A cable line branching connection device

Abstract

The application discloses a cable line branch connecting device, which comprises a mounting flange, an insulating sleeve and a high-voltage connecting assembly arranged in the insulating sleeve. The insulating sleeve adopts a shell-free integrated vacuum casting forming structure, and a gradient semi-conductive shielding layer, an E-shaped integrated forging high-voltage connecting piece and a grounding connecting piece are integrally covered in solid insulation to form a fully-closed insulation structure. The high-voltage connecting piece is in a straight-through T-shaped E-shaped structure, the main conductor arm is axially penetrated, the branch conductor arm is laterally extended, the length proportion of the branch and the main stem, the branch angle and the branch root round corner transition are limited, the branch conductor arm section gradually changing design is matched, the gradient shielding layer axially distributed non-uniformly and the solid insulation with radial dielectric constant gradient are combined to construct a multi-stage electric field regulation system, the branch area electric field is smoothly transitioned, and the local electric field concentration risk is greatly reduced. The device has compact structure, is suitable for the straight-through T-shaped connection scene of the main stem cable, has high operation reliability and excellent maintenance-free performance.

Description

Technical Field

[0001] This invention relates to the field of power transmission and distribution cable accessories, specifically to a fully enclosed, fully insulated integrated branch connection device for high-voltage cable lines, suitable for T-connection branches of main cables in scenarios such as urban underground pipe networks and industrial park distribution networks. Background Technology

[0002] With the continuous advancement of urbanization, power transmission and distribution systems are gradually shifting from overhead lines to cable lines. High-voltage cables, due to their advantages such as small footprint, strong adaptability to operating environments, and less susceptibility to external factors, are widely used in urban power grids, industrial parks, and underground utility tunnels. In actual power grid construction and renovation, it is often necessary to extend one or more branch cables from the main high-voltage cable line to meet the power supply needs of different areas or electrical loads. Therefore, the branch connection device of high-voltage cable lines has become an important component of the cable system.

[0003] Existing high-voltage cable branching connection methods mainly include overhead line jumper connections, T-junction rooms (stations), substation branch connections, and branch joints. Among these, overhead line jumper connections require multiple switching between cable and overhead lines, typically necessitating the installation of poles and related ancillary facilities, resulting in a large land area, and the cable-overhead-cable operation mode increases the uncertainty of system operation. While T-junction rooms or stations can achieve cable line branching, they usually require supporting civil engineering works, occupying large spaces, having long construction periods, and resulting in high overall investment costs. Substation branch connections offer certain advantages in operational reliability, but often require the construction or expansion of substation bays and the addition of multiple cable circuits, leading to high construction costs and complexity.

[0004] In recent years, to achieve miniaturization and integration of cable line branch connections, branch joint devices using gas-insulated or solid-insulated structures have emerged. Among them, some branch joints use SF6 gas as the insulating medium. Although the structure is relatively compact, the gas-sealed structure has high requirements for manufacturing and operation and maintenance, and there are problems such as gas leakage and environmental impact during long-term operation. In addition, such devices usually require regular gas status testing, resulting in a large workload for operation and maintenance.

[0005] Another type of solid-insulated pluggable branch connector adopts a split structure of "shell + cast insulation body". Internally, it forms a conductive path by welding independent contacts to copper rods, and the cable ends use a wedge-shaped pluggable connection. While this type of structure is convenient to install, it still has the following drawbacks: First, the split conductive structure has multiple connection interfaces, resulting in significant electric field concentration at the branch nodes and a high risk of partial discharge. Second, after long-term operation, the pluggable connection is prone to contact gaps due to thermal expansion and contraction, leading to contact resistance drift and insufficient operational reliability. Third, the shielding layer is only a uniform metal layer, located between the insulation and the shell, which cannot adapt to the electric field distortion at the branch nodes, limiting its electric field control capability. Fourth, all cable interfaces are arranged in the same direction, making it only suitable for specific laying scenarios and unable to meet the mainstream application requirements of straight-through T-connections in main lines. Therefore, it is necessary to design a fully enclosed cable line branch connection device with more optimized electric field, higher operational reliability, and adaptability to straight-through T-connection scenarios. Summary of the Invention

[0006] The purpose of this invention is to provide a cable line branch connection device to solve the problems mentioned in the background art, such as insufficient electric field control capability of existing branch joints, low reliability of split structure, and limited applicable scenarios.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A cable line branch connection device includes a mounting flange, an insulating sleeve, and a high-voltage connection assembly disposed inside the insulating sleeve. The insulating sleeve is a shell-less, integrally cast structure. During the casting process, the shielding layer, high-voltage connector, and grounding connector are integrally encapsulated in solid insulation to form a non-removable integral insulation structure. The high-voltage connector is an integrally forged E-shaped conductive component, including a main conductor arm extending axially along the insulating sleeve and a branch conductor arm extending laterally from the middle of the main conductor arm. The two ends of the main conductor arm correspond to the input and output interfaces of the main cable, respectively. The branch conductor arm forms a permanent electrical connection with the high-voltage cable conductor through a fixed crimp-type conductor connector. The effective length ratio between the branch conductor arm and the main conductor arm satisfies the following condition: ; Furthermore, the branch conductor arm is set at an angle of 90° relative to the axis of the main conductor arm; the shielding layer is embedded inside the solid insulation and is set close to the periphery of the high-voltage connector. In the radial direction, from the inside to the outside, the high-voltage connector, the shielding layer, and the solid insulation are arranged in order to actively and continuously control the electric field of the branch connection area.

[0008] Furthermore, the angle between the branch conductor arm and the axis of the main conductor arm is: Where Δθ is the allowable included angle deviation.

[0009] Furthermore, the shielding layer is a gradient semiconductive shielding layer, which is non-uniformly distributed along the axial direction of the insulating sleeve, and its equivalent conductivity parameter σ(x) satisfies: Where σ0 is the reference conductivity parameter on the high-voltage side, and f(x) is a function that decreases monotonically towards the grounding side with axial position. The variation law of the conductivity parameter matches the electric field intensity distribution in the branch connection area.

[0010] Furthermore, the minimum radial insulation thickness d between the outer surface of the high-voltage connector and the outer surface of the insulating sleeve satisfies the following relationship with the rated voltage U of the device: Where k is a safety factor related to the dielectric strength of the solid insulation.

[0011] Furthermore, a semiconducting field strength control component is installed at the connection position between the high-voltage cable and the insulating sleeve. The field strength control component is sleeved at the break point of the high-voltage cable insulation shielding layer, and one end of it is equipotentially bonded to the shielding layer inside the device, forming a smooth and continuous transition of the shielding structure.

[0012] Furthermore, the field strength control component applies axial preload through a spring clamping device to compensate for dimensional deviations caused by temperature changes.

[0013] Furthermore, the junction between the main conductor arm and the branch conductor arm is set as a rounded transition fillet, and the radius R of the fillet is ≥ 0.3 times the cross-sectional diameter of the main conductor arm.

[0014] Furthermore, the cross-sectional dimensions of the branch conductor arm of the high-voltage connector gradually decrease from the root to the end along its extension direction, and the radius of curvature of the conductor surface changes continuously along the branch direction. The cross-sectional change law is linear change, piecewise linear change, or smooth curve change, so as to weaken the sudden change of electric field in the root region of the branch.

[0015] Furthermore, the dielectric constant of the solid insulation exhibits a gradient distribution along the radial direction, with a higher dielectric constant near the high-voltage connector and a lower dielectric constant near the outer surface of the insulating sleeve, and the dielectric constant gradually decreases along the radial direction.

[0016] Furthermore, the lower end of the insulating sleeve is provided with a tail tube, which is fixedly connected to the grounding connector and forms a radial sealing structure with the outer sheath of the high-voltage cable.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. The device adopts an integrated vacuum casting structure without a shell, which encapsulates the high-voltage connectors, shielding layer and grounding connectors in solid insulating material. This eliminates the assembly interface and sealing risks of the traditional separate shell and insulation structure, and avoids the problem of unstable insulation performance caused by factors such as assembly errors and sealing aging. The device has high overall consistency and significantly improved maintenance-free performance and operational reliability.

[0018] 2. It adopts an E-shaped straight-through conductive structure formed by one-piece forging, with the main conductor running axially and the branches connected laterally by T-joints. There are no conductive connection interfaces such as welding or plugging, which eliminates the problems of interface electric field concentration and contact resistance drift of split conductive structures from the root. At the same time, by quantitatively constraining the length ratio and included angle of the branch conductors, the equipotential surface distribution in the branch connection area is more continuous, effectively reducing the phenomenon of local electric field concentration at the branch nodes and reducing the risk of partial discharge. The straight-through T-shaped layout is suitable for mainstream laying scenarios such as urban underground pipe corridors and cable trenches, and has a wider range of applications.

[0019] 3. By using large rounded corners at the branch roots and a gradually changing conductor cross-section design, the radius of curvature of the conductor surface changes continuously, weakening abrupt changes in the electric field from the source; by using an axially non-uniform gradient semi-conductive shielding layer, the electric field distribution in the branch area is actively matched, achieving a gradual and smooth transition of the electric field; combined with solid insulation with a radial dielectric constant gradient, the radial electric field intensity is further homogenized; the synergistic effect of multiple optimizations significantly improves the electrical safety margin under high-voltage operating conditions.

[0020] 4. By setting a semiconducting field strength control component at the cable interface, and cooperating with the axial preload compensation of the spring clamping device, the cable insulation shield break and the internal shielding layer of the device form a smooth and continuous transition at the same potential, effectively suppressing the electric field distortion at the cable break; the spring compensation structure can offset the dimensional deviation caused by temperature cycling, ensure the fitting stability of the field strength control structure under long-term operation, and improve the operational reliability of the interface area. Attached Figure Description

[0021] Figure 1 This is an axial cross-sectional view of the cable line branch connection device described in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the overall appearance structure of the cable line branch connection device described in Embodiment 1 of the present invention; Figure 3 This is a partial cross-sectional schematic diagram of the gradually changing cross-section structure of the branch conductor of the cable line branch connection device according to Embodiment 2 of the present invention.

[0022] Wherein: 1-Mounting flange; 2-Shielding layer; 3-High voltage connector; 4-Solid insulation; 5-Grounding connector; 6-Conductor connector; 7-Field strength control component; 8-Spring clamping device; 9-Tail tube; 10-High voltage cable. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 Reference Figure 1 and Figure 2 In one embodiment of the present invention, an integrated branch connection device for cable lines is provided to realize the electrical connection between a high-voltage main cable and at least one branch cable. The device adopts a fully enclosed, fully insulated integrated structural design, suitable for applications in urban underground high-voltage power transmission and distribution systems with high requirements for land area, operational reliability, and environmental performance.

[0025] The integrated branch connection device for cable lines mainly includes an insulating sleeve and a high-voltage connection assembly disposed inside the insulating sleeve. The insulating sleeve forms at least three interfaces along the axial direction, which are respectively used for the input of the main cable, the output of the main cable, and the connection of the branch cable. A mounting flange 1 is provided on the outer side of the insulating sleeve. The mounting flange 1 is used to fix the entire device to the mounting bracket or box to meet the usage requirements of different installation environments.

[0026] The insulating sleeve is manufactured using a vacuum pressure integrated casting process, without an external metal shell. During the casting process, the high-voltage connector 3, the grounding connector 5, and the shielding layer 2 are entirely encapsulated within the solid insulation 4, forming a non-removable, fully enclosed, integral insulating structure with no internal assembly interfaces or air gaps. The solid insulation 4 is made of epoxy resin, polypropylene, or other equivalent solid insulating materials with high dielectric strength and good mechanical properties. As a preferred embodiment, the dielectric constant of the solid insulation 4 exhibits a gradient distribution along the radial direction, with a higher dielectric constant near the high-voltage connector 3 and a lower dielectric constant near the outer surface of the insulating sleeve. This material parameter gradient further homogenizes the radial electric field. The integral casting method avoids internal assembly gaps, thereby reducing the risk of partial discharge and improving the long-term operational stability of the device.

[0027] The high-voltage connector 3, housed inside the insulating sleeve, is a single-piece forged copper conductive component with an E-shaped branch configuration. It includes a main conductor arm extending axially along the device and at least one branch conductor arm extending laterally from the middle of the main conductor arm. The junction between the main conductor arm and the branch conductor arm uses a large-radius fillet transition, with a fillet radius R ≥ 0.3 times the cross-sectional diameter of the main conductor arm, to eliminate sharp-angle electric field concentration. The two ends of the main conductor arm are electrically connected to the corresponding conductor connectors 6 at the input and output ends of the main cable, respectively. The branch conductor arm is connected to the conductor of the branch high-voltage cable 10 through the corresponding conductor connector 6, thus completing the branching of the cable line. The conductor connector 6 is a fixed crimp terminal, forming a non-removable permanent electrical connection with stable contact resistance over a long period.

[0028] To achieve a smooth transition in the electric field distribution within the branch node region, the geometric parameters between the branch conductor arm and the main conductor arm are synergistically defined. Specifically, the effective length of the branch conductor arm is Li, and the effective length of the main conductor arm is L0, satisfying the following: ; Meanwhile, the angle between the branch conductor arm and the axis of the main conductor arm is θi, which is set with 90° as the center, and deviations are allowed within the manufacturing and assembly error range, satisfying: θi = 90° ± Δθ; Wherein, Δθ is the allowable deviation angle of the branch angle, which is used to fine-tune the local electric field distribution at the branch node while ensuring the overall right-angle branch structure, so as to avoid abrupt changes in the electric field.

[0029] A shielding layer 2 and a solid insulating layer 4 are sequentially arranged radially from the inside to the outside around the high-voltage connector 3. The shielding layer 2 is a gradient semi-conductive shielding layer, which is non-uniformly distributed along the axial direction inside the insulating sleeve. The equivalent conductivity parameter σ(x) of the shielding layer 2 varies with the axial position x, and its variation law matches the spatial shape and electric field distribution of the high-voltage connector 3, satisfying the following relationship: σ(x) = σ0·f(x); Where σ0 is the reference conductivity parameter on the high-voltage side, and f(x) is a function that monotonically decreases with axial position towards the grounding side. By adjusting the axial gradient of the parameters of the shielding layer 2, the electric field strength at the cable insulation shield break and branch connection area gradually transitions along the axial direction, reducing the probability of surface discharge and partial discharge.

[0030] At the connection points between each high-voltage cable 10 and the insulating sleeve, a semi-conductive field strength control component 7 is installed. The field strength control component 7 is fitted onto the break in the insulation shielding layer of the high-voltage cable 10, with one end equipotentially bonded to the shielding layer 2 on the inner wall of the insulating sleeve, forming a smooth and continuous transition in the shielding structure. The field strength control component 7 is subjected to axial preload via a spring clamping device 8, ensuring stable contact with the corresponding structure throughout long-term operation. This compensates for dimensional deviations caused by temperature changes and guarantees the long-term stability of the field strength control effect.

[0031] A tail tube 9 is provided at the lower end of the insulating sleeve. The tail tube 9 is fixedly connected to the grounding connector 5 and forms a radial sealing structure with the outer sheath of the high-voltage cable 10 to achieve the overall sealing, moisture-proof and reliable grounding functions of the device.

[0032] To ensure the overall miniaturization of the device while meeting high-voltage insulation requirements, the minimum radial insulation thickness d between the outer surface of the high-voltage connector 3 and the outer surface of the insulating sleeve satisfies the following relationship with the rated voltage U of the device: ; Where k is a safety factor related to the dielectric strength of the selected solid insulation. By parameterizing the radial insulation thickness, the device maintains sufficient electrical safety margins at branch nodes and conductor bends.

[0033] Through the above structural design, the integrated branch connection device for cable lines in this embodiment, while maintaining a compact and miniaturized structure, constructs a multi-level collaborative electric field control system, significantly reducing the risk of partial discharge, improving the long-term reliability of the device under high-voltage operating conditions, and meeting the requirements of solid insulation, maintenance-free operation, and environmentally friendly use.

[0034] Example 2 like Figure 3 As shown, in another embodiment of the present invention, the cable line branch connection device is completely consistent with Embodiment 1 in terms of overall encapsulation structure, shielding system, interface field control structure, and grounding sealing structure. It still includes a mounting flange 1, a gradient semi-conductive shielding layer 2, a high-voltage connector 3, solid insulation 4, a grounding connector 5, a conductor connector 6, a semi-conductive field strength control component 7, a spring clamping device 8, a tail tube 9, and a high-voltage cable 10, and also adopts a fully enclosed structure formed by vacuum pressure integral casting without a shell. The core difference between this embodiment and Embodiment 1 is that the branch conductor arm of the high-voltage connector 3 adopts a cross-sectional gradient structure design. Through the continuous change of the conductor's own shape, the electric field distribution at the branch node is further optimized, and the smooth control of the electric field is achieved.

[0035] Specifically, the high-voltage connector 3 is still a one-piece forged copper conductive component, with an overall E-shaped branch configuration, including a main conductor arm running through the axial direction of the device and branch conductor arms extending laterally from the middle of the main conductor arm. The junction between the main conductor arm and the branch conductor arm still uses a large rounded corner transition, with a corner radius R ≥ 0.3 times the cross-sectional diameter of the main conductor arm, eliminating sharp-angle electric field concentration at the source. Each branch conductor arm is arranged at approximately a right angle relative to the axis of the main conductor arm, with the branch angle centered at 90°, satisfying... The deviation range.

[0036] Unlike the branch conductor arm with a constant cross-section in Example 1, the cross-sectional dimensions of the branch conductor arm in this example are not constant along its extension direction. Instead, they gradually decrease from the root end near the main conductor arm to the end end away from the main conductor arm. In this example, the cross-sectional dimensions of the branch conductor arm are set to their maximum value in the root region to maximize the radius of curvature of the conductor surface in that region, further reducing the electric field distortion at the root junction. In the end region of the branch conductor arm away from the main conductor arm, its cross-sectional dimensions gradually decrease to match the cross-section of the cable conductor, thereby making the radius of curvature of the conductor surface change continuously and smoothly along the branch extension direction. The cross-sectional variation law of the branch conductor arm can be adapted to the design based on the electric field simulation results, adopting linear variation, piecewise linear variation, or smooth curve variation, and its variation law precisely matches the electric field distribution characteristics inside the insulating sleeve.

[0037] Through the aforementioned cross-sectional gradient structure design, there are no abrupt geometric sharp corners or curvature abrupt changes in the transition region connecting the branch conductor arm to the main conductor arm. Combined with the large rounded corner transition structure at the root, this dual optimization completely avoids local electric field concentration in the branch root region. Compared to branch conductor structures with constant cross-sections, this cross-sectional gradient structure can achieve a natural transition of the electric field through the conductor's shape itself without changing the overall spatial arrangement of the branches or increasing the device volume, significantly reducing the maximum electric field intensity at the branch nodes.

[0038] Around the periphery of the high-voltage connector 3, a gradient semiconducting shielding layer 2 and a solid insulating layer 4 are sequentially arranged radially from the inside out. The shielding layer 2 is still an axially non-uniformly distributed gradient semiconducting structure, and its equivalent conductivity parameter σ(x) decreases monotonically towards the grounding side along the axial direction, with its variation law precisely matching the spatial shape and electric field distribution of the high-voltage connector 3. Because the branch conductor arm adopts a gradually changing cross-section structure, the electric field on the conductor surface in the branch root region becomes more uniform, further reducing the local electric field gradient borne by the shielding layer 2 in this region, thereby improving the overall effectiveness and long-term operational stability of the shielding structure.

[0039] As a preferred option, the solid insulation 4 in this embodiment can also adopt a radial dielectric constant gradient design, with a higher dielectric constant on the side closer to the high-voltage connector 3 and a lower dielectric constant on the side closer to the outer surface of the insulating sleeve. The dielectric constant decreases gradually along the radial direction, forming a three-level synergistic electric field control system with conductor geometry optimization and gradient shielding structure, further homogenizing the radial electric field distribution and improving the insulation margin.

[0040] At the connection points between each high-voltage cable 10 and the insulating sleeve, a semi-conductive field strength control component 7 is still installed. This component 7 is fitted onto the break in the insulation shielding layer of the high-voltage cable 10, with one end equipotentially bonded to the shielding layer 2 inside the device, forming a smooth and continuous transition in the shielding structure. The field strength control component 7 is subjected to axial preload via a spring clamping device 8, ensuring stable contact with the corresponding structure throughout long-term operation. This compensates for dimensional deviations caused by temperature cycling, guaranteeing the long-term stability of the field strength control effect. The field strength control component, in conjunction with the gradually changing cross-section structure of the branch conductor arm, ensures a gradual and smooth transition of the electric field in the branch interface area from the conductor interior to the cable insulation end, further suppressing the risk of surface discharge.

[0041] A tail pipe 9 is provided at the lower end of the insulating sleeve. The tail pipe 9 is fixedly connected to the grounding connector 5 embedded in the solid insulation and forms a radial sealing structure with the outer sheath of the high-voltage cable 10 to achieve the overall sealing, moisture-proof and reliable grounding functions of the device. The mounting flange 1 is provided on the outside of the insulating sleeve and is used to fix the entire device to the mounting bracket or box. Its structure and installation method are the same as those in Embodiment 1.

[0042] By employing the aforementioned cross-sectional gradient branch conductor structure, combined with multiple optimizations such as large rounded corner transition at the root, gradient semiconducting shielding, and radial dielectric constant gradient insulation, this embodiment achieves in-depth optimization of the local electric field distribution at the branch node without altering the overall spatial layout and branch angle. Compared to the method in Embodiment 1 that primarily relies on geometric parameter proportions to control the electric field, this embodiment further reduces the maximum electric field intensity in the branch root region through continuous changes in the conductor's own curvature, coupled with a multi-level control system. This results in a smoother and more uniform electric field distribution, thereby further improving the reliability and electrical safety margin of the cable line branch connection device under high-voltage operating conditions.

[0043] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0044] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cable line branch connection device, characterized in that, It includes a mounting flange, an insulating sleeve, and a high-voltage connection assembly disposed inside the insulating sleeve. The insulating sleeve is an integral casting structure without a shell. During the casting process, the shielding layer, high-voltage connection component, and grounding connection component are completely encapsulated in solid insulation to form an integral insulation structure that cannot be disassembled. The high-voltage connector is an integrally forged E-shaped conductive component, including a main conductor arm that runs through the insulating sleeve along the axial direction and a branch conductor arm that extends laterally from the middle of the main conductor arm. The two ends of the main conductor arm correspond to the input and output interfaces of the main cable, respectively. The branch conductor arm forms a permanent electrical connection with the high-voltage cable conductor through a fixed crimping conductor connector. The effective length ratio between the branch conductor arm and the main conductor arm satisfies: 0.6≤L i / L0≤0.85; Furthermore, the angle between the branch conductor arm and the axis of the main conductor arm is set at 90°. The shielding layer is embedded inside the solid insulation and is located close to the periphery of the high-voltage connector. From the inside to the outside in the radial direction, the high-voltage connector, the shielding layer, and the solid insulation are arranged in order to actively and continuously control the electric field in the branch connection area.

2. The cable line branch connection device according to claim 1, characterized in that, The angle between the branch conductor arm and the axis of the main conductor arm is: i i =90°±Δθ; Where Δθ is the allowable included angle deviation.

3. The cable line branch connection device according to claim 1, characterized in that, The shielding layer is a gradient semi-conductive shielding layer, which is non-uniformly distributed along the axial direction of the insulating sleeve, and its equivalent conductivity parameter σ(x) satisfies: σ(x) = σ o ·f(x); Wherein, σ0 is the reference conductivity parameter on the high-voltage side, and f(x) is a function that decreases monotonically towards the grounding side with axial position. The variation law of the conductivity parameter matches the electric field intensity distribution in the branch connection area.

4. A cable line branch connection device according to claim 1, characterized in that, The minimum radial insulation thickness d between the outer surface of the high-voltage connector and the outer surface of the insulating sleeve satisfies the following condition with respect to the rated voltage U of the device: d≥k·\sqrt{U}; Where k is a safety factor related to the dielectric strength of the solid insulation.

5. A cable line branch connection device according to claim 1, characterized in that, A semiconducting field strength control component is installed at the connection point between the high-voltage cable and the insulating sleeve. The field strength control component is sleeved at the break point of the high-voltage cable insulation shielding layer, and one end of it is equipotentially bonded to the shielding layer inside the device, forming a smooth and continuous transition of the shielding structure.

6. A cable line branch connection device according to claim 5, characterized in that, The field strength control component applies axial preload through a spring clamping device to compensate for dimensional deviations caused by temperature changes.

7. A cable line branch connection device according to claim 1, characterized in that, The junction between the main conductor arm and the branch conductor arm is set as a rounded transition fillet, and the radius R of the fillet is ≥ 0.3 times the cross-sectional diameter of the main conductor arm.

8. A cable line branch connection device according to claim 1, characterized in that, The cross-sectional dimensions of the branch conductor arm of the high-voltage connector gradually decrease from the root to the end along its extension direction. The radius of curvature of the conductor surface changes continuously along the branch direction. The cross-sectional change law is linear change, piecewise linear change, or smooth curve change, so as to weaken the sudden change of electric field in the root region of the branch.

9. A cable line branch connection device according to claim 1, characterized in that, The dielectric constant of the solid insulation exhibits a gradient distribution along the radial direction, with a higher dielectric constant on the side closer to the high-voltage connector and a lower dielectric constant on the side closer to the outer surface of the insulating sleeve, and the dielectric constant gradually decreases along the radial direction.

10. A cable line branch connection device according to claim 1, characterized in that, The lower end of the insulating sleeve is provided with a tail tube, which is fixedly connected to the grounding connector and forms a radial sealing structure with the outer sheath of the high-voltage cable.

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