain-temperature demodulator. Based on the strain-temperature dual-attribute curve, the actual early warning response rate and its corresponding actual response rate when the early warning of the thermal humidity warning anchor point of the water-resistant medium-voltage cable appears are extracted. Based on the target test requirements, the expected early warning response rate and ideal response rate of the ideal temperature measurement compliance of the water-resistant medium-voltage cable product are extracted. If the actual early warning response rate is higher than the expected early warning response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is designated as a superior test product, and a first-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate but the actual response rate is higher than the ideal response rate, or if the actual early warning response rate is higher than the expected early warning response rate but the actual response rate is lower than the ideal response rate, then the water-resistant medium-voltage cable of the quasi-qualified test item is calibrated as a medium-grade test item, and the second-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is classified as an inferior test product, and three categories of test items are obtained. A test report for the water-resistant medium-voltage cable is generated by combining the first, second, and third test item indicators, and a second test report result is produced.

[0014] Furthermore, in a preferred embodiment of the present invention, the step of performing temperature distribution-Brillouin frequency shift strain early warning analysis on the hot water ingress during the testing of a water-resistant medium-voltage cable using an optical fiber strain-temperature demodulator specifically includes the following steps: Through continuous acquisition by the fiber optic strain-temperature demodulator, the strain and temperature values ​​of the composite water-blocking layer based on the distributed sensing optical cable and the distributed sensing optical cable detection of the entire line of the water-blocking medium-voltage cable were obtained in real time during the test. When the strain value exceeds the preset strain threshold but the temperature value is less than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water infiltration and water ingress due to sheath damage, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point. If only the temperature value rises above the preset temperature threshold while the strain value is below the preset strain threshold, then the water-blocking medium-voltage cable is determined to be overloaded and overheated, thus eliminating the false alarm of water ingress from the demodulator. When the strain value exceeds the preset strain threshold and the temperature value is simultaneously greater than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water intrusion, water ingress due to sheath damage, and overload and overheating of the cable core, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point.

[0015] The beneficial technical effects of this invention are as follows: This invention integrates distributed sensing optical fibers into a composite water-blocking layer, forming an integrated composite structure with semiconducting water-blocking tape and insulating water-blocking tape. Without altering the original electrical, mechanical properties, or manufacturing process of the medium-voltage cable, it achieves a seamless integration of multiple functions, including water blocking and sealing, uniform electric field, mechanical buffering, and online monitoring. When external moisture intrudes, the water-blocking tape rapidly absorbs water and expands to seal the seepage channels, simultaneously generating micro-strain signals that can be sensed by the distributed optical fibers. This allows the system to detect minute amounts of water ingress before significant water treeing or insulation degradation occurs in the insulation layer, shifting from traditional post-fault detection to pre-fault warning. Simultaneously, the distributed optical fibers continuously monitor temperature and strain information along the entire cable length. Combined with dual-parameter fusion analysis, this effectively eliminates interference caused by environmental temperature changes and load fluctuations, accurately distinguishing between different operating conditions such as room temperature water ingress, hot water intrusion, and overload heating. This significantly reduces false alarm rates, improves fault identification accuracy, and enables precise location of damp points and abnormal heating points, providing a reliable basis for operation and maintenance. Attached Figure Description

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

[0017] Figure 1 This is a three-dimensional structural diagram of the present invention; Figure 2 This is a cross-sectional planar structural diagram of the present invention; Figure 3 A schematic diagram of the internal unfolded structure of the distributed sensing fiber composite water-blocking layer; Figure 4 This is a schematic diagram illustrating the working and testing principles of the present invention when connected to a demodulator.

[0018] The annotations in the attached figures are explained as follows: 1. Conductor structure; 2. Conductor shielding layer; 3. XLPE insulation layer; 4. Insulating shielding layer; 5. Metallic shielding layer; 6. Filling layer; 7. Wrapping tape; 8. Distributed optical fiber sensing composite water-blocking layer; 8a. Inner semi-conductive water-blocking tape; 8b. Distributed sensing optical fiber; 8c. Outer insulating water-blocking tape; 9. Inner lining layer; 10. Metallic sheath; 11. Outer sheath. Detailed Implementation

[0019] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner. Therefore, they only show the components related to the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0020] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application 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, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., 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. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0023] like Figures 1-4 As shown, the first aspect of the present invention provides a water-blocking sub-high voltage cable with optical fiber temperature measurement and semi-conductive buffer layer early warning. The water-blocking sub-high voltage cable includes a first cable structure, which includes a conductor structure 1, a conductor shielding layer 2, an XLPE insulation layer 3, an insulation shielding layer 4, a metal shielding layer 5, a filling layer 6, and a wrapping tape 7.

[0024] The conductor structure 1 is formed by stranding multiple conventional copper single wires into a single conductor, which is used to carry medium-voltage current and reduce resistance loss during power transmission. It is used to transmit and distribute medium-voltage power. The copper wire has high conductivity, strong current carrying capacity and low conductivity loss. The conductor structure 1 is provided with a conductor shielding layer 2 to eliminate the electric field concentration effect on the surface of the conductor structure 1, so that a uniform and continuous radial electric field distribution is formed between the conductor structure 1 and the XLPE insulation layer 3.

[0025] The XLPE insulation layer 3 is wrapped around the conductor shielding layer 2 and serves as the main electrical insulation structure for blocking the water-cooled low-voltage cable. It is used to isolate the high-potential conductor from the external grounding structure and prevent current leakage and breakdown. An insulating shielding layer 4 is provided on the outside of the XLPE insulation layer 3. The insulating shielding layer 4 is used to homogenize the external electric field of the XLPE insulation layer 3 and keep the outer surface of the XLPE insulation layer 3 at the same potential.

[0026] It should be noted that the XLPE insulation layer 3 utilizes the excellent dielectric properties, high insulation strength, heat aging resistance, and water tree aging resistance of cross-linked polyethylene material to form a reliable electrical isolation layer between the conductor structure 1 and the external metal shielding structure. This effectively withstands the electric field stress generated during medium-voltage operation, preventing leakage, flashover, and insulation breakdown, thus improving the safety and stability of the cable during long-term power transmission. The insulation shielding layer 4 forms a continuous and stable interface with the outer metal shielding layer 5, the water-blocking layer, and the sheath structure 1. While ensuring a uniform electric field distribution, it reduces local potential changes and dielectric polarization effects caused by moisture intrusion, slows down the performance degradation of the insulation layer after moisture absorption, and allows the water-blocking structure to more effectively inhibit the longitudinal and radial diffusion of moisture along the cable, significantly improving the water-blocking performance, water tree aging resistance, and service life of the medium-voltage cable. In addition, the uniform and stable electric field environment also helps the distributed fiber optic sensing system accurately sense temperature changes and local abnormal heating during cable operation, reduces the interference of electric field distortion on monitoring results, and improves the accuracy of online status monitoring and fault early warning for medium-voltage cables with water blocking properties.

[0027] The insulating shielding layer 4 surrounds the metal shielding layer 5, and the insulating shielding layer 4 also provides a stable electrical transition interface for the metal shielding layer 5.

[0028] The three conductors are twisted together, and a layer of cushioning and pressure-resistant wrapping tape 7 is wrapped tightly around the outer shielding part of the metal shielding layer 5, so that the cable is round and the gaps and voids between the metal shielding layer 5 and the wrapping tape 7 are pre-filled with an appropriate amount of water-blocking material to form a filling layer 6.

[0029] It should be noted that the aforementioned electrical transition interface is used to smoothly transition the equipotential state of the outer surface of the insulation shielding layer 4 to the metal grounding shielding structure, promptly dissipating the capacitive current, induced current, and fault short-circuit current generated during operation, effectively suppressing the impact of external electromagnetic interference on the cable transmission performance and distributed optical fiber monitoring signals. Simultaneously, it reduces the coupling of external electromagnetic fields into the cable core, improving the electromagnetic compatibility performance and operational safety of the medium-voltage cable. The wrapping tape 7 forms a stable constraint support structure between the conductor cores, effectively absorbing the squeezing, impact, and vibration loads generated during transportation, laying, and long-term operation. When external moisture enters the cable due to sheath damage or end dampness, the water-blocking material in the filling layer 6 can quickly absorb water, expand, and seal the gaps, cutting off the longitudinal penetration path of moisture along the cable core stranding gaps and interlayer interfaces, preventing further diffusion of moisture to the insulation layer and conductor area, significantly improving the longitudinal water-blocking capacity and moisture-proof sealing performance of the medium-voltage cable.

[0030] In summary, the wrapping tape 7 and the filling layer 6 form a composite structure that combines flexible support and water-blocking sealing. While ensuring the mechanical strength and structural stability of the cable, it further reduces the new voids caused by mechanical deformation during long-term operation, improves the continuous sealing effect of the water-blocking material, and extends the safe operating life of the water-blocking medium-voltage cable in underground, cable trench, tunnel and humid environments. It also provides a uniform and stable covering foundation for the subsequent distributed optical fiber sensing composite water-blocking layer, and improves the reliability and overall service performance of the online monitoring of this water-blocking medium-voltage cable.

[0031] Furthermore, in a preferred embodiment of the present invention, the water-blocking material includes water-blocking yarn, water-blocking tape, petroleum jelly, and water-blocking paste.

[0032] Furthermore, in a preferred embodiment of the present invention, a second cable structure is provided outside the first cable structure, the second cable structure including a distributed optical fiber sensing composite water-blocking layer 8, an inner lining layer 9, a metal sheath 10, and an outer sheath 11; wherein, the distributed optical fiber sensing composite water-blocking layer 8 is composed of three layers: an inner semi-conductive water-blocking tape 8a, a distributed sensing optical fiber 8b, and an outer insulating water-blocking tape 8c.

[0033] It should be noted that the inner semiconducting water-resistant tape 8a combines the functions of semiconducting buffer, electric field equalization, longitudinal water blocking, and fiber bonding force transmission. Both the inner and outer water-resistant tapes contain highly water-swellable resin, which expands rapidly after water intrusion, applying controllable micro-strain to the clamped sensing optical cable. The distributed sensing optical fiber 8b uses tightly packed single-mode sensing optical fiber, adapted to BOTDA / OFDR distributed demodulation technology, and can simultaneously acquire temperature and micro-strain signals.

[0034] Furthermore, in a preferred embodiment of the present invention, the inner semiconducting resistive water tape 8a is tightly wrapped around the wrapping tape of the first cable structure, the outer insulating water-blocking tape 8c is disposed outside the inner semiconducting resistive water tape 8a, the distributed sensing optical fiber 8b is tightly clamped between the inner semiconducting resistive water tape 8a and the outer insulating water-blocking tape 8c, and the distributed sensing optical fiber 8b is connected to a distributed optical fiber strain-temperature demodulator.

[0035] It should be noted that both the inner semi-conductive water-blocking tape 8a and the outer insulating water-blocking tape 8c contain water-swellable materials. When moisture penetrates, the expanding water-blocking tape can apply controllable micro-strain to the distributed sensing optical cable. The outer insulating water-blocking tape 8c and the inner semi-conductive water-blocking tape 8a together form a double-layer composite water-blocking structure. Utilizing the excellent electrical insulation properties and water absorption and expansion characteristics of the insulating water-blocking materials, while ensuring the electrical isolation of the outer layer, when external moisture penetrates, the two water-blocking tapes can absorb water and expand from the inner and outer sides respectively, sealing the gaps between the layers and the seepage channels. This effectively inhibits the longitudinal and radial diffusion of moisture along the cable, improving the waterproof sealing capability and water tree aging resistance of the water-blocking medium-voltage cable in long-term humid environments. The distributed sensing fiber 8b is tightly clamped between the inner semiconducting water-blocking strip 8a and the outer insulating water-blocking strip 8b, placing the fiber in a relatively stable intermediate region where both mechanical protection and heat transfer conditions are relatively stable. On the one hand, this avoids the fiber being directly subjected to compression, friction, and external mechanical impact from the metal structure, improving the long-term operational reliability of the fiber. On the other hand, it can more realistically sense the internal temperature changes, thermal stress distribution, and stress state of the cable, realizing continuous temperature and strain information acquisition along the entire length of the cable.

[0036] Furthermore, in a preferred embodiment of the present invention, the distributed sensing optical fiber is laid in an axial S-shaped reciprocating layout between two layers of water-blocking tape, and is assembled into a whole by a hot-press curing process, and then wrapped around the outside of the wrapping tape by a wrapping process.

[0037] It should be noted that by continuously laying the distributed sensing fiber 8b along the water-blocking medium-voltage cable in an S-shaped reciprocating pattern along the cable axis, a flexible corrugated structure with a certain margin is formed in the cable length direction. Compared with the straight laying method, on the one hand, the S-shaped reciprocating layout can provide sufficient space for the fiber to compensate for expansion and contraction. When the cable is subjected to bending, stretching, torsion, and thermal expansion and contraction during transportation, laying, and long-term operation, the fiber can absorb axial deformation through the expansion and contraction of the S-curve, reducing local tensile stress concentration and avoiding fiber breakage, micro-bending loss, or signal attenuation due to excessive stress, thus improving the long-term stability and service life of the distributed sensing fiber. On the other hand, the S-shaped laying pattern forms a more uniform contact interface between the fiber and the two layers of water-blocking tape, improving the efficiency of temperature conduction and strain transfer. This allows the fiber to more sensitively and accurately sense subtle changes in the temperature and stress fields along the cable, improving the identification accuracy of abnormal conditions such as local overheating, moisture ingress, and mechanical damage. When external moisture intrudes into the cable, the inner and outer water-blocking strips can quickly absorb water, expand, and block the seepage channels. Meanwhile, the S-shaped distributed sensing optical fibers can simultaneously monitor local temperature changes, changes in thermal conductivity, and strain anomalies caused by moisture intrusion, and transmit the monitoring information to the distributed optical fiber strain-temperature demodulator in real time, realizing the synchronous and coordinated operation of water blocking and online monitoring.

[0038] Furthermore, in a preferred embodiment of the present invention, the outer insulating water-blocking tape 8c is extruded with an inner liner 9, the inner liner 9 is longitudinally wrapped with a metal sheath 10, and the outermost layer of the metal sheath 10 is extruded with an outer sheath 11 made of polyethylene or polyvinyl chloride.

[0039] Furthermore, in a preferred embodiment of the present invention, the metal sheath 10 is formed by welding aluminum strip with argon arc welding.

[0040] It should be noted that the inner lining layer 9 can fill the minor unevenness and interlayer gaps on the outer surface of the distributed sensing fiber composite water-blocking layer 8, improving the overall roundness of the water-blocking medium-voltage cable structure and forming a continuous and uniform covering base for the metal sheath 10, reducing the adverse effects of interlayer gaps on water penetration and mechanical fatigue. The metal sheath 10 is formed by using aluminum strip combined with argon arc welding to form a continuous and closed cable protective shell. The aluminum strip combines metal barrier properties with flexibility. After the argon arc welding seam is fused, it forms an annular sealing layer without obvious gaps, which can effectively prevent groundwater, moisture and corrosive media from penetrating into the cable, significantly improving the radial water-blocking capacity and airtightness of the cable.

[0041] In addition, the continuous and dense metal sheath 10 can serve as a reliable metal shielding barrier to effectively shield against external electromagnetic interference and provide a low-impedance discharge path for fault current and induced current, thereby reducing the impact of the external electromagnetic environment on the distributed optical fiber sensing system and medium-voltage power transmission system and improving the electromagnetic compatibility performance and electrical safety of the cable during operation.

[0042] In summary, the distributed sensing fiber optic port 8b, led out from the end of the water-blocking medium-voltage cable of this invention, is connected to a distributed fiber optic strain-temperature demodulator, which is connected to the background monitoring host. When the cable is in normal operation, the two layers of water-blocking tape maintain their original dimensions. The distributed sensing fiber optic port 8b mainly reflects the normal temperature rise and environmental changes caused by the conductor load, and the strain signal remains within a stable range. The distributed fiber optic strain-temperature demodulator continuously receives the scattered signal transmitted back from the fiber optic cable, and collects the temperature distribution and strain data corresponding to the Brillouin frequency shift along the entire cable in real time, performing real-time demodulation of the temperature and strain distribution along the entire line. When the outer sheath 11 is partially damaged, the joint seal fails, or the underground humid environment causes moisture to begin to penetrate into the cable, moisture enters the distributed sensing fiber optic composite water-blocking layer 8. The water-blocking materials inside the inner semiconducting water-blocking tape 8a and the outer insulating water-blocking tape 8c rapidly absorb moisture and expand in volume. During this expansion, not only are the interlayer gaps and moisture diffusion channels blocked, but the volume change of the water-blocking tape also applies a continuous, uniform, and minute mechanical force to the distributed sensing optical fiber sandwiched within, causing corresponding axial micro-strain in the fiber. The thermal conductivity, dielectric properties, and heat dissipation conditions of the locally damp area change, leading to subtle changes in the temperature distribution at that location. Therefore, the distributed sensing optical fiber 8b can simultaneously acquire both strain anomalies and temperature anomalies. Subsequently, the distributed optical fiber strain-temperature demodulator demodulates the temperature-sensitive and strain-sensitive components in the fiber optic scattered signal, respectively, to obtain the temperature change curve and strain change curve at the corresponding location, achieving joint analysis of the dual attribute parameters of strain and temperature. When the demodulation system detects a sudden increase in local strain with a small temperature change, it determines that the water-blocking strip has absorbed water and expanded, indicating a water ingress in the cable. When the local temperature continues to rise and is accompanied by a synchronous change in strain, it is determined that the damp area has affected the cable's heat dissipation capacity and may develop into insulation dampness or localized overheating faults. If only a temperature change is detected without a corresponding strain change, the system analyzes the changes in ambient temperature and operating load to determine that it is normal load temperature rise or ambient temperature fluctuation, rather than a water ingress fault. When a small amount of water ingress, moisture diffusion, or abnormal overheating is confirmed in a localized area, the system determines the location of the anomaly based on the continuous spatial resolution capability of the distributed sensing fiber optic cable and outputs the corresponding fault location, anomaly level, and development trend to the monitoring terminal, achieving early warning of small amounts of water ingress in the cable, accurate location of damp areas, and intelligent diagnosis of localized overheating faults.

[0043] The second aspect of this invention provides a test method for a water-blocking medium-voltage cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning, applicable to any of the fiber optic temperature measurement and semi-conductive buffer layer for early warning of water blockage, specifically including the following steps: By deploying and connecting the water-blocking medium-voltage cable in the target power scenario area to perform power transmission operation tests, and simultaneously connecting the distributed sensing optical cable port led out from the end of the water-blocking medium-voltage cable to the fiber optic strain-temperature demodulator for real-time monitoring; Obtain the original design drawings of the water-blocking medium-voltage cable, and use finite element software to model and analyze the cable design parameters in the original design drawings to construct a finite element simulation model of the water-blocking medium-voltage cable. The system acquires several real-time thermal and humidity environmental parameters of the target power scene area within the current time period and multi-source thermal and humidity environmental parameters collected and recorded within a preset historical time period by using the multi-source thermal and humidity environmental parameters and their state data. Based on the theory of air diffusion dynamics, the system performs spatial modeling and dynamic coordinate rendering of the coupled diffusion and propagation of the thermal and humidity environment in the area, thereby generating a priori thermal and humidity environment simulation field of the target power scene area. Based on big data acquisition, a dynamic environmental factor prediction model pre-trained based on air diffusion dynamics theory is obtained. Real-time thermal and humidity environmental parameters and prior thermal and humidity environmental simulation fields are input into the dynamic environmental factor prediction model for prediction. This results in one or more areas prone to thermal and humidity effects that may be subject to abnormal environmental disturbances during the power transmission operation test of the water-blocking low-voltage cable in the target power scenario area. Based on the cable maintenance log, the distribution map of hot spots of heat and moisture infiltration events in the metal sheath of the water-blocking low voltage cable within a preset historical period is extracted. The sub-hot spot distribution corresponding to the early warning error in each area prone to heat and moisture effect is extracted from the hot spot distribution map of heat and moisture infiltration, and defined as the first heat and moisture early warning anchor point map. The temperature distribution-Brillouin frequency shift strain of the damaged water ingress during the testing of the water-resistant medium-voltage cable was analyzed using a fiber optic strain-temperature demodulator. The actual early warning distribution was observed by a finite element simulation model and defined as the second thermal humidity early warning anchor point map. By registering the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps, a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable is conducted based on the positioning registration rate, generating the first test report result. Then, based on the early warning response effectiveness index of strain-temperature dual attributes during testing, the test performance of the qualified test specimen is further analyzed to generate the second test report result.

[0044] It should be noted that the multidimensional thermal and humidity environmental parameters include regional temperature, air humidity, wind direction, and wind speed. Due to the limitations and harshness of power transmission operations, some power cables need to be deployed in extreme operating areas or environments with uncontrollable factors, especially in remote tropical areas of South China, hot and humid areas in the middle and lower reaches of the Yangtze River, or tropical rainforests or hot and humid climates in early spring. Under high-load power transmission operations in extreme environments, cables may experience damage to the outer insulation layer and water-blocking layer, failure of joint seals, or damage from external forces during installation, resulting in protective attenuation. The high density of moisture and high heat effect in the surrounding air can seep into the cable from the damaged points, causing insulation breakdown, line tripping, or even large-scale power outages and other power accidents. Although the composite water-blocking layer of the water-blocking medium-voltage cable of this invention can block the penetration of moisture through the micro-strain of the material and the temperature measurement mechanism of distributed optical fiber sensing can lock the heat point of the cable, there may be processing deviations during the production of the water-blocking medium-voltage cable. This may cause the material to fail to exert the ultimate micro-strain constraint barrier performance, or the misalignment of the distributed sensing optical fiber may cause inaccurate high-temperature positioning of the cable's tiny water ingress points. This significantly reduces the power transmission protection efficiency and safety factor of the water-blocking medium-voltage cable of this invention under extreme environments. In response, this method constructs a thermal and humid environment field that closely replicates the local reality of the target power scenario area using prior known multi-dimensional environmental parameters to conduct product performance testing on the water-blocking medium-voltage cable. Under the diffusion probability distribution of the prior thermal and humid environment simulation field, a dynamic environmental factor prediction model following air diffusion dynamics is introduced to predict the regional thermal and humid environment effect in the current season. This allows for the proactive tracking and locking of the latent thermal and humid environment points that can implicitly penetrate the interior of the water-blocking medium-voltage cable and inhibit or damage its power transmission performance, i.e., the areas prone to thermal and humid effects. This achieves a pre-constraint effect on test oscillations and guides the main observation perspective of cable performance testing.

[0045] Furthermore, the hotspots of thermal ingress points in the water-resistant medium-voltage cable during past periods of heat and humidity effects in areas prone to heat and humidity are visualized (first heat and humidity early warning anchor point map). This reveals the dynamic early warning spatial prior of the distribution of failures in the water-resistant medium-voltage cable under harsh heat and humidity environments, providing an interpretable and highly reliable reference baseline for the analysis of early warning positioning accuracy in subsequent cable testing. The first and second heat and humidity early warning anchor point maps are registered. After registration, the early warning anchor points of the two maps are aligned in a limited manner. The alignment rate reflects the spatial early warning positioning accuracy of the water-resistant medium-voltage cable based on the fiber optic strain-temperature demodulator for its own minute moisture points and high-temperature hot spots. This allows for a preliminary analysis of the fault location performance and positioning drift error of the water-resistant medium-voltage cable product. This method utilizes predictive observation constraints based on prior thermal and humid environments to test the accuracy of early warning and location of localized dampness and overheating conditions in medium-voltage cables. This allows for a comprehensive evaluation of the cable's insulation performance, water-blocking performance, mechanical stability, and long-term reliability under complex operating environments such as dampness, immersion, and underground installation. It enables the timely detection and prevention of potential faults. Based on the test results, the material selection, improvement, manufacturing process, and installation and maintenance schemes of medium-voltage cables can be optimized, thereby improving the environmental adaptability and service life of medium-voltage cables, reducing operation and maintenance costs and fault repair frequency, and enhancing the reliable power supply and safe and stable operation capabilities of medium-voltage cables in complex environments.

[0046] In addition, the method of using multi-source thermal and humid environment parameters and their state data to perform spatial modeling and dynamic coordinate rendering of the coupled diffusion propagation of the thermal and humid environment in the region based on the theory of air diffusion dynamics, and generating a priori thermal and humid environment simulation field of the target power scenario area, includes the following steps: The monitoring logs of the environmental sensor array are retrieved to obtain the multi-source thermal and humidity environmental parameters of the target power scene area within a preset time period, and the historical thermal and humidity state vectors corresponding to each multi-source thermal and humidity environmental parameter are extracted. Using aerodynamic knowledge graph retrieval, the coupling diffusion index of different multi-source thermal and humid environmental parameters is obtained when historical thermal and humid state vectors appear in the regional air during a preset time period. Based on the coupling diffusion index, the coupling diffusion strength and diffusion propagation scale of different thermal and humid environmental samples are preset. A Gaussian kernel function algorithm is introduced. Based on the diffusion propagation scale, the Gaussian kernel function algorithm is used to perform propagation dynamics calculations on the historical thermal and humid state vectors corresponding to each multi-source thermal and humid environment parameter by relying on the coupling diffusion joint strength, and a thermal and humid environment diffusion kernel matrix is ​​generated. Using the regional probability matrix of Markov chain as the underlying architecture and combining aerodynamic theory, the diffusion probability of the target power scene region is rasterized and then embedded into the thermal and humid environment diffusion kernel matrix. The jump probability of regional diffusion distribution is calculated, and the spatial diffusion probability transfer framework of thermal and humid environment is output. Obtain the geographic coordinate spatial domain of the target power scenario area, decompose the thermal and humid diffusion features of the spatial diffusion probability transfer framework, and construct a diffusion coordinate sequence through a series of non-trivial feature values; Based on the diffusion coordinate sequence, the multi-source thermal and humid environment parameters are interpolated into the geographic coordinate spatial domain and reconstructed and rendered to finally generate a priori thermal and humid environment simulation field for the target power scene area.

[0047] It should be noted that, due to the implicit nonlinear characteristics of thermal and humid environment diffusion—such as temperature gradient changes caused by local heat sources, humidity diffusion caused by humid air migration, and local environmental disturbances caused by airflow—a coupled diffusion index is used to pre-determine the coupled diffusion strength and diffusion propagation scale of the thermal and humid environment sample in order to accurately capture the environmental state. The coupled diffusion strength represents the degree of synergistic influence between temperature and humidity changes in the thermal and humid environment sample, measuring the significant synergistic migration effect between the temperature and humidity fields. The coupled diffusion strength reflects the synchronicity of temperature and humidity gradients in the air of the target power scenario area, the mutually reinforcing coupling force of heat diffusion and water vapor diffusion, and the consistency of thermal and humid state changes. The diffusion propagation scale characterizes the spatial range or diffusion distance at which changes in the thermal and humid environment state can affect the surrounding area. The diffusion propagation scale reveals the heat propagation distance, water vapor migration range, and spatial continuity of environmental state changes within the regional air. Subsequently, a Gaussian kernel function is used to transform the thermal and humid state distance into diffusion weights. By calculating the environmental similarity between different thermal and humid sampling points, a diffusion kernel matrix describing the thermal and humid state connections is constructed. This establishes a strong correlation mechanism between similar environmental regions, while weakening the diffusion series weights between significantly different local regions, generating a thermal and humid environment diffusion kernel matrix. This matrix effectively captures and elucidates the nonlinear diffusion law of the thermal and humid environment within the target power scene area, improves the diffusion state correlation strength of the thermal and humid environment, and highly renders the realistic humidity and temperature environmental field effects of the target power scene area. However, the thermal and humid environment diffusion kernel matrix only represents the spatial similarity of coupled propagation and cannot visualize the thermal and humid environment state following the random propagation direction of aerodynamics and the migration trend of humidity and temperature in the target power scene area. Therefore, by combining a Markov chain model and aerodynamic theory, the thermal and humid environment state series weights are transformed into a probability transition matrix, so that each thermal and humid environment sampling point has a probability label description of migration to the neighboring state, thereby simulating the diffusion path of the thermal and humid environment state randomly walking in the regional space. The spatial diffusion probability transfer framework enables dynamic diffusion interpretation of static thermal and humid environment similarity analysis, improving the dynamic simulation accuracy of the environmental simulation field for the changes in air humidity, temperature and state in the target store scene area, and providing high-fidelity and realistic environmental effect support for subsequent water-resistant low-voltage cable testing.

[0048] Furthermore, in a preferred embodiment of the present invention, the step of obtaining the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps through registration, performing a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable based on the positioning registration rate, generating a first test report result, and further analyzing the test performance of the qualified test specimen based on the early warning response effectiveness index of strain-temperature dual attributes during testing, generating a second test report result, specifically includes the following steps: The first and second thermal humidity warning anchor point maps are superimposed and registered. The positioning registration rate between the thermal humidity warning anchor points is calculated. If there are at least two or more thermal humidity warning anchor points corresponding to the positioning deviation rate during the test, the calibrated water-resistant medium-voltage cable is a non-conforming test product, and the first test report result is generated. If there is at most one or less positioning deviation rate corresponding to the heat and humidity warning anchor point during the test, the calibrated water-blocking medium-voltage cable is a qualified test product. At this time, the strain-temperature dual attribute curve of the water-blocking medium-voltage cable in time to block water and temperature change is obtained by the fiber optic strain-temperature demodulator. Based on the strain-temperature dual-attribute curve, the actual early warning response rate and its corresponding actual response rate when the early warning of the thermal humidity warning anchor point of the water-resistant medium-voltage cable appears are extracted. Based on the target test requirements, the expected early warning response rate and ideal response rate of the ideal temperature measurement compliance of the water-resistant medium-voltage cable product are extracted. If the actual early warning response rate is higher than the expected early warning response rate and the actual response rate is also greater than the ideal response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is designated as a superior test product, and a first-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate but the actual response rate is higher than the ideal response rate, or if the actual early warning response rate is higher than the expected early warning response rate but the actual response rate is lower than the ideal response rate, then the water-resistant medium-voltage cable of the quasi-qualified test item is calibrated as a medium-grade test item, and the second-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate and the actual response rate is also lower than the ideal response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is calibrated as an inferior test product, and three types of test item indicators are obtained. A test report for the water-resistant medium-voltage cable is generated by combining the first, second, and third test item indicators, and a second test report result is produced.

[0049] It should be noted that if at least two or more positioning deviation rates correspond to thermal and humidity warning anchor points during the test, it indicates that the moisture and overheating warning locations located by the water-blocking medium-voltage cable have a significant spatial deviation compared to the precisely known fault warning locations. This suggests that the water-blocking medium-voltage cable is inaccurate in warning and locating potential hot water ingress fault points under the influence of heat and humidity within the target power scenario area, falling under the unqualified standard for cable deployment, and is therefore calibrated as an unqualified test product. Conversely, a deeper analysis of its test performance is required. If the actual warning response rate is higher than the expected warning response rate and the actual response rate is also greater than the ideal response rate, it indicates that the water-blocking medium-voltage cable, while ensuring the accuracy of hot water ingress fault location, exhibits excellent warning performance in terms of temperature and strain monitoring sensitivity and response timeliness (compared to the threshold boundary), without false alarms, response delays, or warning lag. Therefore, this water-blocking medium-voltage cable product is calibrated as a superior test product. If the actual warning response rate is lower than the expected warning response rate but the actual response rate is higher than the ideal response rate, it indicates that the cable's sensitivity to detecting micro-strain expansion of the water-blocking layer due to moisture and high-temperature overheating is low or delayed, but the timely warning speed for both meets the ideal requirements. Alternatively, if the actual warning response rate is higher than the expected warning response rate but the actual response rate is lower than the ideal response rate, it indicates that the cable's dynamic warning response efficiency to detecting micro-strain expansion of the water-blocking layer due to moisture and high-temperature overheating is high, but the timely warning speed for both is slow. Both test indicators show that the warning response performance of this water-blocking medium-voltage cable is skewed, therefore it is calibrated as a medium-grade test product. If the actual warning response rate is lower than the expected warning response rate and the actual response rate is also lower than the ideal response rate, it indicates that the cable's strain and temperature-based warnings are prone to false alarms of hot water ingress and warning lag, therefore it is calibrated as a poor-grade test product.

[0050] This method enables a multi-dimensional comprehensive evaluation of the accuracy of hot water ingress early warning positioning and the performance of early warning response for water-blocking medium-voltage cables, based on fault characteristics such as micro-strain expansion and abnormal temperature rise caused by moisture in hot and humid environments. This allows for the grading of the operational performance of water-blocking medium-voltage cables, improving the accuracy and reliability of cable fault early warning results. Furthermore, by constructing a grading mechanism for superior, medium, unqualified, and inferior test samples, it achieves quantitative screening and quality traceability of water-blocking medium-voltage cables with different performance levels. This provides reliable data for cable product factory testing, operation and maintenance, and fault prevention, enhancing the safety, reliability, and intelligent operation and maintenance level of medium-voltage cables in power systems.

[0051] Furthermore, in a preferred embodiment of the present invention, the step of performing temperature distribution-Brillouin frequency shift strain early warning analysis on the hot water ingress during the testing of a water-resistant medium-voltage cable using an optical fiber strain-temperature demodulator specifically includes the following steps: Through continuous acquisition by the fiber optic strain-temperature demodulator, the strain and temperature values ​​of the composite water-blocking layer based on the distributed sensing optical cable and the distributed sensing optical cable detection of the entire line of the water-blocking medium-voltage cable were obtained in real time during the test. When the strain value exceeds the preset strain threshold but the temperature value is less than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water infiltration and water ingress due to sheath damage, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point. If only the temperature value rises above the preset temperature threshold while the strain value is below the preset strain threshold, then the water-blocking medium-voltage cable is determined to be overloaded and overheated, thus eliminating the false alarm of water ingress from the demodulator. When the strain value exceeds the preset strain threshold and the temperature value is simultaneously greater than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water intrusion, water ingress due to sheath damage, and overload and overheating of the cable core, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point.

[0052] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A water-blocking sub-high-voltage cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning, the water-blocking sub-high-voltage cable comprising a first cable structure, the first cable structure comprising a conductor structure, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a metallic shielding layer, a filler layer, and wrapping tape, characterized in that: The conductor structure uses multiple conventional copper single wires twisted together to form a single conductor, which is used to carry medium-voltage current and reduce resistance loss during power transmission. It is used to transmit and distribute medium-voltage power. The copper wire has high conductivity, strong current carrying capacity and low conductive loss. The conductor structure is provided with a conductor shielding layer to eliminate the electric field concentration effect on the surface of the conductor structure, so that a uniform and continuous radial electric field distribution is formed between the conductor structure and the XLPE insulation layer. The XLPE insulation layer is wrapped around the conductor shielding layer and serves as the main electrical insulation structure of the water-blocking low-voltage cable. It is used to isolate the high-potential conductor from the external grounding structure and prevent current leakage and breakdown. An insulating shielding layer is provided on the outside of the XLPE insulation layer. This insulating shielding layer is used to homogenize the external electric field of the XLPE insulation layer and keep the outer surface of the XLPE insulation layer at the same potential. The insulating shielding layer is surrounded by a metal shielding layer, and the insulating shielding layer also provides a stable electrical transition interface for the metal shielding layer. The three conductors are twisted together, and a layer of cushioning and pressure-resistant wrapping tape is wrapped tightly around the outer shielding part of the metal shielding layer, so that the cable is round and the gaps and voids between the metal shielding layer and the wrapping tape are pre-filled with an appropriate amount of water-blocking material to form a filling layer.

2. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 1, characterized in that, The water-blocking materials include water-blocking yarn, water-blocking tape, petroleum jelly, and water-blocking paste.

3. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 1, characterized in that, The first cable structure is externally provided with a second cable structure, which includes a distributed optical fiber sensing composite water-blocking layer, an inner lining layer, a metal sheath, and an outer sheath; wherein, the distributed optical fiber sensing composite water-blocking layer is composed of three composite layers: an inner semi-conductive water-blocking tape, a distributed sensing optical fiber, and an outer insulating water-blocking tape.

4. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 3, characterized in that, The inner semiconducting resistive water tape is tightly wrapped around the wrapping tape of the first cable structure, and the outer insulating water-blocking tape is disposed outside the inner semiconducting resistive water tape. The distributed sensing optical fiber is tightly clamped between the inner semiconducting resistive water tape and the outer insulating water-blocking tape, and the distributed sensing optical fiber is connected to the distributed optical fiber strain-temperature demodulator.

5. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 4, characterized in that, The distributed sensing optical fiber is laid in an axial S-shaped reciprocating layout between two layers of water-blocking tape, and is assembled into a whole by a hot-press curing process, and then wrapped around the outside of the wrapping tape by a wrapping process.

6. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 4, characterized in that, The outer insulating water-blocking tape is extruded with an inner lining layer, and the inner lining layer is longitudinally wrapped with a metal sheath. The outermost layer of the metal sheath is extruded with a polyethylene or polyvinyl chloride outer sheath.

7. The water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 1, characterized in that, The metal sheath is formed by welding aluminum strips together using argon arc welding.

8. A test method for a water-resistant medium-voltage cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning, applicable to the water-resistant medium-voltage cable with fiber optic temperature measurement and a semi-conductive buffer layer for early warning as described in any one of claims 1-7, characterized in that, Specifically, the following steps are included: By deploying and connecting the water-blocking medium-voltage cable in the target power scenario area to perform power transmission operation tests, and simultaneously connecting the distributed sensing optical cable port led out from the end of the water-blocking medium-voltage cable to the fiber optic strain-temperature demodulator for real-time monitoring; Obtain the original design drawings of the water-blocking medium-voltage cable, and use finite element software to model and analyze the cable design parameters in the original design drawings to construct a finite element simulation model of the water-blocking medium-voltage cable. The system acquires several real-time thermal and humidity environmental parameters of the target power scene area within the current time period and multi-source thermal and humidity environmental parameters collected and recorded within a preset historical time period by using the multi-source thermal and humidity environmental parameters and their state data. Based on the theory of air diffusion dynamics, the system performs spatial modeling and dynamic coordinate rendering of the coupled diffusion and propagation of the thermal and humidity environment in the area, thereby generating a priori thermal and humidity environment simulation field of the target power scene area. Based on big data acquisition, a dynamic environmental factor prediction model pre-trained based on air diffusion dynamics theory is obtained. Real-time thermal and humidity environmental parameters and prior thermal and humidity environmental simulation fields are input into the dynamic environmental factor prediction model for prediction. This results in one or more areas prone to thermal and humidity effects that may be subject to abnormal environmental disturbances during the power transmission operation test of the water-blocking low-voltage cable in the target power scenario area. Based on the cable maintenance log, the distribution map of hot spots of heat and moisture infiltration events in the metal sheath of the water-blocking low voltage cable within a preset historical period is extracted. The sub-hot spot distribution corresponding to the early warning error in each area prone to heat and moisture effect is extracted from the hot spot distribution map of heat and moisture infiltration, and defined as the first heat and moisture early warning anchor point map. The temperature distribution-Brillouin frequency shift strain of the damaged water ingress during the testing of the water-resistant medium-voltage cable was analyzed using a fiber optic strain-temperature demodulator. The actual early warning distribution was observed by a finite element simulation model and defined as the second thermal humidity early warning anchor point map. By registering the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps, a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable is conducted based on the positioning registration rate, generating the first test report result. Then, based on the early warning response effectiveness index of strain-temperature dual attributes during testing, the test performance of the qualified test specimen is further analyzed to generate the second test report result.

9. The test method for a water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 8, characterized in that, The process involves obtaining the positioning registration rate of different anchor points between the first and second thermal humidity early warning anchor point maps through registration, conducting a preliminary analysis of the unqualified test performance of the water-resistant medium-voltage cable based on the positioning registration rate, generating a first test report result, and further analyzing the test performance of the qualified test specimen based on the early warning response effectiveness index of strain-temperature dual attributes during testing, generating a second test report result. This process specifically includes the following steps: The first and second thermal humidity warning anchor point maps are superimposed and registered. The positioning registration rate between the thermal humidity warning anchor points is calculated. If there are at least two or more thermal humidity warning anchor points corresponding to the positioning deviation rate during the test, the calibrated water-resistant medium-voltage cable is a non-conforming test product, and the first test report result is generated. If there is at most one or less positioning deviation rate corresponding to the heat and humidity warning anchor point during the test, the calibrated water-blocking medium-voltage cable is a qualified test product. At this time, the strain-temperature dual attribute curve of the water-blocking medium-voltage cable in time to block water and temperature change is obtained by the fiber optic strain-temperature demodulator. Based on the strain-temperature dual-attribute curve, the actual early warning response rate and its corresponding actual response rate when the early warning of the thermal humidity warning anchor point of the water-resistant medium-voltage cable appears are extracted. Based on the target test requirements, the expected early warning response rate and ideal response rate of the ideal temperature measurement compliance of the water-resistant medium-voltage cable product are extracted. If the actual early warning response rate is higher than the expected early warning response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is designated as a superior test product, and a first-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate but the actual response rate is higher than the ideal response rate, or if the actual early warning response rate is higher than the expected early warning response rate but the actual response rate is lower than the ideal response rate, then the water-resistant medium-voltage cable of the quasi-qualified test item is calibrated as a medium-grade test item, and the second-class test item index is obtained. If the actual early warning response rate is lower than the expected early warning response rate, then the water-resistant medium-voltage cable of the quasi-qualified test product is classified as an inferior test product, and three categories of test items are obtained. A test report for the water-resistant medium-voltage cable is generated by combining the first, second, and third test item indicators, and a second test report result is produced.

10. The test method for a water-resistant high-voltage cable with fiber optic temperature measurement and semi-conductive buffer layer early warning according to claim 8, characterized in that, The method of performing temperature distribution-Brillouin frequency shift strain early warning analysis on hot water ingress during the testing of water-resistant medium-voltage cables using a fiber optic strain-temperature demodulator specifically includes the following steps: Through continuous acquisition by the fiber optic strain-temperature demodulator, the strain and temperature values ​​of the composite water-blocking layer based on the distributed sensing optical cable and the distributed sensing optical cable detection of the entire line of the water-blocking medium-voltage cable were obtained in real time during the test. When the strain value exceeds the preset strain threshold but the temperature value is less than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water infiltration and water ingress due to sheath damage, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point. If only the temperature value rises above the preset temperature threshold while the strain value is below the preset strain threshold, then the water-blocking medium-voltage cable is determined to be overloaded and overheated, thus eliminating the false alarm of water ingress from the demodulator. When the strain value exceeds the preset strain threshold and the temperature value is simultaneously greater than the preset temperature threshold, it is determined that the water-blocking medium-voltage cable has water intrusion, water ingress due to sheath damage, and overload and overheating of the cable core, triggering the demodulator's moisture warning and accurately locating the heat and humidity warning anchor point.

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