High load current medium voltage cable with built-in circulating cooling system and method of manufacturing the same

Abstract

This invention discloses a high-current-carrying medium-voltage cable with a built-in circulating cooling system and its manufacturing method, belonging to the field of power cable technology. The cable includes, from the inside out, a built-in circulating cooling system, a conductor layer, an insulation layer, a shielding layer, and an outer sheath layer. The built-in circulating cooling system includes a central recirculation cooling channel located at the center of the cable, filled with a cooling medium. The inner wall of the central recirculation cooling channel is provided with a turbulence-enhancing structure to strengthen the turbulence of the cooling medium. A connecting structure is provided between the central recirculation cooling channel and the conductor layer. This solution enhances turbulence through the turbulence-enhancing structure on the inner wall of the central recirculation cooling channel, allows the cooling medium to diffuse radially and directly enter the secondary cooling microchannels through the connecting structure, and forms a multi-stage heat exchange network within the cooling section. This significantly increases the effective heat exchange area between the cooling medium and the conductor, and significantly improves the convective heat transfer coefficient.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, and more specifically, to a high current-carrying medium-voltage cable with a built-in circulating cooling system and a method for manufacturing the same. Background Technology

[0002] With the acceleration of urbanization and the continuous increase in the proportion of renewable energy generation, the power load density is constantly rising, placing higher demands on the current-carrying capacity of medium-voltage distribution lines. In scenarios such as urban underground power grids, large industrial parks, and renewable energy aggregation and transmission, limited laying space poses a severe challenge to traditional cable expansion methods.

[0003] Traditional medium-voltage cables primarily rely on the natural conduction of Joule heat from the conductor through the insulation layer to the outer sheath and heat exchange with the surrounding environment for heat dissipation. Their current-carrying capacity is limited by the thermal aging life threshold of the insulation material (XLPE insulation has a long-term operating temperature of 90℃). The GB / T 12706 standard clearly specifies the structure and current-carrying capacity of medium-voltage cables, but traditional designs rely on calculations based on the IEC 60287 standard, failing to consider the multi-dimensional dynamic factors in actual operation, resulting in errors typically between 15% and 25%.

[0004] Existing cable heat dissipation and current carrying capacity enhancement technologies mainly suffer from the following technical problems: (1) Traditional heat dissipation methods have a fundamental bottleneck: natural convection heat dissipation relies entirely on passive heat exchange between the outer surface of the cable and the environment, and the rate of heat accumulation is much greater than the rate of heat dissipation. Although forced air cooling has an improvement, its heat dissipation capacity is limited by the physical property that air has a low specific heat capacity. The high-performance air-cooled medium-voltage armored cables proposed in the prior art are cooled by setting a cooling pipe in the middle of the conductor and passing air or liquid refrigerant through it, but the heat exchange area between the cooling pipe and the heat source is limited, and the overall heat dissipation efficiency is still limited by the structure.

[0005] (2) Liquid cooling technology has a complex structure and is prone to leakage: The medium-voltage power cables with good heat dissipation functions that have been disclosed rely on external water tanks, circulating pumps and drive power supplies. The system is large and complex and is not suitable for conventional laying scenarios. Integrating the liquid cooling system into the medium-voltage cable faces multiple technical challenges, such as insulation breakdown caused by leakage of cooling medium, self-sustaining operation of the system, and cooling uniformity during long-distance laying.

[0006] (3) The heat dissipation scheme of phase change material has a thermal saturation bottleneck: Due to its limited heat capacity, phase change material will quickly reach thermal saturation and fail during continuous high load operation, which makes it difficult to meet the cooling requirements of medium voltage cable for long-term continuous operation.

[0007] (4) Existing built-in cooling solutions lack heat exchange capacity and temperature adaptive control capability: Most existing solutions use a single straight pipe, with a small heat exchange area between the cooling medium and the conductor, a single flow pattern, and a lack of multi-stage coordinated cooling structure design. Furthermore, they lack graded cooling strategies and adaptive control mechanisms along the cable length.

[0008] (5) Existing technologies neglect energy utilization efficiency and intelligent control: Most solutions regard cooling as a purely thermal management problem, ignoring the self-circulation potential of the cooling medium inside the cable with uneven temperature distribution, and failing to integrate thermoelectric conversion devices with the cooling system to realize waste heat recovery and drive the self-sustaining circulation of the cooling medium.

[0009] The core deficiency of existing technology is the lack of a medium-voltage cable built-in cooling system solution that can deeply integrate the cooling medium circulation with the conductor heat dissipation structure, utilize temperature gradient to drive the medium self-circulation, and supplement it with thermoelectric conversion to achieve self-sustaining operation of the system. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a high current-carrying medium-voltage cable with a built-in circulating cooling system and a method for manufacturing the same.

[0011] To solve the above problems, the present invention adopts the following technical solution: A high-current-carrying medium-voltage cable with a built-in circulating cooling system includes, from the inside out, a built-in circulating cooling system, a conductor layer, an insulation layer, a shielding layer, and an outer sheath layer. The built-in circulating cooling system includes a central recirculation cooling channel located at the center of the cable. The central recirculation cooling channel is filled with a cooling medium, and the inner wall of the central recirculation cooling channel is provided with a turbulence structure to enhance the turbulence intensity of the cooling medium. A connecting structure is provided between the central reflux cooling channel and the conductor layer. The connecting structure is used to allow the cooling medium to diffuse radially from the central reflux cooling channel into the interior of the conductor layer for heat exchange. The conductor layer is divided into multiple cooling sections along the cable axial direction, and each cooling section is interconnected through a central return cooling channel or return pipe. Each of the cooling sections is provided with a heat exchange structure for heat exchange with the cooling medium and a temperature control flow rate regulating device for adjusting the flow rate of the cooling medium according to the temperature of the cooling section.

[0012] As a further embodiment of the present invention, the turbulence structure is a spiral fin, wherein the spiral angle of the spiral fin is 25° to 45° and the fin height is 8% to 15% of the inner diameter of the central recirculation cooling channel. The spiral fin arrangement causes the cooling medium to generate forced swirling flow during the flow process, destroying the laminar boundary layer, transforming laminar flow into turbulent flow, and significantly improving the convective heat transfer coefficient.

[0013] As a further embodiment of the present invention, the connecting structure is a radially radial microchannel with a hydraulic diameter of 0.2–2.0 mm, 4–8 rows evenly distributed circumferentially, and an axial spacing of 20–50 mm; the radial length of the radially radial microchannel is 50%–70% of the conductor layer thickness. The cooling medium first obtains high turbulence intensity through the turbulence structure of the central recirculation cooling channel, and then flows into the radially radial microchannel, directly exchanging heat from inside the conductor, thus significantly increasing the heat exchange area compared to the traditional single-tube scheme.

[0014] As a further embodiment of the present invention, the cooling section is an annular cooling chamber divided by an annular metal partition, the heat exchange structure is a spiral microfin tube bundle, and the temperature control and flow regulation device is a temperature-sensing memory alloy valve. Cooling sections are set at regular intervals along the cable axis, and the cooling sections are connected in series or parallel through a central return cooling channel or return pipe.

[0015] As a further aspect of the present invention, the valve core of the temperature-sensing memory alloy valve is made of shape memory alloy, and the phase transition temperature of the memory alloy is set as the upper limit of the cable's operating temperature. When the cable temperature is lower than the phase transition temperature, the valve is in a closed or slightly open state (first opening); when the cable temperature reaches or exceeds the phase transition temperature, the valve is in an open or fully open state (second opening). This structure achieves graded adaptive cooling along the cable length. The segmented annular cooling chamber, combined with the temperature-sensing memory alloy valve, ensures that the higher the temperature section, the greater the flow rate of the cooling medium, automatically compensating for the attenuation of cooling capacity along the cable and making the temperature distribution of the entire cable more uniform.

[0016] As a further embodiment of the present invention, the conductor layer is composed of multiple irregularly shaped conductor filaments twisted together. Each irregularly shaped conductor filament has an axial through groove on its inner side. The axial through groove, together with the outer wall of the central return cooling channel or an adjacent irregularly shaped conductor filament, forms a secondary cooling microchannel. The outlet of the connecting structure is connected to the secondary cooling microchannel. This structure allows the cooling medium to flow directly into the secondary cooling microchannel after exiting the connecting structure, enabling three-dimensional heat exchange within the conductor layer. The micro-dimple array further enhances turbulence and improves the near-wall convective heat transfer coefficient.

[0017] The cross-section of the irregularly shaped conductor filament is elliptical or rhomboid, and the surface of the irregularly shaped conductor filament is distributed with an array of micro-pits. The pits have a diameter of 0.3 to 0.8 mm, a depth of 0.1 to 0.3 mm, and a spacing of 1 to 2 mm. The surface structured design enhances the fluid turbulence intensity and improves the convective heat transfer coefficient near the wall.

[0018] As a further aspect of the present invention, the gaps between the conductor layer and the central recirculation cooling channel, and between the irregularly shaped conductor filaments, are filled with a gradient porosity thermally conductive composite material. This gradient porosity thermally conductive composite material is composed of a high thermal conductivity filler and a polymer matrix. Along the radial direction of the cable, the filler volume fraction of the gradient porosity thermally conductive composite material is 50%–70% on the side closer to the central recirculation cooling channel and 20%–40% on the side farther from the central recirculation cooling channel. The gradient porosity design utilizes the characteristic that thermal conductivity increases with the filler content to construct an efficient heat conduction path radially from the heat-generating core region outwards, preferentially guiding the heat generated inside the conductor to the area through which the cooling medium flows, achieving directional heat transport "preferentially to the cold source." The thermally conductive filler is selected from boron nitride, alumina, silicon carbide, or a combination thereof, and the polymer matrix is ​​silicone rubber or epoxy resin.

[0019] As a further aspect of the invention, a thermoelectric conversion device array is provided between the insulating layer and the outer wall of the cooling section. The thermoelectric conversion device array is composed of multiple pairs of p-type and n-type semiconductor thermoelectric arms connected in series. The cold end of the thermoelectric conversion device array is in close contact with the outer wall of the cooling section, and the hot end is in close contact with the inner side of the insulating layer. A phase change heat storage material layer is provided between the cold end of the thermoelectric conversion device array and the outer wall of the cooling section. The phase change heat storage material layer has a phase change temperature of 50–65°C. During load surges, it absorbs additional heat and smooths out temperature peaks; during load declines, it releases heat to power the thermoelectric conversion devices for continuous power generation. A miniature electromagnetic drive circulation pump is installed at the end of the central recirculation cooling channel, and the output end of the thermoelectric conversion device array is electrically connected to the miniature electromagnetic drive circulation pump. This structure achieves a self-sustaining closed loop of "waste heat → electrical energy → driving cooling medium → temperature reduction," requiring no external power supply under most operating conditions.

[0020] As a further aspect of the present invention, a distributed temperature-flow sensing and control network is also included; The distributed temperature-flow sensing and control network includes an array of fiber Bragg grating temperature sensors embedded along the cable axis, miniature flow sensors located at the inlet and outlet of each cooling section, and an embedded controller located at the end of the cable. The axial spacing of the fiber Bragg grating temperature sensor array is 2 to 5 meters, and the embedded controller is electrically connected to the temperature-sensing memory alloy valve and the micro electromagnetic drive circulation pump.

[0021] The present invention also provides a method for manufacturing the above-mentioned cable, comprising the following steps: 1) Preparation of irregular conductor single wires: Using a continuous extrusion molding process, oxygen-free copper rods are extruded into irregular conductor single wires with elliptical or rhomboid cross sections. At the same time, axial through grooves are extruded on the inner side of the single wire. Then, a micro-dimple array is formed on the surface of the single wire through surface rolling or laser etching processes. 2) Fabrication of the central reflux cooling channel assembly: A tubular skeleton with an inner wall turbulence structure is fabricated using precision extrusion or 3D printing. Then, a connecting structure is fabricated on the outer wall by laser drilling or micro-electrical discharge machining. 3) Assemble the conductor layer: Arrange and twist the irregularly shaped conductor filaments around the central recirculation cooling channel. During the twisting process, inject gradient porosity thermally conductive composite material step by step to form the conductor layer and secondary cooling microchannels, and connect the outlet of the interconnected structure with the secondary cooling microchannels. 4) Install cooling sections: Annular metal baffles are installed at predetermined intervals along the cable axis. Spiral microfin tube bundles are installed in the chambers between the baffles as heat exchange structures and temperature-sensing memory alloy valves as temperature control and flow regulation devices to form multiple cooling sections. 5) Install a thermoelectric conversion system: Install a thermoelectric conversion device array around the outer wall of the cooling section, and set a phase change heat storage material layer between the cold end of the thermoelectric conversion device and the outer wall of the cooling section. Then, electrically connect the output end of the thermoelectric conversion device array to a miniature electromagnetic drive circulation pump located at the end of the central recirculation cooling channel. 6) Laying a sensing and control network: Bury a fiber Bragg grating temperature sensor array and a miniature flow sensor along the cable axis, and install an embedded controller at the cable end. Connect the embedded controller to the temperature control and flow regulation device and the miniature electromagnetic drive circulation pump. 7) Extruded outer sheath: The conductor shielding layer, insulation layer, and insulation shielding layer are extruded sequentially on the outside of the assembled cable core, then the shielding layer is braided or wrapped, and finally the outer sheath layer is extruded. 8) Filling with cooling medium and debugging: Fill the built-in circulating cooling system with binary mixed working medium through the filling port at the end of the cable, and conduct airtightness test and circulation function debugging.

[0022] As a further aspect of the present invention: the stepwise infusion includes: First, pour in the high filler content component near the central reflux cooling channel, with a filler volume fraction of 50% to 70%. After partial curing to a degree of curing of 30% to 50%, pour in the low filler content component on the outer side, with a filler volume fraction of 20% to 40%. Finally, thermoset the entire component.

[0023] Compared with the prior art, the advantages of this invention are: I. This solution enhances turbulence through the turbulence structure on the inner wall of the central recirculation cooling channel, allows the cooling medium to diffuse radially and directly enter the secondary cooling microchannels through the interconnection structure, and forms a multi-stage heat exchange network through the heat exchange structure within the cooling section. This significantly increases the effective heat exchange area between the cooling medium and the conductor, and significantly improves the convective heat transfer coefficient.

[0024] II. This solution utilizes multiple cooling sections segmented along the cable's axial direction, along with temperature and flow control devices within each section, to ensure that high-temperature sections receive a greater flow of cooling medium, automatically compensating for any decrease in cooling capacity along the cable's length. This results in a uniform temperature distribution throughout the cable, effectively preventing accelerated insulation aging caused by localized overheating.

[0025] Third, this solution utilizes a thermoelectric conversion device array placed between the insulation layer and the outer wall of the cooling section. It generates electricity using the Seebeck effect, generated by the temperature gradient in the radial direction of the cable. The generated electricity directly drives a miniature electromagnetic circulating pump, forming a self-sustaining closed loop of "waste heat → electrical energy → driving cooling → temperature reduction". Within the rated load range, the system can operate autonomously completely without external power supply.

[0026] IV. The cooling medium in this solution is a binary mixed working fluid. The high-boiling-point component undertakes continuous convective cooling, while the low-boiling-point component undergoes a phase change in the local overheated area, absorbing a large amount of heat by utilizing the latent heat of vaporization. This results in a sharp increase in the heat transfer coefficient, effectively suppressing the spread of hot spots and improving the short-term overload capacity of the cable.

[0027] V. The cooling system of this solution is completely built into the cable, without the need for external water tanks, pump stations or other auxiliary facilities. The outer diameter is only slightly larger than that of traditional cables of the same specification, making it easy to replace and use in existing laying spaces. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the built-in circulating cooling system of the present invention; Figure 3 This is a schematic diagram of the structure of the irregularly shaped conductor monofilament of the present invention; Figure 4 This is a schematic diagram of the conductor layer stranding structure of the present invention; Figure 5 This is a partial axial structural diagram of the cable of the present invention; Figure 6 This is a three-dimensional schematic diagram of the connection between the cooling section and the conductor layer of the present invention.

[0029] Explanation of the labels in the diagram: 1. Built-in circulating cooling system; 10. Cooling medium; 11. Central recirculation cooling channel; 111. Turbulence structure; 12. Connecting structure; 13. Miniature electromagnetic drive circulating pump; 2. Conductor layer; 21. Irregularly shaped conductor filament; 22. Axial through slot; 23. Micro-dimple array; 3. Insulation layer; 4. Shielding layer; 41. Conductor shielding layer; 42. Insulating shielding layer; 43. Wrapping shielding layer; 5. Outer sheath layer; 6. Cooling section; 61. Heat exchange structure; 62. Temperature control and flow regulation device; 7. Array of thermoelectric conversion devices; 8. Layer of phase change heat storage material; 9. Distributed temperature-flow sensing and control network; 91. Fiber Bragg grating temperature sensor array; 92. Miniature flow sensor; 93. Embedded controller. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] like Figure 1-6 As shown, a 100-meter-long cable with a rated voltage of 8.7 / 15kV and a nominal cross-section of 300mm² is prepared. 2 High current carrying capacity medium voltage cable with built-in circulating cooling system.

[0033] I. Preparation of irregularly shaped conductor single wires 21: A continuous extrusion molding process was used to extrude oxygen-free copper rods into irregularly shaped conductor monofilaments 21 with an elliptical cross-section, a major axis of 3.2 mm, and a minor axis of 2.4 mm. During the extrusion process, an axial groove 22 was simultaneously extruded into the inner side of the monofilament using a special die. The groove width was 1.5 mm and the depth was 1.0 mm. Subsequently, a micro-dimple array 23 was formed on the surface of the monofilament using a laser etching process. The dimples had a diameter of 0.5 mm, a depth of 0.2 mm, a circumferential spacing of 1.5 mm, and an axial spacing of 2 mm. A total of 91 irregularly shaped conductor monofilaments 21 were prepared.

[0034] II. Preparation of 11 components for the central reflux cooling channel: A tubular framework for the central reflux cooling channel 11 was fabricated using a precision extrusion process. The material was polyetheretherketone (PEEK), with an outer diameter of 15 mm, an inner diameter of 10 mm, and a wall thickness of 2.5 mm. During extrusion, an extrusion die with a spiral internal cavity structure was used to directly form the inner wall turbulence structure 111. In this embodiment, the turbulence structure 111 consists of spiral ribs with a spiral angle of 30°, a rib height of 1.2 mm (12% of the channel's inner diameter), and a rib spacing of 2.5 mm. Then, a connecting structure 12—radially radial microchannels—was fabricated on the outer wall using laser drilling. The microchannels had a diameter of 1.0 mm, were evenly distributed in 6 rows circumferentially, had an axial spacing of 20 mm, and a radial length equal to 60% of the conductor layer 2 thickness (approximately 4.5 mm).

[0035] III. Assemble conductor layer 2: Ninety-one irregularly shaped conductor wires 21 are twisted together in three layers around a central reflux cooling channel 11: an inner layer of 19 wires (pitch 12 times the conductor diameter), a middle layer of 30 wires (pitch 14 times the conductor diameter), and an outer layer of 42 wires (pitch 16 times the conductor diameter), with the twisting direction alternating layer by layer. During the twisting process, the axial groove 22 of each wire, together with the outer wall of the central reflux cooling channel 11 or the adjacent irregularly shaped conductor wire 21, forms a secondary cooling microchannel, and the outlet of the connecting structure 12 is directly connected to the secondary cooling microchannel. In addition, the conductor wires 21 are twisted into a spiral shape, so the secondary cooling microchannel also extends in a spiral shape along with the wires.

[0036] During the stranding process, a gradient porosity thermally conductive composite material is injected in stages. The thermally conductive filler is a 1:1 mass ratio mixture of boron nitride (average particle size 15 μm) and alumina (average particle size 5 μm). The polymer matrix is ​​methyl vinyl silicone rubber. The staged injection steps are as follows: first, the high filler content component (65% by volume) is injected near the central reflux cooling channel 11, and partially cured to 40% curing degree; then, the low filler content component (30% by volume) is injected on the outer side; finally, the entire assembly is thermoset and molded.

[0037] IV. Install cooling section 6: A cooling section 6 is installed every 30 meters along the cable axis, with each cooling section being 0.8 meters long. The cooling sections 6 are interconnected via a central return cooling channel 11 or a return pipe. Each cooling section 6 is divided into annular cooling chambers by annular metal partitions (6061 aluminum alloy, 0.8 mm thick). A heat exchange structure 61 is installed within each cooling section 6 chamber. This heat exchange structure is a spiral microfinned tube bundle, using copper tubes with an outer diameter of 6 mm, a fin height of 1.5 mm, and a fin spacing of 2 mm, spirally wound three times.

[0038] A temperature-controlled flow rate regulating device 62 is installed at the inlet of each cooling section 6 (i.e., on the return pipe connected to the central return cooling channel 11). This device is a temperature-sensing shape memory alloy valve. The valve core is made of nickel-titanium shape memory alloy (Ni content 50.8 at%), and its phase transformation temperature is set to 70℃ after shaping heat treatment. The valve adopts a sleeve structure, and the shape memory alloy spring drives the valve core. At room temperature, the valve opening is 30% (first opening). When the temperature reaches 70℃, the shape memory alloy undergoes a phase transformation and shrinkage, driving the valve core to open to 100% full opening (second opening).

[0039] In addition, the fabrication of temperature-sensing memory alloy valves includes: Nickel-titanium shape memory alloy wire is wound into a spring shape, and then heat-treated in a mold at a setting temperature of 550-600℃ for 30-60 minutes. After quenching, it is subjected to 3-5 cycles of hot and cold cycling within ±5℃ of the phase transformation temperature to stabilize the phase transformation temperature within the range of 65-85℃.

[0040] V. Install the thermoelectric conversion system: A thermoelectric conversion device array 7 is installed between the outer wall of the cooling section 6 and the insulation layer 3. The thermoelectric conversion devices are p-type Bi₂Te₃ (doped with Sb) and n-type Bi₂Te₂.₇Se₀.₃, with thermoelectric arm cross-sections of 1.0 mm × 1.0 mm and a height of 1.5 mm. Each device contains 20 pairs of thermoelectric arms connected in series. The cold end is attached to the outer wall of the cooling section 6 with thermally conductive adhesive, and the hot end is tightly attached to the inner side of the insulation layer 3 with a thermally conductive insulating pad (actually contacting the surface of the conductor shielding layer 41, which is extremely thin and has negligible thermal resistance, thus not affecting the thermoelectric conversion efficiency). A phase change heat storage material layer 8 is set between the cold end and the outer wall of the cooling section 6. The material is a paraffin / expanded graphite composite phase change material with a phase change temperature of 58℃ and a thickness of 1.0 mm.

[0041] Each section is equipped with 12 thermoelectric conversion devices, connected in series to form an array, with a total output voltage of approximately 2-3V. A miniature electromagnetically driven circulating pump 13 is installed at the end of the central recirculation cooling channel 11. This pump is a brushless DC miniature gear pump with a rated flow rate of 2L / min, a head of 10kPa, and a rated power of 3W. The output terminal of the thermoelectric conversion device array 7 is electrically connected to the miniature electromagnetically driven circulating pump 13 via a DC-DC boost circuit (boosted to 3V).

[0042] VI. Laying out a sensing and control network: A fiber Bragg grating temperature sensor array 91 is embedded every 2 meters along the cable axis, with a total of 50 measuring points, a center wavelength of 1525–1565 nm, and a temperature measurement accuracy of ±0.5℃. Miniature flow sensors 92 are installed at the inlet and outlet of each cooling section 6, with a range of 0.5–5 L / min and an accuracy of ±3%. An embedded controller 93 (based on an ARM Cortex-M4 core, integrating signal conditioning circuitry and a PID control algorithm) is installed at the cable end; the embedded controller 93 is electrically connected to a temperature-sensing memory alloy valve 62 and a miniature electromagnetic drive circulation pump 13.

[0043] VII. Insulation and Sheath Extrusion: Outside the assembled cable core, a three-layer co-extrusion process is used to extrude the following layers sequentially: conductor shielding layer 41 (semi-conductive cross-linked polyethylene, 1.0 mm thick, extrusion temperature 120℃), insulation layer 3 (cross-linked polyethylene XLPE, 8.0 mm thick, steam cross-linking temperature 250℃), and insulation shielding layer 42 (semi-conductive cross-linked polyethylene, 1.0 mm thick). Then, two layers of 0.1 mm thick soft copper tape are overlapped and wrapped to form a wrapped shielding layer 43 with an overlap rate of 20%. Finally, the outer sheath layer 5 (flame-retardant PVC, 3.5 mm thick, extrusion temperature 170℃) is extruded.

[0044] VIII. Cooling medium 10 filling and system commissioning: The binary mixed working fluid 10 is injected into the built-in circulating cooling system 1 through the injection port at the end of the cable. By mass, it consists of 70 parts perfluorotriethylamine and 30 parts hydrofluoroether (HFE-7100). The injection volume fills 80% to 90% of the total volume of the central reflux cooling channel 11, the connecting structure 12, the secondary cooling microchannels, and the cooling section 6, leaving 10% to 20% of the gas phase space for the phase change expansion of the cooling fluid.

[0045] After injection, an airtightness test is performed: test pressure 0.3–0.5 MPa, pressure held for 24 hours, leakage rate less than 1×10⁻⁶. -5 Pa·m 3 / s. After the cable is installed and laid, the built-in circulating cooling system 1 is activated and tested; Activation and commissioning include: replenishing the cooling medium 10 to the working level in the cooling system, starting the self-test program of the thermoelectric conversion device array 7, verifying the start-up performance of the micro electromagnetic drive circulation pump 13 under the power supply of the thermoelectric conversion device, calibrating the zero-point offset of each temperature sensor through the embedded controller 93, and setting the temperature control threshold of each segmented annular cooling chamber.

[0046] IX. Performance Testing Experiment (a) Current carrying capacity test: Test standards: GB / T 12706-2020 "Extruded insulated power cables and accessories with rated voltage of 1kV (Um=1.2kV) to 35kV (Um=40.5kV)" and IEC 60287 "Calculation of current carrying capacity of power cables".

[0047] Test conditions: laid in air, ambient temperature 40℃, conductor allowable operating temperature 90℃ (XLPE insulation); the control sample is of the same cross-section (300mm²). 2 Traditional XLPE insulated cable (without built-in cooling system).

[0048] Test method: Place the cable in a temperature-controlled constant temperature chamber (40℃±1℃), gradually increase the load current, and record the conductor temperature every 30 minutes (measured by an embedded thermocouple). When the conductor temperature stabilizes at 90℃±2℃ and does not exceed the limit for 1 hour, record the current value as the continuous current carrying capacity.

[0049] Test results: Traditional cable (without cooling): Measured continuous current carrying capacity is 648A.

[0050] The cable of this invention (with built-in cooling system in operation): the measured continuous current carrying capacity is 1015A.

[0051] The cable of this invention (cooling system off, relying solely on natural convection): the measured continuous current carrying capacity is 805A.

[0052] Conclusion: When the cooling system is running, the current carrying capacity of the cable of the present invention is increased by about 56.6% compared with the traditional cable; even when the cooling system is shut down, the current carrying capacity is still increased by about 24.2% by relying solely on the natural convection circulation of the cooling medium.

[0053] (II) Temperature distribution test: Test conditions: Load current 950A (approximately 93% of the rated current carrying capacity of the cable of this invention), continuous operation for 4 hours.

[0054] Test method: A thermocouple temperature measuring point is arranged every 5 meters along the cable axis (a total of 20 measuring points), and the built-in fiber Bragg grating temperature sensor array (91) is used for synchronous monitoring; the steady-state temperature of each measuring point is recorded.

[0055] Test results: The cable of this invention has a temperature distribution range of 79℃ to 88℃ along its entire length, with an average temperature of 84.2℃ and a standard deviation of ±4.1℃. The highest temperature point occurs at approximately 2 / 3 of the cable's length (about 65 meters from the input end), at 88℃.

[0056] For conventional cables (same load 950A): after approximately 1.5 hours of operation, the local conductor temperature exceeds 110°C, exceeding the long-term allowable operating temperature of XLPE insulation. The test was terminated to protect the equipment. At the end of the test, the cable input temperature was approximately 95°C, with the middle and later sections reaching a maximum of 112°C.

[0057] Traditional single-channel cooling cable (central straight cooling pipe, no segmented adaptive valve, same load 950A): After 4 hours of operation, the temperature distribution range along the entire length is 82℃~104℃, with a standard deviation of ±8.7℃, and the highest temperature point is located at the end of the cable (approximately 104℃).

[0058] Conclusion: The cable of this invention, through segmented adaptive cooling, has a uniform temperature distribution along its entire length, and its standard deviation is significantly better than that of traditional single-channel cooling cables. The highest temperature point is controlled below 90℃, effectively avoiding local overheating.

[0059] (III) Thermoelectric conversion self-sustaining performance test: Test conditions: Under different load currents (50%, 75%, 100%, 120% of rated current carrying capacity), record the output voltage and output power of thermoelectric conversion device array 7, as well as the power consumption of micro electromagnetic drive circulation pump 13.

[0060] Test method: An electronic load was connected to the output terminal of the thermoelectric conversion device array on the outer wall of each cooling section 6, and the open-circuit voltage and maximum output power were measured. At the same time, the actual operating voltage and current of the miniature electromagnetic drive circulation pump 13 were measured.

[0061] Test results: Note: At 50% load, the output power of the thermoelectric array is insufficient to drive the circulation pump. In this case, the circulation pump is powered by an external backup power supply or relies on natural convection for circulation.

[0062] Conclusion: At a load rate of 75% or higher, the thermoelectric conversion system can provide sufficient electrical energy to drive the micro electromagnetic drive circulation pump (9); at a load rate of 100% or higher, the output power is surplus, and it can achieve fully self-sustaining operation.

[0063] (iv) Short-time overload and phase change enhanced cooling test: Test conditions: Apply 120% of the rated load current (1218A) for 30 minutes and monitor the temperature change of the conductor.

[0064] Test method: Starting from the initial temperature (85℃, 100% load steady state), the load current is rapidly increased to 1218A, and the conductor hot spot temperature is recorded every minute (the hottest spot is monitored by a fiber Bragg grating sensor).

[0065] Test results: The cable of this invention: In the first 5 minutes after the overload begins, the temperature rises rapidly from 85°C to 92°C; thereafter the rate of temperature rise slows down significantly; by 30 minutes, the temperature stabilizes at 96°C (still below the short-term allowable limit of 105°C for XLPE insulation).

[0066] Traditional single-channel cooling cable (same cross-section, same load): The temperature rises to 102℃ within 10 minutes after the overload starts, and reaches 108℃ within 15 minutes, exceeding the allowable upper limit, and the test is terminated.

[0067] Uncooled cable: If the temperature exceeds 110°C within 5 minutes of the overload starting, the test will be terminated.

[0068] Verification of phase change enhanced cooling effect: Infrared thermal imaging observation showed that during overload, a large number of microbubbles (HFE-7100 component vaporization) appeared in the local hot spot area (temperature exceeding 61°C) inside the cable of this invention. The bubbles rose and burst in the cooling medium, enhancing local heat transfer. The heat flux density in this area was about 3.2 times higher than that in the surrounding area (measured by a heat flux meter).

[0069] Conclusion: The low-boiling-point component (HFE-7100, boiling point 61℃) in the binary mixed working fluid undergoes a phase change under overload conditions, absorbing a large amount of heat using its latent heat of vaporization, effectively suppressing hot spot temperature runaway, and enabling the cable to have excellent short-term overload capacity.

[0070] (v) Insulation performance test of cooling medium Test standard: ASTM D877 "Method for testing the dielectric strength of insulating liquids (disc electrode method)".

[0071] Test method: Take the mixed working fluid sample used in Example 1 (70 parts of perfluorotriethylamine + 30 parts of HFE-7100) and measure the dielectric strength at room temperature (25°C); then place the sample in a sealed container and accelerate aging in a constant temperature oven at 100°C for 2000 hours, and measure the dielectric strength again.

[0072] Test results: Before aging: Dielectric strength is 28.2 kV / mm.

[0073] After aging for 2000 hours: the dielectric strength is 25.6 kV / mm, a decrease of approximately 9.2%.

[0074] Conclusion: The dielectric strength of this mixed working fluid is much higher than the insulation requirements of medium-voltage cables (usually ≥15kV / mm), and it has good long-term thermal stability. Minor leakage will not cause electrical breakdown accidents.

[0075] (vi) Mechanical properties and durability testing: Test standard: Appendix D of GB / T 12706.3-2020 (bending test).

[0076] Test method: The cable of this invention is wound around a test mandrel with a diameter 12 times the outer diameter of the cable (the standard requirement is 15 times), and subjected to 1000 bending cycles (±90° bending, 10 times per minute). After the bending test, check the cooling system for leaks and whether the thermoelectric conversion device is working properly.

[0077] Test results: After 1000 bending cycles, the cable outer sheath showed no cracks, the cooling system pressure remained at 0.38 MPa (initially 0.40 MPa), and the leakage rate was <1×10⁻⁶. -5 Pa·m 3 / s; All thermoelectric conversion devices are operating normally, with no open circuits or short circuits.

[0078] Conclusion: The cable of this invention has good flexibility and durability, and meets the requirements for laying and installation.

[0079] In summary, the high-current-carrying medium-voltage cable with a built-in circulating cooling system provided by this invention can be widely used in urban underground power grids, power transmission and distribution lines in high-load-density areas, and new energy aggregation and transmission scenarios. Its manufacturing method is mature, the materials are readily available, and it does not require changes to existing cable laying methods, thus possessing excellent industrialization prospects. Through the built-in self-sustaining circulating cooling system, the cable of this invention achieves energy self-sufficiency and intelligent temperature control while increasing current carrying capacity, providing a reliable technical solution for high-density power transmission.

[0080] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A high-current-carrying medium-voltage cable with a built-in circulating cooling system, comprising, from the inside out, a built-in circulating cooling system (1), a conductor layer (2), an insulation layer (3), a shielding layer (4), and an outer sheath layer (5), wherein the shielding layer (4) comprises a conductor shielding layer (41), an insulation shielding layer (42), and a wrapping shielding layer (43), characterized in that, The built-in circulating cooling system (1) includes a central reflux cooling channel (11) located at the center of the cable. The central reflux cooling channel (11) is filled with a cooling medium (10). The inner wall of the central reflux cooling channel (11) is provided with a turbulence structure (111) to enhance the turbulence intensity of the cooling medium (10). A connecting structure (12) is provided between the central reflux cooling channel (11) and the conductor layer (2). The connecting structure (12) is used to allow the cooling medium (10) to diffuse radially from the central reflux cooling channel (11) into the interior of the conductor layer (2) for heat exchange. The conductor layer (2) is divided into multiple cooling sections (6) along the cable axial direction, and each cooling section (6) is interconnected through a central return cooling channel (11) or a return pipe; Each of the cooling sections (6) is provided with a heat exchange structure (61) for exchanging heat with the cooling medium (10) and a temperature control flow regulating device (62) for adjusting the flow rate of the cooling medium (10) according to the temperature of the cooling section (6).

2. High current capacity medium voltage cable with built-in circulation cooling system according to claim 1, characterized in that, The turbulence structure (111) is a spiral rib with a spiral angle of 25° to 45° and a rib height of 8% to 15% of the inner diameter of the central recirculation cooling channel (11).

3. High current capacity medium voltage cable with built-in circulation cooling system (1) according to claim 1, characterized in that, The connecting structure (12) is a radially radial microchannel with a hydraulic diameter of 0.5 to 2.0 mm, 4 to 8 rows evenly distributed in the circumference, and an axial spacing of 20 to 50 mm; the radial length of the radially radial microchannel is 50% to 70% of the thickness of the conductor layer (2).

4. A high ampacity medium voltage cable with a built-in circulating cooling system according to claim 1, characterized in that, The cooling section (6) is an annular cooling chamber separated by annular metal partitions. The heat exchange structure (61) is a spiral microfin tube bundle. The temperature control flow regulating device (62) is a temperature sensing memory alloy valve.

5. A high ampacity medium voltage cable with a built-in circulating cooling system according to claim 4, characterized in that, The valve core of the temperature-sensing memory alloy valve is made of shape memory alloy, and the phase transition temperature of the memory alloy is set as the upper limit of the cable operating temperature. When the cable temperature is below the phase change temperature, the valve is in the first opening position. When the cable temperature reaches or exceeds the phase change temperature, the valve is in the second opening position, which is greater than the first opening position.

6. A high ampacity medium voltage cable with a built-in circulating cooling system according to claim 1, characterized in that, The conductor layer (2) is composed of multiple irregularly shaped conductor filaments (21) twisted together. Each irregularly shaped conductor filament (21) has an axial through groove (22) on its inner side. The axial through groove (22) together with the central reflux cooling channel (11) or the outer wall of the adjacent irregularly shaped conductor filament (21) forms a secondary cooling microchannel. The outlet of the connecting structure (12) is connected to the secondary cooling microchannel. The cross-section of the irregularly shaped conductor filament (21) is elliptical or rhomboid. The surface of the irregularly shaped conductor filament (21) is distributed with a micro-dimple array (23).

7. A high ampacity medium voltage cable with a built-in circulating cooling system according to claim 6, characterized in that, The gaps between the conductor layer (2) and the central reflux cooling channel (11) and between the irregular conductor filaments (21) are filled with a gradient porosity thermally conductive composite material, which is composed of a high thermal conductivity filler and a polymer matrix. The gradient porosity thermally conductive composite material has a filler volume fraction of 50% to 70% on the side closer to the central recirculation cooling channel (11) and 20% to 40% on the side farther from the central recirculation cooling channel (11) along the radial direction of the cable. The thermally conductive filler is selected from boron nitride, alumina, silicon carbide or a combination thereof, and the polymer matrix is ​​silicone rubber or epoxy resin.

8. The high current-carrying medium-voltage cable with a built-in circulating cooling system according to claim 1, characterized in that, A thermoelectric conversion device array (7) is provided between the insulating layer (3) and the outer wall of the cooling section (6); The thermoelectric conversion device array (7) is composed of multiple pairs of p-type and n-type semiconductor thermoelectric arms connected in series. The cold end of the thermoelectric conversion device array (7) is in close contact with the outer wall of the cooling section (6), and the hot end is in close contact with the inner side of the insulating layer (3). A phase change heat storage material layer (8) is provided between the cold end of the thermoelectric conversion device array (7) and the outer wall of the cooling section (6), and the phase change heat storage material layer (8) has a phase change temperature of 50-65℃; a micro electromagnetic drive circulation pump (13) is provided at the end of the central reflux cooling channel (11), and the output end of the thermoelectric conversion device array (7) is electrically connected to the micro electromagnetic drive circulation pump (13).

9. The high current-carrying medium-voltage cable with a built-in circulating cooling system according to claim 8, characterized in that, It also includes a distributed temperature-flow sensing and control network (9); The distributed temperature-flow sensing and control network (9) includes an array of fiber Bragg grating temperature sensors (91) buried along the cable axis, miniature flow sensors (92) set at the inlet and outlet of each cooling section (6), and an embedded controller (93) set at the end of the cable. The axial spacing of the fiber Bragg grating temperature sensor array (91) is 2 to 5 meters, and the embedded controller (93) is electrically connected to the temperature-sensing memory alloy valve and the micro electromagnetic drive circulation pump (13).

10. A method for manufacturing a high-current-carrying medium-voltage cable with a built-in circulating cooling system according to any one of claims 1-9, characterized in that, Includes the following steps: 1) Preparation of irregular conductor single wire (21): Using a continuous extrusion molding process, oxygen-free copper rod is extruded into irregular conductor single wire with an elliptical or rhomboid cross section (21), and axial through grooves are extruded on the inner side of the single wire (22). Then, a micro-dimple array is formed on the surface of the single wire by surface rolling or laser etching process (23). 2) Preparation of the central reflux cooling channel (11) component: The tubular skeleton of the central reflux cooling channel (11) with an inner wall turbulence structure (111) is prepared by precision extrusion or 3D printing process, and then the connecting structure (12) is prepared on the outer wall by laser drilling or micro-electrical discharge machining. 3) Assemble the conductor layer (2): Arrange and twist the irregular conductor monofilaments (21) around the central reflux cooling channel (11). During the twisting process, inject gradient porosity thermally conductive composite material step by step to form the conductor layer (2) and secondary cooling microchannels, and connect the outlet of the connecting structure (12) with the secondary cooling microchannels. The step-by-step pouring process includes: first pouring the high-filler-content component near the central reflux cooling channel (11), with a filler volume fraction of 50% to 70%, and after partial curing to a degree of curing of 30% to 50%, then pouring the low-filler-content component on the outer side, with a filler volume fraction of 20% to 40%, and finally thermosetting the entire structure. 4) Install cooling sections (6): Set annular metal partitions at predetermined intervals along the cable axis, and install spiral microfin tube bundles as heat exchange structure (61) and temperature sensing memory alloy valves as temperature control flow regulating devices (62) in the chambers between the partitions to form multiple cooling sections (6). 5) Install a thermoelectric conversion system: Install a thermoelectric conversion device array (7) around the outer wall of the cooling section (6), and set a phase change heat storage material layer (8) between the cold end of the thermoelectric conversion device and the outer wall of the cooling section (6). Then, electrically connect the output end of the thermoelectric conversion device array (7) to the micro electromagnetic drive circulation pump (13) set at the end of the central reflux cooling channel (11). 6) Laying a sensing and control network: Bury a fiber Bragg grating temperature sensor array (91) and a miniature flow sensor (92) along the cable axis, and install an embedded controller (93) at the cable end. Connect the embedded controller (93) to the temperature control flow regulating device (62) and the miniature electromagnetic drive circulation pump (13). 7) Extrusion of outer sheath: The conductor shielding layer (41), insulation layer (3), and insulation shielding layer (42) are extruded sequentially on the outside of the assembled cable core, then the shielding layer (43) is braided or wrapped, and finally the outer sheath layer (5) is extruded. 8) Filling with cooling medium and debugging: Fill the built-in circulating cooling system (1) with binary mixed working medium (10) through the filling port at the end of the cable, and perform airtightness test and circulation function debugging.

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