Compact stress cone terminal structure for high-temperature superconducting cable

Abstract

The invention provides a compact stress cone terminal structure for a high-temperature superconducting cable, and belongs to the technical field of power cable terminals.The terminal structure comprises a stress cone body, a center insulating cylinder and a semi-conductive stress control layer, the stress cone body is arranged on the outer side of a conductor channel assembly in a sleeving mode, and the semi-conductive stress control layer is arranged on the inner surface of the stress cone body; the central insulating cylinder is arranged in the axial direction, an upper pressing structure and an upper conductor connecting piece are sequentially arranged above the central insulating cylinder, a lower supporting structure is arranged below the central insulating cylinder, the top of the central insulating cylinder is fixedly connected with the upper pressing structure, and the bottom of the central insulating cylinder supports the stress cone body through the lower supporting structure. According to the compact stress cone terminal structure for the high-temperature superconducting cable, the problems that an existing stress cone is insufficient in insulation reliability, unreasonable in electric field distribution, poor in attaching stability, short in service life and too large in size in a low-temperature environment are solved.

Description

Technical Field

[0001] This invention relates to the field of power cable termination technology, and in particular to a compact stress cone termination structure for high-temperature superconducting cables. Background Technology

[0002] High-temperature superconducting cables, with their extremely low transmission loss and ultra-large transmission capacity, have shown broad application prospects in long-distance power transmission and urban power grid upgrades, and have become one of the core transmission devices for future smart power systems. As a key component of high-temperature superconducting cable terminals and intermediate joints, the stress cone's performance directly determines the insulation safety, electric field distribution rationality, and long-term operational reliability of the cable system, making it a crucial element in ensuring the stable operation of superconducting cables.

[0003] High-temperature superconducting cables operate in a unique environment, typically within liquid nitrogen temperatures. Their terminal structures require a reliable electrical transition between the cryogenic conductor and ambient air, placing stringent demands on the material compatibility and structural design rationality of the accompanying stress cones. However, most stress cones used in high-temperature superconducting cables currently follow the design principles of traditional high-voltage cables, failing to specifically optimize for the cryogenic operating characteristics and electric field distribution of superconducting cables. This has led to numerous prominent problems in practical applications, severely restricting the performance and lifespan of high-temperature superconducting cable systems.

[0004] Existing stress cones mostly use a single silicone rubber insulation material. This type of material is prone to embrittlement at 77K liquid nitrogen temperatures, resulting in a significant decrease in elasticity. This leads to an increased gap between the stress cone and the superconducting cable insulation layer, causing local electric field concentration and significantly increasing the risk of insulation breakdown, thus failing to guarantee insulation reliability in low-temperature environments. Traditional stress cones use a linearly tapered conical surface structure, which is not optimized for the low-temperature electric field characteristics of the "conductor-insulation layer" interface of superconducting cables. This results in an electric field concentration coefficient as high as 2.8~3.2, which easily causes insulation aging during long-term operation and shortens the service life of the stress cone. At the same time, the complex design of the interface between the conductor current path and the stress control structure in some structures is prone to assembly errors, further disrupting the electric field distribution and forming new electric field concentration areas near the conductor terminals, increasing the risk of partial discharge. Furthermore, existing stress cones lack a dedicated positioning mechanism adapted to low-temperature environments, making it easy for the conical surface to shift during installation, exacerbating the stress concentration problem. Moreover, the thermal shrinkage effect of materials in low-temperature environments can further widen the gap between components, reducing the bonding stability between the stress cone and the cable insulation layer. Furthermore, some structures use a combination of stress control layers and load-bearing structures, resulting in unclear stress paths. This leads to a stress cone lifespan of only 5-8 years, far below the 30-year design life of the superconducting cable itself, severely impacting the long-term operational reliability of the entire cable system. Existing high-voltage cable terminals mostly employ conventional stress cone structures, which are bulky and hinder the miniaturization and compact layout of superconducting cable terminals, making it difficult to meet the stringent space requirements of urban substations and dense power grids.

[0005] The material selection and structural design of existing stress cones have not broken through the technical framework of traditional cable accessories. They have failed to fully take into account the low-temperature operating environment, special electric field distribution, and miniaturization requirements of superconducting cables, making them unsuitable for the long-term stable operation requirements of high-temperature superconducting cables. Summary of the Invention

[0006] The purpose of this invention is to provide a compact stress cone terminal structure for high-temperature superconducting cables, which solves the problems of insufficient insulation reliability, unreasonable electric field distribution, poor bonding stability, short service life and excessive size of existing stress cones in low-temperature environments.

[0007] To achieve the above objectives, the present invention provides a compact stress cone terminal structure for high-temperature superconducting cables. The terminal structure includes a stress cone body, a central insulating cylinder, and a semi-conductive stress control layer. The stress cone body is sleeved on the outside of the conductor channel assembly, the semi-conductive stress control layer is disposed on the inner surface of the stress cone body, the central insulating cylinder is disposed along the axial direction, an upper clamping structure and an upper conductor connector are sequentially disposed above the central insulating cylinder, a lower support structure is disposed below the central insulating cylinder, the top of the central insulating cylinder is fixedly connected to the upper clamping structure, and the bottom of the central insulating cylinder supports the stress cone body through the lower support structure.

[0008] Preferably, the terminal structure further includes a conductor channel assembly and a superconducting cable conductor. The conductor channel assembly includes a conductive transition piece and a conductor terminal. The conductor channel assembly is disposed inside the central insulating cylinder. The upper and lower ends of the conductive transition piece are fixedly connected to the conductor terminal and the superconducting cable conductor, respectively. The conductive transition piece is electrically connected to the conductor terminal and the superconducting cable conductor, respectively.

[0009] Preferably, the stress cone body is made of composite insulating material, which is a composite material of low-temperature resistant silicone rubber matrix and ceramic fiber reinforced phase. The stress cone body has an axial guide hole inside, and the stress cone body is sleeved on the outside of the superconducting cable conductor through the axial guide hole. The stress cone body has a gradually tapered surface structure inside, which is an integrated design of "front gentle cone, middle groove, and rear steep cone". The middle groove is evenly distributed along the circumference of the cone surface.

[0010] Preferably, the stress cone body also includes an elastic positioning mechanism and a heat-conducting buffer layer. The elastic positioning mechanism includes an annular elastic clamp and a positioning guide groove. The positioning guide groove is located on the inner side wall of the stress cone body and extends axially. The annular elastic clamp is embedded in the positioning guide groove. The heat-conducting buffer layer is attached to the inner side of the stress cone body and is fixedly connected to the stress cone body by a low-temperature compatible adhesive.

[0011] Preferably, the annular elastic clamp and the positioning guide groove are interference-fitted to ensure that the stress cone body is tightly attached to the outer insulation layer of the superconducting cable.

[0012] Preferably, the stress cone body is provided with a gradually tapered surface structure, which adopts a segmented variable cone angle design to adapt to superconducting cables of different voltage levels.

[0013] Preferably, the stress cone body is made of composite insulation material, which is a composite of low-temperature epoxy resin and glass fiber, to meet higher mechanical strength requirements.

[0014] Therefore, the present invention adopts the above-mentioned compact stress cone termination structure for high-temperature superconducting cables, and the technical effects are as follows: 1. Improve insulation reliability in low-temperature environments: The stress cone body adopts a composite material of low-temperature resistant silicone rubber matrix and ceramic fiber reinforcement (or low-temperature epoxy resin and glass fiber composite material), which overcomes the defects of traditional single silicone rubber being prone to embrittlement and elastic decay in the 77K liquid nitrogen temperature range, ensuring the stability of the material structure at low temperatures and avoiding cracks or gaps in the insulation layer due to material failure.

[0015] 2. Optimize electric field distribution and reduce aging and discharge risks: The gradual conical surface structure with "front section gentle cone, middle section groove and rear section steep cone" is specially optimized for the low temperature electric field characteristics of the "conductor-insulation layer" interface of superconducting cables. Compared with the traditional linear gradual conical surface, the electric field concentration coefficient can be significantly reduced from 2.8 to 3.2, avoiding insulation aging caused by excessive local electric field.

[0016] 3. Enhanced fit stability and suppression of stress concentration: The built-in elastic positioning mechanism, through interference fit design, offsets the gap expansion caused by material thermal shrinkage in low-temperature environments, ensuring that the stress cone body is tightly fitted to the outer insulation layer of the superconducting cable and avoiding cone surface displacement.

[0017] 4. Extend service life and match the design life of the cable body: The reinforced design of the composite insulation material improves the mechanical strength and aging resistance of the material, and the electric field uniformity design reduces the aging loss of the insulation layer. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of a compact stress cone terminal structure for high-temperature superconducting cables according to the present invention; Figure 2 This is a cross-sectional view of the overall structure of a compact stress cone terminal structure for high-temperature superconducting cables according to the present invention.

[0019] Figure Labels 1. Upper conductor connector; 2. Upper clamping structure; 3. Central insulating cylinder; 4. Conductor channel assembly; 5. Stress cone body; 6. Semi-conductive stress control layer; 7. Lower support structure. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Example 1 like Figures 1 to 2 As shown, this invention proposes a compact stress cone termination structure specifically designed for high-temperature superconducting cables. This structure, through the ingenious design of composite insulation materials, the clever layout of a gradual electric field control structure, the precise application of an elastic positioning compensation mechanism, and comprehensive consideration of thermal conductivity buffer protection design, successfully overcomes the bottlenecks of traditional stress cone technology, providing a solid guarantee for the stable operation of high-temperature superconducting cables.

[0023] The stress cone terminal structure is meticulously assembled from several key components, mainly including conductor terminals, conductive transition pieces, a central insulating cylinder 3, a stress cone body 5, a semi-conductive stress control layer 6, an elastic positioning mechanism, a thermally conductive buffer layer, an upper conductor connector 1, an upper clamping structure 2, and a lower support structure 7. Specifically, the conductive transition piece, acting as a bridge for current transmission, cleverly connects the conductor terminals and the superconducting cable conductor, forming a continuous conductor channel assembly 4 that runs through the central insulating cylinder 3, ensuring smooth current transmission. The stress cone body 5 is fitted onto the outside of the conductor channel assembly 4, and its inner surface is carefully fitted with a semi-conductive stress control layer 6. This design enables gradual control of the electric field, effectively dispersing the concentrated electric field at the interface between the conductor and the insulating layer, and improving the uniformity of the electric field. Below the upper conductor connector 1 is an upper clamping structure 2. The central insulating cylinder 3 is stably positioned axially, its upper end tightly connected to the upper clamping structure 2, while its lower end is securely supported by the lower support structure 7, resulting in a compact and stable overall structure.

[0024] The stress cone body 5, as the core component of this structure, consists of a composite insulation body and a gradient conical structure. The composite insulation body uses a composite material of "low-temperature resistant silicone rubber matrix and ceramic fiber reinforcement," with the ceramic fiber content controlled between 15% and 20%. This material ensures both elasticity at low temperatures and sufficient mechanical strength. Simultaneously, axial guide holes are provided inside the composite insulation body to facilitate the installation of the superconducting cable conductor. For scenarios requiring higher mechanical strength, the composite insulation material can be flexibly replaced with a "low-temperature epoxy resin and glass fiber composite" material to meet the requirements of different operating conditions. The gradient conical structure is located on the outside of the composite insulation body and adopts an integrated design of "a gentle front cone (cone angle 15° to 20°), a middle groove (depth 3 to 5 mm), and a steep rear cone (cone angle 25° to 30°)." The grooves are evenly distributed along the circumference of the conical surface, with 4 to 6 grooves. This design effectively disperses the concentrated electric field at the interface between the conductor and the insulation layer, improving the uniformity of the electric field. If it is necessary to adapt to superconducting cables of different voltage levels, the conical structure can also be replaced with a segmented variable cone angle design, which is compatible with superconducting cables from 10kV to 500kV, demonstrating extremely high flexibility and adaptability.

[0025] The elastic positioning mechanism is ingeniously composed of a ring-shaped elastic clamp and a positioning guide groove. The positioning guide groove is located on the inner wall of the composite insulation body and extends axially, providing precise positioning guidance for the ring-shaped elastic clamp. The ring-shaped elastic clamp, made of low-temperature resistant and elastically stable titanium alloy, is embedded in the guide groove. Through an interference fit, this mechanism ensures a tight fit between the composite insulation body and the superconducting cable insulation layer, effectively compensating for thermal shrinkage gaps at low temperatures and ensuring that the fit gap is controlled within ≤1mm, thereby guaranteeing the stability and reliability of the structure.

[0026] The thermally conductive buffer layer uses a PPLP film with a thickness of 0.8 to 1.2 mm, which is tightly adhered to the inside of the composite insulation body and fixedly connected to the composite insulation body by a low-temperature compatible adhesive. This design can significantly reduce the damage to the insulation body caused by thermal shock during cable operation, while reducing interfacial contact resistance and improving the overall performance of the cable.

[0027] The upper conductor connector 1 is made of copper and silver-plated, ensuring good conductivity and improving corrosion resistance. It is cylindrical with an external threaded interface at the top for easy connection to external electrical equipment, and an annular boss at the bottom for positioning with the upper clamping structure 2. The upper clamping structure 2 is made of high-strength aluminum alloy or stainless steel and has an annular design. It fixes the central insulating cylinder 3 and the stress cone body 5 through axial constraint, ensuring structural stability. The central insulating cylinder 3 is made of low-temperature epoxy resin and is cylindrical with an axially continuous structure (wall thickness 10 to 15 mm), serving multiple functions including axial support, insulation, and positioning constraint. The lower support structure 7 is made of high-strength stainless steel and has an annular base shape. It stabilizes the stress cone body 5 and forms an axial constraint with the upper clamping structure 2, together creating a stable support system. In addition, the auxiliary connection materials were carefully selected, including low-temperature compatible adhesives (bonding strength ≥2MPa), insulating fillers (used to fill gaps and improve insulation performance), and low-temperature resistant insulating tape (used to wrap weld joints to enhance protection). The selection of these materials provides a strong guarantee for the stability and reliability of the structure.

[0028] During assembly, the connection methods of each component were carefully designed. The upper conductor connector 1 is positioned and tightened against the upper clamping structure 2 via an annular boss, and is circumferentially fixed with 4 to 6 bolts at equal intervals to ensure the stability of the connection. The lower groove of the upper clamping structure 2 is embedded into the upper end of the central insulating cylinder 3 and fixed with low-temperature compatible adhesive, further enhancing the overall integrity of the structure. The lower end of the central insulating cylinder 3 is embedded into the upper groove of the lower support structure 7, and is also circumferentially fixed with bolts. The support surface of the lower support structure 7 is tightly abutted against the lower end of the stress cone body 5 to ensure the stable support of the structure. The conductor channel assembly 4 passes through the axial center hole of the central insulating cylinder 3. The two are fitted with a clearance, with the clearance controlled between 2 and 3 mm. The clearance is filled with insulating filler to improve insulation performance. The lower end of the conductive transition piece is welded and fixed to the superconducting cable conductor. The weld is wrapped with low-temperature resistant insulating tape to prevent damage to the weld and enhance protection. The stress cone body 5 is fitted onto the outside of the conductor channel assembly 4. Its inner wall and the outer wall of the conductor channel assembly 4 are fitted with a clearance, with the clearance controlled within ≤1mm. This is achieved through axial constraint by the upper clamping structure 2 and the lower support structure 7. The semi-conductive stress control layer 6 is tightly adhered to the inner surface of the stress cone body 5, ensuring no loosening, air bubbles, or other defects. The thermally conductive buffer layer is fixedly connected to the inner side of the composite insulation body using a low-temperature compatible adhesive, ensuring effective thermal buffering.

[0029] During assembly, each component is first cleaned and pre-treated to ensure that the connection surfaces are free of impurities, oil, and other contaminants. Then, the conductive transition piece is fixedly connected to the conductor terminal to form the conductor channel assembly 4, which passes through the central insulating cylinder 3. Insulating filler is used to fill the gaps to improve insulation performance. Next, the upper end of the central insulating cylinder 3 is embedded into the groove at the lower end of the upper clamping structure 2 and fixed with a low-temperature compatible adhesive. Then, the upper clamping structure 2 is fixedly connected to the upper conductor connector 1 using bolts. After attaching a thermally conductive buffer layer to the inside of the composite insulating body and embedding an annular elastic clamp, the stress cone body 5 is fitted onto the outside of the conductor channel assembly 4. The lower end of the central insulating cylinder 3 is then embedded into the groove of the lower support structure 7 and fixed with bolts, ensuring a tight fit between the lower support structure 7 and the lower end of the stress cone body 5. Finally, the conductive transition piece is welded to the superconducting cable conductor (the weld is wrapped with insulating tape to enhance protection), and the upper conductor connector 1 is connected to the external electrical equipment, completing the overall assembly.

[0030] During operation, the current is smoothly transmitted axially through the conductor channel assembly 4. The stress cone body 5 and the semi-conductive stress control layer 6 expand and homogenize the electric field at the terminal, effectively improving the uniformity of the electric field. The upper clamping structure 2 applies axial constraint force to the stress cone body 5 through the central insulating cylinder 3, ensuring that the structure can still operate stably under complex working conditions.

[0031] Therefore, the present invention adopts the above-mentioned compact stress cone terminal structure for high-temperature superconducting cables. It achieves electric field control through a composite insulation body and a gradually tapered surface structure. It combines an elastic positioning mechanism to compensate for the low-temperature thermal shrinkage gap and uses a thermally conductive buffer layer to reduce thermal shock damage. It is supplemented by components such as conductor terminals, conductive transition parts, central insulation cylinder, upper conductor connector, upper clamping structure and lower support structure. Through precision assembly, a compact integrated structure is formed to ensure smooth current transmission, uniform electric field distribution and stable structural operation, thus breaking through the bottleneck of traditional stress cone technology.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A compact stress cone termination structure for high-temperature superconducting cables, characterized in that, The terminal structure includes a stress cone body, a central insulating cylinder, and a semi-conductive stress control layer. The stress cone body is sleeved on the outside of the conductor channel assembly. The semi-conductive stress control layer is disposed on the inner surface of the stress cone body. The central insulating cylinder is disposed along the axial direction. An upper clamping structure and an upper conductor connector are disposed sequentially above the central insulating cylinder. A lower support structure is disposed below the central insulating cylinder. The top of the central insulating cylinder is fixedly connected to the upper clamping structure. The bottom of the central insulating cylinder supports the stress cone body through the lower support structure.

2. The compact stress cone termination structure for high-temperature superconducting cables according to claim 1, characterized in that, The terminal structure also includes a conductor channel assembly and a superconducting cable conductor. The conductor channel assembly includes a conductive transition piece and a conductor terminal. The conductor channel assembly is installed inside the central insulating cylinder. The upper and lower ends of the conductive transition piece are fixedly connected to the conductor terminal and the superconducting cable conductor, respectively. The conductive transition piece is electrically connected to the conductor terminal and the superconducting cable conductor, respectively.

3. The compact stress cone termination structure for high-temperature superconducting cables according to claim 1, characterized in that, The stress cone body is made of composite insulating material, which is a composite material of low-temperature resistant silicone rubber matrix and ceramic fiber reinforcement. The stress cone body has an axial guide hole inside, and the stress cone body is sleeved on the outside of the superconducting cable conductor through the axial guide hole. The stress cone body has a gradient cone structure inside, which is an integrated design of "front gentle cone, middle groove and rear steep cone". The middle groove is evenly distributed along the circumference of the cone surface.

4. The compact stress cone termination structure for high-temperature superconducting cables according to claim 3, characterized in that, The stress cone body also includes an elastic positioning mechanism and a heat-conducting buffer layer. The elastic positioning mechanism includes an annular elastic clamp and a positioning guide groove. The positioning guide groove is located on the inner side wall of the stress cone body and extends axially. The annular elastic clamp is embedded in the positioning guide groove. The heat-conducting buffer layer is attached to the inner side of the stress cone body and is fixedly connected to the stress cone body by a low-temperature compatible adhesive.

5. A compact stress cone termination structure for high-temperature superconducting cables according to claim 4, characterized in that, The interference fit between the annular elastic clamp and the positioning guide groove ensures that the stress cone body is tightly bonded to the outer insulation layer of the superconducting cable.

6. The compact stress cone termination structure for high-temperature superconducting cables according to claim 1, characterized in that, The stress cone body is equipped with a gradually tapered surface structure, which adopts a segmented variable cone angle design to adapt to superconducting cables of different voltage levels.

7. The compact stress cone termination structure for high-temperature superconducting cables according to claim 1, characterized in that, The main body of the stress cone is made of composite insulation material, which is a composite of low-temperature epoxy resin and glass fiber, to meet the requirements of higher mechanical strength.

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