Fusion tube of drop-out fuse with automatic on-off function and manufacturing method of fusion tube

Abstract

The invention discloses a drop-out fuse fusion tube with an automatic on-off function. The drop-out fuse fusion tube comprises a fusion tube body, the series connection automatic on-off branch circuit is arranged in the fusion tube body, and the series connection automatic on-off branch circuit is configured to have the following electrical characteristics that the series connection automatic on-off branch circuit is in an on state under an alternating current operation working condition and is in an off state under a direct current test transmission working condition; and the gradient potential transition and shielding integrated structure is arranged at the connecting end part of the series automatic on-off branch and the fusion tube body. An integrated shielding structure of a curved surface equipotential ring, a shielding cup and a conductive gradient coating is constructed at the end part of a fusion tube, and a continuous and controllable potential gradient is formed in a three-dimensional space by utilizing a potential transition layer, so that end part electric field distortion caused by introduction of a series automatic on-off branch is effectively eliminated; and the local field intensity peak value is obviously reduced, and the local discharge initial voltage is improved, so that the aging rate of the insulating medium is greatly delayed.

Description

Technical Field

[0001] This invention relates to the technical field of power distribution, and in particular to a drop-out fuse tube with automatic switching function and its manufacturing method. Background Technology

[0002] Drop-out fuses are the most commonly used short-circuit and overload protection switches in power distribution networks. In the daily operation and maintenance and fault finding of 10kV distribution lines, the DC high-voltage test method (using a DC test instrument for insulation testing) is a common means of determining the nature of line faults.

[0003] However, because voltage transformers (PTs) are connected in parallel in the distribution network, their primary windings exhibit low impedance characteristics to DC. During DC testing, high DC voltage can directly enter ground through the PT neutral point or leak into adjacent phases, causing test failure. Therefore, traditional operating procedures require maintenance personnel to manually climb poles to disconnect the drop-out switches of each PT one by one before testing, and then restore them after the test is completed. This is not only labor-intensive and time-consuming, but the frequent operations also increase safety risks.

[0004] To address the aforementioned issues, several automatic blocking solutions have emerged in the prior art. For example, patent document CN113517084B discloses a "DC high-voltage blocking cable," which integrates a main capacitor composed of multiple capacitor cores connected in parallel within the cable insulation sheath to achieve DC blocking and AC transmission. While these external or cable-based solutions can avoid manual operation of the PT to some extent, they often require changes to the original wiring connection structure or occupy additional installation space. Furthermore, the mechanical strength and anti-aging performance of cables during long-term outdoor operation face challenges.

[0005] To further enhance equipment integration and ease of maintenance, the industry has developed an automatic switching technology (or series automatic switching branch) that is directly integrated inside the fuse tube. This technology directly encapsulates a functional module with "AC-passing and DC-blocking" characteristics within the fuse tube of the drop-out fuse, enabling seamless "plug-and-play" replacement.

[0006] Integrating the automatic on / off branch into the confined space of the fuse tube presents new technical challenges for the insulation structure design at the tube's end: to achieve electrical connection between the automatic on / off branch and the main fuse circuit within the limited tube diameter, the end region inevitably exhibits structural features such as conductor transitions, sharp bends in the leads, and space contraction. These discontinuous metal edges and narrow electrical gaps easily lead to electric field distortion, resulting in a significant increase in local field strength and triggering corona discharge or partial discharge.

[0007] The ends of the fusible tube are typically potted with materials such as epoxy resin. In the three-way bonding region of "metal-potting compound-insulating tube wall," micro-gaps or micro-cracks are easily generated due to differences in the thermal expansion coefficients of the materials and limitations of the potting process. Under a high electric field, these defects become convergence points of electric field lines, accelerating dielectric aging and even leading to surface flashover breakdown.

[0008] The built-in automatic switching branch exhibits different impedance characteristics under various operating conditions, such as AC operation, DC testing, and lightning surges, causing the potential distribution at the terminal connection points to fluctuate drastically with the operating conditions. Without a systematic potential gradient control design, transient overvoltages can easily couple to internal low-voltage components, causing breakdown damage. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is: after the series automatic switching branch is integrated in the fuse tube of the drop-out fuse, the end connection area suffers from severe electric field distortion, low partial discharge initiation voltage and easy aging of insulating medium due to the structural complexity.

[0010] The above-mentioned technical problems are solved by the following technical solution: The present invention proposes a drop-out fuse tube with automatic switching function, comprising a fuse tube body; a series automatic switching branch disposed in the fuse tube body, the series automatic switching branch being configured to have the following electrical characteristics: presenting a conducting state under AC operation conditions and presenting an open circuit state under DC test conditions; and an integrated gradient potential transition and shielding structure disposed at the connection end of the series automatic switching branch and the fuse tube body.

[0011] In a preferred embodiment of the drop-out fuse tube with automatic switching function described in this invention: the integrated gradient potential transition and shielding structure includes: a curved equipotential ring, which is arranged around the connection terminal of the series automatic switching branch to expand the end equipotential surface; a shielding cup, which covers the lead transition area of ​​the connection terminal and is electrically connected to the curved equipotential ring; and a conductive gradient coating, which is attached to the inner wall of the end of the fuse tube body and distributed along the axial direction to achieve a smooth potential transition from high potential to insulating medium.

[0012] In a preferred embodiment of the drop-out fuse tube with automatic switching function described in this invention: the conductive gradient coating is a high-resistivity conductive material layer arranged along the axial direction; the surface resistivity of the conductive gradient coating exhibits a gradient change along the axial direction, with the lowest resistivity near the high-potential conductor side and the highest resistivity near the insulator side.

[0013] In a preferred embodiment of the drop-out fuse tube with automatic on / off function described in this invention: the conductive gradient coating is made of conductive filler containing graphite powder and silicon carbide micro powder, and the gradient distribution of the surface resistivity is controlled by changing the content of the conductive filler.

[0014] In a preferred embodiment of the drop-out fuse tube with automatic switching function of the present invention: a potential transition layer is provided between the outer edge of the curved equipotential ring and the conductive gradient coating; the potential transition layer includes a first conductive composite pad, a second conductive composite pad and a third conductive composite pad, the volume resistivity of each of the conductive composite pads increasing sequentially, so as to form a series resistance network between the curved equipotential ring and the conductive gradient coating, so that the voltage drop is distributed according to a predetermined ratio.

[0015] In a preferred embodiment of the drop-out fuse tube with automatic switching function described in this invention: the potential transition layer is divided into three sections, and the volume resistivity of the conductive composite gasket in each section gradually increases in a step-like manner.

[0016] In a preferred embodiment of the drop-out fuse tube with automatic on / off function described in this invention: the shielding cup is a thin-walled metal cup or a metallized composite cup; the edge of the shielding cup is chamfered or rounded.

[0017] In a preferred embodiment of the drop-out fuse tube with automatic switching function described in this invention: the inner edge of the curved equipotential ring is electrically connected to the terminal of the series automatic switching branch, the outer edge extends toward the inner wall of the fuse tube body, and its outer surface has a smooth curved profile.

[0018] In a preferred embodiment of the drop-out fuse tube with automatic on / off function described in this invention, an axial lead transition structure is further included; the axial lead transition structure includes a conductor arranged along the axial direction and a shielding bushing arranged coaxially with the conductor.

[0019] This invention also provides a method for manufacturing a drop-out fuse tube with automatic switching function, including segmented assembly: after assembling the leads and connectors of the series automatic switching branch, installing the curved equipotential ring and shielding cup, and finally laying the potential transition layer and conductive gradient layer on the inner wall of the end; electrical connection treatment: fixing the curved equipotential ring, shielding cup and preset equipotential points by riveting and conductive adhesive double connection; vacuum potting: placing the assembled component in a vacuum environment, performing a first vacuuming and initial curing through the preset exhaust groove at the end, and then performing a second curing at a temperature higher than the initial curing temperature to eliminate shrinkage stress.

[0020] The beneficial effects of this invention are as follows: By constructing an integrated shielding structure of curved equipotential ring, shielding cup, and conductive gradient coating at the end of the fusible tube, a continuous and controllable potential gradient is formed in three-dimensional space using a potential transition layer. This effectively eliminates the end electric field distortion caused by the introduction of series automatic switching branches, significantly reduces the local field strength peak and increases the partial discharge initiation voltage, thereby greatly delaying the aging rate of the insulating medium. In addition, this structure achieves electromagnetic decoupling between surges and internal circuits, ensuring the electrical stability of the fusible tube under various operating conditions such as AC operation, DC test delivery, and transient impact. Moreover, the overall structure is compact, and with the segmented assembly and secondary curing process, it is suitable for large-scale manufacturing and quality consistency control. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention. Wherein: Figure 1 A schematic diagram of the overall structure of the fuse tube of a drop-out fuse with automatic on / off function is shown. Figure 2 A cross-sectional view of the overall structure of the fuse tube of a drop-out fuse with automatic on / off function is shown. Figure 3 The fuse tube of a drop-out fuse with automatic on / off function is shown. Figure 2 Enlarged view of the structure at point A; Figure 4 The equivalent circuit diagram of the potential transition principle of the drop-out fuse tube with automatic on / off function is shown; Figure 5 A process flow diagram is shown for manufacturing a drop-out fuse tube with automatic on / off function. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0023] The terminology used in this invention is that which is currently widely used in the art in consideration of the function of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new technology in the art. Furthermore, specific terms may be chosen by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terms used in this specification should not be construed as simple names, but rather based on their meanings and the overall description of the invention.

[0024] Example 1 Reference Figure 1-4This embodiment provides a drop-out fuse tube with automatic switching function, including a fuse tube body 1; a series automatic switching branch 2 disposed within the fuse tube body 1, the series automatic switching branch 2 being configured to have the following electrical characteristics: it is in a conducting state under AC operation conditions and in an open state under DC test conditions; a gradient potential transition and shielding integrated structure 3 disposed at the connection end between the series automatic switching branch 2 and the fuse tube body 1. In this embodiment, the fuse tube body 1 is made of high-temperature resistant, high-mechanical-strength epoxy glass fiber wound tube, applicable to voltage levels of 12kV or 24kV; the core components of the series automatic switching branch 2 include a high-voltage rectifier diode assembly and a normally closed high-voltage vacuum relay.

[0025] The integrated gradient potential transition and shielding structure 3 includes: a curved equipotential ring 31, which is arranged around the connection terminal of the series automatic switching branch 2 to expand the end equipotential surface; a shielding cup 32, which covers the lead transition area of ​​the connection terminal and is electrically connected to the curved equipotential ring 31; and a conductive gradient coating 33, which is attached to the inner wall of the end of the fuse body 1 and distributed along the axial direction to achieve a smooth potential transition from high potential to insulating medium. The curved equipotential ring 31 and the shielding cup 32 are both made of corrosion-resistant brass H62 or aluminum alloy 6061, and their surfaces are silver-plated and polished to reduce contact resistance and surface field strength.

[0026] The conductive gradient coating 33 is a high-resistivity conductive material layer disposed along the axial direction. The surface resistivity of the conductive gradient coating 33 exhibits a gradient change along the axial direction, with the lowest resistivity near the high-potential conductor side and the highest resistivity near the insulator side. The conductive gradient coating 33 has an axial length of 50 mm to 80 mm, and its surface resistivity smoothly transitions from 1.0 x 10^4 Ω / sq at the high-potential end to above 1.0 x 10^9 Ω / sq at the insulator end.

[0027] The conductive gradient coating 33 is made of conductive filler containing graphite powder and silicon carbide micropowder. The gradient distribution of surface resistivity is controlled by changing the content of the conductive filler. The substrate material of the coating is an arc-resistant epoxy resin adhesive; the average particle size of the graphite powder is 5 μm, and the average particle size of the silicon carbide micropowder is 1 μm to 3 μm. The gradient resistivity distribution is achieved by spraying slurry with different filler ratios in 5 to 8 layers sequentially using a precision spraying process.

[0028] A potential transition layer 34 is provided between the outer edge of the curved equipotential ring 31 and the conductive gradient coating 33. The potential transition layer 34 includes a first conductive composite pad 341, a second conductive composite pad 342, and a third conductive composite pad 343, with the volume resistivity of each conductive composite pad increasing sequentially to form a series resistance network between the curved equipotential ring 31 and the conductive gradient coating 33, thereby distributing the voltage drop according to a predetermined ratio. The substrate of the conductive composite pad is methyl vinyl silicone rubber, and different volume resistivity is achieved by doping with different proportions of acetylene black. The overall pad thickness is 3mm ± 0.5mm.

[0029] The potential transition layer 34 is divided into three segments, each with a progressively increasing volume resistivity of the conductive composite pad. Specifically, the first segment is in close contact with the equipotential ring and has a volume resistivity of 1.0 x 10^3 Ω·cm; the second segment is an intermediate transition layer with a volume resistivity of 1.0 x 10^6 Ω·cm; and the third segment contacts the gradient coating with a volume resistivity of 1.0 x 10^8 Ω·cm. The axial length of each segment is approximately 10 mm.

[0030] The shielding cup 32 is a thin-walled metal cup or a metallized composite cup; the edge of the cup rim of the shielding cup 32 is chamfered or rounded. The wall thickness of the shielding cup 32 is controlled between 0.8 mm and 1.2 mm; the radius R of the rounded edge of the cup rim is not less than 1.5 mm.

[0031] The inner edge of the curved equipotential ring 31 is electrically connected to the terminal of the series automatic switching branch 2, and the outer edge extends toward the inner wall of the fuse body 1, with a smooth curved profile on its outer surface. The connection is made by cold-pressing terminals and soldering to ensure reliable electrical contact; the radius of curvature of the curved profile is designed to be greater than 5mm to ensure no visible corona discharge under power frequency withstand voltage test.

[0032] It also includes an axial lead transition structure 4; the axial lead transition structure 4 includes a conductor 41 arranged along the axial direction and a shielding bushing 42 coaxially arranged with the conductor 41. The conductor 41 is made of multi-strand tin-plated soft copper wire with a cross-sectional area of ​​not less than 2.5 mm²; the shielding bushing 42 is made of polytetrafluoroethylene (PTFE) material, and its outer diameter and the clearance between the through hole are less than 0.1 mm.

[0033] Example 2 Reference Figure 5This invention also provides a method for manufacturing a drop-out fuse tube with automatic switching function, including segmented assembly: after assembling the leads and connectors of the series automatic switching branch 2, the curved equipotential ring 31 and the shielding cup 32 are installed, and finally the potential transition layer 34 and the conductive gradient layer are laid on the inner wall of the end; electrical connection treatment: the curved equipotential ring 31, the shielding cup 32 and the preset equipotential points are fixed by riveting and conductive adhesive double connection; vacuum potting: the assembled components are placed in a vacuum environment, and a vacuum is first evacuated and initially cured through the pre-set exhaust groove at the end, followed by a second curing at a temperature higher than the initial curing temperature to eliminate shrinkage stress. In this embodiment, before assembly, all metal parts are ultrasonically degreased and wiped dry with alcohol; the conductive gradient coating 33 needs to be left to dry at 60°C for 2 hours after being laid. The conductive adhesive is a two-component silver-based epoxy conductive adhesive. After riveting, the conductive adhesive is evenly applied to the connection interface and cured at room temperature for 24 hours to ensure minimal contact resistance. The potting material is a modified epoxy resin system suitable for high-voltage insulation; the absolute pressure during vacuum potting is less than 200 Pa, and the potting temperature is 60℃; the initial curing process is to keep it in an 85℃ constant temperature oven for 4 hours; the secondary curing process is to heat it to 120℃ and keep it for 8 hours, and then slowly cool it to room temperature with the oven, with the cooling rate controlled at less than 1℃ / min.

[0034] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A drop-out fuse tube with automatic on / off function, characterized in that: Fusible tube body (1); series automatic switching branch (2) provided in the fuse tube body (1), the series automatic switching branch (2) is configured to have the following electrical characteristics: it is in a conducting state under AC operation conditions and in a closed state under DC test conditions; The gradient potential transition and shielding integrated structure (3) is set at the connection end between the series automatic switching branch (2) and the fuse body (1).

2. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: The gradient potential transition and shielding integrated structure (3) includes: a curved equipotential ring (31) arranged around the connection terminal of the series automatic switching branch (2) for expanding the end equipotential surface; A shielding cup (32) covers the lead junction area of ​​the connecting terminal and is electrically connected to the curved equipotential ring (31); A conductive gradient coating (33) is attached to the inner wall of the end of the fusible tube body (1) and distributed along the axial direction to achieve a smooth potential transition from a high potential to an insulating medium.

3. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: The conductive gradient coating (33) is a high-resistivity conductive material layer arranged along the axial direction; The surface resistivity of the conductive gradient coating (33) exhibits a gradient change along the axial direction. The resistivity of the conductive gradient coating (33) is lowest near the high-potential conductor side and highest near the insulator side.

4. The drop-out fuse tube with automatic on / off function according to claim 3, characterized in that: The conductive gradient coating (33) is made of conductive filler containing graphite powder and silicon carbide micro powder, and the gradient distribution of the surface resistivity is controlled by changing the content of the conductive filler.

5. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: A potential transition layer (34) is provided between the outer edge of the curved equipotential ring (31) and the conductive gradient coating (33). The potential transition layer (34) includes a first conductive composite pad (341), a second conductive composite pad (342), and a third conductive composite pad (343). The volume resistivity of each conductive composite pad increases sequentially to form a series resistance network between the curved equipotential ring (31) and the conductive gradient coating (33), so that the voltage drop is distributed according to a predetermined ratio.

6. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: The potential transition layer (34) is divided into three segments, and the volume resistivity of the conductive composite pad in each segment gradually increases in a step-like manner.

7. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: The shielding cup (32) is a thin-walled metal cup or a metallized composite cup; The edge of the shielding cup (32) is chamfered or rounded.

8. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: The inner edge of the curved equipotential ring (31) is electrically connected to the terminal of the series automatic switching branch (2), and the outer edge extends toward the inner wall of the fuse body (1), with a smooth curved profile on its outer surface.

9. The drop-out fuse tube with automatic on / off function according to claim 1, characterized in that: It also includes an axial lead transition structure (4); The axial lead transition structure (4) includes a conductor (41) arranged along the axial direction and a shielding bushing (42) arranged coaxially with the conductor (41).

10. A method for manufacturing a drop-out fuse tube with automatic on / off function as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Segmented assembly: After assembling the leads and connectors of the series automatic switching branch (2), install the curved equipotential ring (31) and shielding cup (32), and finally lay the potential transition layer (34) and conductive gradient layer on the inner wall of the end. Electrical connection processing: The curved equipotential ring (31) and shielding cup (32) are fixed to the preset equipotential points by riveting and conductive adhesive. Vacuum potting: The assembled components are placed in a vacuum environment and vacuumed and initially cured through the pre-set exhaust grooves at the ends. Then, a second curing is performed at a temperature higher than that of the initial curing to eliminate shrinkage stress.

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