Full-range drop-out fuse

Abstract

The invention discloses a full-range drop-out fuse which comprises a base, the upper end and the lower end of the base are fixedly connected with an upper contact seat and a lower contact seat respectively, and a fuse carrier is installed between the upper contact seat and the lower contact seat. The fuse carrier is of a split type and comprises a current limiting part and a spraying part which are connected with each other in a detachable mode, and a first fuse wire in the current limiting part and a second fuse wire in the spraying part are connected between the upper contact seat and the lower contact seat in series. The fuse carrier comprises a current limiting part and an injection part which are connected in series, and has the advantages that a current limiting type fuse limits peak current under large fault current and does not inject combustible materials, and an injection type fuse is reliably switched on and off under the condition of small fault current, so that full-range fault current protection is realized; and meanwhile, the system has the advantages of good compatibility, low improvement cost and the like.

Description

Technical Field

[0001] The invention relates to a drop-out type fuse, in particular to a full-range drop-out type fuse. Background Art

[0002] Dropout fuses are the most commonly used short-circuit protection switches for 10kV distribution line branches and distribution transformers. Installed on distribution line branches, they effectively minimize the scope of power outages. Their distinct disconnection point also functions as an isolating switch, providing a safe operating environment for maintenance areas. Currently, common dropout fuses primarily include ejector and current-limiting types, but both have limitations in their fault current interrupting capacity.

[0003] An ejector fuse consists of a fuse base, a fuse carrier, and a fuse element. The fuse base serves as the primary support, connecting the upper incoming and lower outgoing lines of the distribution line. The fuse carrier supports the fuse element and connects the upper and lower contacts of the base. As the core component, the fuse element within it determines the circuit's protection characteristics. Its breaking principle is that when the circuit current exceeds the fuse element's rated current, the fuse element heats and melts, and the fuse element is disconnected by a retaining spring at the lower end of the fuse carrier. However, while this structure can reliably disconnect the fuse under low current conditions, it can fail to effectively disconnect the fuse under high fault current conditions due to the high arc energy and persistent arcing.

[0004] The external structure of a current-limiting fuse is similar to that of an ejector type, but its internal fuse consists of multiple fuse elements connected in parallel and wound around a ceramic quartz cylinder, surrounded by quartz sand. When the current exceeds the rated value, the weak part of the fuse element melts, and the high temperature simultaneously crystallizes the quartz sand, filling the gap and extinguishing the arc. This structure offers the advantage of rapid interruption of high short-circuit currents. However, with low fault currents (slightly above the rated current but insufficient to melt the quartz sand), the internal temperature rise of the fuse and the external heat dissipation reach a balance, resulting in failure to open normally.

[0005] It can be seen that the existing ejector fuses and current-limiting fuses are unable to achieve reliable interruption of the full range of currents: the ejector fuse has difficulty in handling large fault currents, while the current-limiting fuse has insufficient response capability to small fault currents. Summary of the Invention

[0006] The present invention provides a full-range drop-out fuse, the purpose of which is to solve the problem that the existing drop-out fuse cannot achieve reliable current interruption in the full range.

[0007] The technical solutions of the present invention are as follows: A full-range drop-out fuse includes a base, with an upper contact seat and a lower contact seat fixedly connected to the upper and lower ends of the base respectively, and a fuse carrier installed between the upper and lower contact seats. The fuse carrier is a split type, including a current limiting part and an ejection part that are detachably connected to each other, and a first fuse in the current limiting part and a second fuse in the ejection part are connected in series between the upper contact seat and the lower contact seat.

[0008] As a further improvement of the full-range drop-out fuse, the detachable connection is a threaded connection.

[0009] As a further improvement of the full-range drop-out fuse, the current limiting part and the ejection part further realize a conductive connection between the first fuse and the second fuse through a detachable connection.

[0010] As a further improvement to the full-range drop-out fuse, the current limiting portion includes a first tube body, an upper metal seat mounted on the upper end of the first tube body, a lower metal seat mounted on the lower end of the first tube body, a ceramic quartz column mounted inside the first tube body, and the first fuse wound around the outside of the ceramic quartz column; the space between the first tube body and the ceramic quartz column is filled with quartz sand; The upper metal seat is used to be conductively connected to the upper contact piece in the upper contact seat; the upper end of the first fuse is connected to the upper metal seat, and the lower end is connected to the lower metal seat; the lower metal seat is used to be detachably connected to the upper end of the injection part.

[0011] As a further improvement of the full-range drop-out fuse: a tripper is also installed at the upper end of the current limiting part; the tripper includes a rotating buckle plate buckled with the bottom end of the limit plate of the upper contact seat and a striker installed in the upper metal seat for striking the rotating buckle plate.

[0012] As a further improvement of the full-range drop-out fuse: the rotating buckle plate is installed on the upper metal seat by a rotating connection, and a first torsion spring is also installed on the upper metal seat. The first torsion spring is used to push the rotating buckle plate so that its left end maintains contact with the limit plate located above.

[0013] As a further improvement of the full-range drop-out fuse, the striker includes a metal shell installed in an upper metal base, a striker column installed in the metal shell, a compression spring installed in the metal shell for pushing the striker column upward, and a tensioning wire whose upper end is connected to the lower end of the striker column and whose lower end is fixedly connected to the insulating block in the inner hole of the ceramic quartz column; the tensioning wire is connected in parallel with the first fuse between the upper metal base and the lower metal base.

[0014] As a further improvement of the full-range drop-out fuse, the striker is made of a conductive material and contacts the metal housing, thereby achieving a conductive connection with the upper metal seat; The lower end of the tensioning wire is also electrically connected to the lower metal seat through a steel wire arranged in the inner hole of the ceramic quartz column.

[0015] As a further improvement of the full-range drop-out fuse: the ejection portion includes a second tube body, the second tube body is made of a conductive material, and the upper end is threadedly connected to the lower metal seat; A countersunk hole is provided at the upper end of the inner hole of the second tube body, in which a metal block is provided. The upper end of the second fuse passes through the auxiliary arc extinguishing tube and is connected to the metal block to achieve conductive connection with the second tube body, and the lower end extends from the lower end of the second tube body.

[0016] As a further improvement of the full-range drop-out fuse, a rotating frame is mounted on the outer side of the lower end of the second tube body by a rotating connection, and a hanging shaft is provided on the rotating frame, and the hanging shaft cooperates with the hanging frame on the lower contact seat; A fixing hook is further provided on the outer side of the lower end of the second tube; a flip plate is also mounted on the rotating frame via a rotatable connection, and the flip plate is L-shaped; the lower end of the second fuse passes around the second plate of the flip plate, causing the end of the first plate of the flip plate to be hooked to the fixing hook, and then is electrically fixedly connected to the rotating frame via a stud; a second torsion spring is also mounted on the rotating frame for pushing the flip plate to separate the first plate from the fixing hook; The rotating frame is made of conductive material and contacts the lower contact piece on the lower contact seat to achieve conductive connection.

[0017] Compared with the prior art, the present invention has the following positive effects: 1. The fuse carrier of the present invention includes a current limiting part and an ejection part connected in series. It has the advantages of limiting the peak current under large fault current of the current limiting fuse without ejecting combustible materials, and reliable disconnection of the ejection fuse under small fault current, thereby realizing full-range fault current protection.

[0018] 2. The fuse carrier of the present invention adopts a split series structure, and its size is compatible with the current standardized fuse base. During implementation, only the fuse carrier needs to be replaced, and the modification cost is low.

[0019] 3. The selection criteria for key components such as fuses in the present invention are consistent with those for traditional fuses, and designers do not need to reselect them.

[0020] 4. The tripper at the top of the current limiting part and the rotating frame mechanism at the bottom of the injection part can accurately trigger the drop of the fuse carrier, and the two do not interfere with each other. Even if both sides are triggered at the same time, they can still fall normally. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is one of the three-dimensional diagrams of the present invention; Figure 2 for Figure 1 A partial enlarged view of part A; Figure 3 This is the second stereogram of the present invention; Figure 4 for Figure 3 A partial enlarged view of part B; Figure 5 for Figure 3 A partial enlarged view of part C in the middle; Figure 6 is a cross-sectional view of the present invention; Figure 7 for Figure 6 A partial enlarged view of part D in the middle; Figure 8 for Figure 6 A partial enlarged view of part E in the middle; Figure 9 for Figure 6 A partial enlarged view of part F in the middle.

[0022] Reference numerals include: 1. Base; 2. Upper contact seat; 3. Melt carrier; 4. Lower contact seat; 2-1. Upper contact piece; 2-2. Guide frame; 2-3. Limiting plate; 3-1. Upper metal seat; 3-2. Rotating buckle plate; 3-3. First tube body; 3-4. First torsion spring; 3-5. Second tube body; 3-6. Fixing hook; 3-7. Rotating frame; 3-8. Hanging shaft; 3-9. Flip plate; 3-10. Metal shell; 3-11. Impact column; 3-12. Compression spring; 3-13. Tension wire; 3-14. Insulation block; 3-15. Steel wire; 3-16. First fuse; 3-17. Ceramic quartz column; 3-18. Quartz sand; 3-19. Lower metal seat; 3-20. Metal block; 3-21. Auxiliary arc-extinguishing tube; 3-22. Second fuse; 4-1. Mounting frame. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all the embodiments.

[0024] like Figure 1 、 Figure 3 and Figure 6 A full-range drop-out fuse includes a base 1 with a central terminal that can be mounted on a standard angle steel crossarm, serving as both a support and grounding point for the entire device. The upper and lower ends of the base 1 are provided with an inlet and outlet terminal, respectively, and are fixedly connected to an upper contact block 2 and a lower contact block 4, respectively. The upper contact block 2 and the lower contact block 4 are electrically connected to the inlet and outlet terminals, respectively, with a fuse carrier 3 mounted between them.

[0025] The fuse carrier 3 is a split-type component, consisting of a current-limiting portion and an ejection portion, each of which is approximately half the length of a standard fuse carrier. The assembled length is the same as that of a standard fuse carrier. The first fuse in the current-limiting portion and the second fuse in the ejection portion are connected in series between the upper contact seat 2 and the lower contact seat 4. In this embodiment, the detachable connection is a threaded connection. In other optional embodiments, the detachable connection can be achieved through a snap-fit ​​connection, a shaft-hole fit combined with a set screw, or other methods.

[0026] Furthermore, the current limiting portion and the injection portion also achieve a conductive connection between the first fuse 3 - 16 and the second fuse 3 - 22 through a detachable connection.

[0027] The specific structure is: like Figure 2 、 Figure 4 、 Figure 6 、 Figure 7 and Figure 8 The current limiting portion includes a first tube body 3-3, an upper metal seat 3-1 mounted at the upper end of the first tube body 3-3, a lower metal seat 3-19 mounted at the lower end of the first tube body 3-3, a ceramic quartz column 3-17 mounted inside the first tube body 3-3, and the first fuse 3-16 wrapped around the outside of the ceramic quartz column 3-17. The first tube body 3-3 is an epoxy tube, and the space between the first tube body 3-3 and the ceramic quartz column 3-17 is filled with quartz sand 3-18.

[0028] The upper metal seat 3-1 is used for conductive connection with the upper contact piece 2-1 in the upper contact seat 2. The upper end of the first fuse 3-16 is connected to the upper metal seat 3-1 and the lower end is connected to the lower metal seat 3-19. The lower metal seat 3-19 is used for threaded connection with the upper end of the injection part.

[0029] Furthermore, a trip device is installed at the upper end of the current limiting portion. The trip device includes a rotating clip plate 3-2 that is buckled with the bottom end of the limit plate 2-3 of the upper contact seat 2, and a striker installed in the upper metal seat 3-1 for striking the rotating clip plate 3-2. The rotating clip plate 3-2 is mounted on the upper metal seat 3-1 by a rotating connection. The upper metal seat 3-1 is also mounted with a first torsion spring 3-4, which is used to push the rotating clip plate 3-2 so that its left end remains in contact with the limit plate 2-3 located above. The striker includes a metal shell 3-10 installed in the upper metal seat 3-1, a striker column 3-11 installed in the metal shell 3-10, a compression spring 3-12 installed in the metal shell 3-10 for pushing the striker column 3-11 upward, and a tensioning wire 3-13 whose upper end is connected to the lower end of the striker column 3-11 and whose lower end is fixedly connected to the insulating block 3-14 in the inner hole of the ceramic quartz column 3-17. The impact column 3-11 is made of conductive material and is in contact with the metal shell 3-10, so that the tensioning wire 3-13 is conductively connected to the upper metal seat 3-1. The lower end of the tensioning wire 3-13 is also conductively connected to the lower metal seat 3-19 through the steel wire 3-15 arranged in the inner hole of the ceramic quartz column 3-17, and finally the tensioning wire 3-13 and the first fuse 3-16 are connected in parallel between the upper metal seat 3-1 and the lower metal seat 3-19.

[0030] like Figure 5 、 Figure 6 、 Figure 8 and Figure 9 The injection part includes a second tube body 3-5, the second tube body 3-5 is made of conductive material, and the external thread at the upper end is connected to the internal thread at the bottom of the lower metal seat 3-19.

[0031] A countersunk hole is provided at the upper end of the inner hole of the second tube body 3-5, in which a metal block 3-20 is provided. The upper end of the second fuse 3-22 passes through the auxiliary arc extinguishing tube 3-21 and is connected to the metal block 3-20 to achieve a conductive connection with the second tube body 3-5, and the lower end extends from the lower end of the second tube body 3-5.

[0032] Furthermore, a rotating frame 3-7 is rotatably mounted on the outer side of the lower end of the second tube 3-5. A hanging shaft 3-8 is provided on the rotating frame 3-7, which engages with the hanging frame 4-1 on the lower contact seat 4. A fixing hook 3-6 is also provided on the outer side of the lower end of the second tube 3-5. An L-shaped flap 3-9 is also rotatably mounted on the rotating frame 3-7. The lower end of the second fuse 3-22 passes around the second plate of the flap 3-9, allowing the end of the first plate of the flap 3-9 to engage the fixing hook 3-6. The end of the second fuse 3-22 is then electrically fixedly connected to the rotating frame 3-7 via a stud. A second torsion spring is also mounted on the rotating frame 3-7 to push the flap 3-9 away from the first plate of the flap 3-9 and disengage the fixing hook 3-6. The rotating frame 3-7 is made of a conductive material and contacts the lower contact plate on the lower contact seat 4 to achieve an electrically conductive connection.

[0033] In terms of selection, the second fuse 3-22 of the ejection part adopts a K-type fuse, and its selection is carried out according to existing general technical specifications. For the rated current selection of the first fuse 3-16 (current-limiting fuse) of the current-limiting part, it must meet the following three core requirements: (1) In terms of the current breaking range, when the fault current exceeds the maximum breaking capacity of the second fuse 3-22, the first fuse 3-16 must complete the breaking; conversely, when the current is lower than the minimum breaking threshold of the first fuse 3-16, the second fuse 3-22 should achieve reliable breaking.

[0034] (2) In view of the protection requirements of the distribution transformer, the first fuse 3-16 must have the following tolerance capabilities: it can withstand the transformer overload current without being damaged, and at the same time it must be able to withstand the transformer electromagnetic surge impact.

[0035] (3) From an economic perspective, when the second fuse 3-22 performs a normal breaking action, the system should avoid causing unnecessary damage to the first fuse 3-16 as much as possible to extend the service life of key components. The specific selection method uses the following two technical parameters as the basis for judgment: (1) Joule integral characteristic (I²t) matching principle: The maximum pre-arc I²t value of the K-type fuse should be less than twice the minimum pre-arc I²t value of the current-limiting fuse.

[0036] (2) Time-current characteristic (TCC) coordination requirements: The intersection of the maximum action TCC curve of the K-type fuse and the minimum pre-arc TCC curve of the current-limiting fuse must meet two conditions at the same time: the current value at the intersection must not be lower than the rated minimum breaking current of the current-limiting fuse, and must not exceed the rated maximum breaking current of the K-type fuse.

[0037] During installation, the second tube body 3-5 is removed, and the lower half of the second fuse 3-22 pre-assembled with the metal block 3-20 and the auxiliary arc-extinguishing tube 3-21 is passed through the second tube body 3-5, and then the lower end is passed around the flap 3-9, so that the first plate body is clamped on the fixing hook 3-6, and then connected to the threaded column of the rotating frame 3-7. At this time, the second fuse 3-22 is tensioned, and under the action of the second fuse 3-22 and the flap 3-9, the rotating frame 3-7 cannot rotate relative to the second tube body 3-5. The current limiting and injection components are then threaded together to form the complete fuse carrier 3. The fuse carrier 3 is then lifted using the hanging ring, and the hanging shaft 3-8 at the lower end is placed onto the mounting bracket 4-1 of the lower contact seat 4. This allows the rotating bracket 3-7 to be electrically connected to the lower contact seat 4. The upper end of the fuse carrier 3 is then pushed forward, and guided by the guide bracket 2-2, the raised portion of the upper metal seat 3-1 engages the upper contact piece 2-1, completing the electrically conductive connection. Simultaneously, the rotating pinch plate 3-2 engages the cylindrical portion at the bottom of the limiting plate 2-3. The incoming line is now electrically connected to the outgoing line via the upper contact seat 2, fuse carrier 3, and lower contact seat 4, in sequence.

[0038] When the on-site operating current is less than or equal to the rated current of the fuse, the fuse is equivalent to a low-impedance conductor, and its own heat generation is low. The heat generated is lower than the melting temperature of the internal fuse (fuse wire), and the heat is balanced with its own heat dissipation. It can operate stably for a long time and will not trigger the drop-off action.

[0039] When the on-site fault current is greater than the rated current of the fuse and less than the minimum breaking current of the first fuse 3-16, the current limiting part does not meet the breaking conditions and operates normally. At the same time, the second fuse 3-22 will quickly heat up and melt, and the generated arc will react with the internal material of the auxiliary arc extinguishing tube 3-21 to produce jet gas. At the same time, the second torsion spring pushes the flap 3-9 to rotate, and the disconnected second fuse 3-22 is pulled out, and the flap 3-9 is separated from the fixed hook 3-6. At this time, the rotating frame 3-7 will be able to rotate freely relative to the second tube body 3-5. Therefore, under the action of the weight of the fuse carrier 3, the main body of the fuse carrier 3 falls, and the rotating frame 3-7 rotates clockwise around the hanging shaft 3-8 at the lower end, and the rotating buckle plate 3-2 at the upper end automatically separates from the limit plate 2-3, causing it to fall and form a fracture.

[0040] When the expected fault current exceeds the maximum breaking current of the second fuse 3-22, the second fuse 3-22 is unable to interrupt the arc properly due to its own gas injection capability. At this point, the multi-break fuse inside the first fuse 3-16 rapidly heats up, melts, and vaporizes. The energy generated melts and crystallizes the quartz sand 3-18, forming a high-resistance crystalline layer. Simultaneously, the inductance of the spiral structure of the first fuse 3-16 limits the fault current, reducing the expected peak current. Since the first fuse 3-16 has been disconnected, the current will pass through the tensioning wire 3-13 and the steel wire 3-15, causing the low-melting-point tensioning wire 3-13 to be disconnected, and the impact column 3-11 will pop up upward under the action of the compression spring 3-12, and hit the rotating buckle plate 3-2 to overcome the force of the first torsion spring 3-4 and separate from the limit plate 2-3. Since the fuse is placed at an angle and the lower end is only connected to the hanging frame 4-1 through the hanging shaft 3-8, the entire fuse carrier 3 will rotate and fall under the action of its own weight after the upper end is tripped, completing the interruption of the fault current.

[0041] Obviously, when the expected current of the on-site fault is between the minimum breaking current of the first fuse 3-16 and the maximum breaking current of the second fuse 3-22, both parts will trigger the melting. Whether the rotating frame 3-7 is released to cause the fuse carrier 3 to fall, or the upper end is triggered to collide, it will cause the upper end to trip and complete the drop breaking.

[0042] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. The scope of the present invention is defined by the claims rather than the foregoing description.

Claims

1. A full-range drop-out fuse, comprising a base (1), wherein the upper end and the lower end of the base (1) are fixedly connected to an upper contact seat (2) and a lower contact seat (4), respectively, and a fuse carrier (3) is installed between the upper contact seat (2) and the lower contact seat (4), characterized in that: The fuse carrier (3) is of split type, comprising a current limiting part and an ejection part connected to each other in a detachable manner, wherein a first fuse (3-16) in the current limiting part and a second fuse (3-22) in the ejection part are connected in series between an upper contact seat (2) and a lower contact seat (4).

2. The full-range drop-out fuse according to claim 1, characterized in that: The detachable connection is a threaded connection.

3. The full-range drop-out fuse according to claim 1, wherein: The current limiting part and the injection part also realize the conductive connection between the first fuse (3-16) and the second fuse (3-22) through the detachable connection.

4. The full-range drop-out fuse according to claim 1, wherein: The current limiting portion comprises a first tube body (3-3), an upper metal seat (3-1) installed at the upper end of the first tube body (3-3), a lower metal seat (3-19) installed at the lower end of the first tube body (3-3), a ceramic quartz column (3-17) installed inside the first tube body (3-3), and the first fuse (3-16) wound around the outside of the ceramic quartz column (3-17); the space between the first tube body (3-3) and the ceramic quartz column (3-17) is filled with quartz sand (3-18); The upper metal seat (3-1) is used for conductive connection with the upper contact piece (2-1) in the upper contact seat (2); the upper end of the first fuse (3-16) is connected to the upper metal seat (3-1), and the lower end is connected to the lower metal seat (3-19); the lower metal seat (3-19) is used for detachably connecting with the upper end of the injection part.

5. The full-range drop-out fuse according to claim 4, characterized in that: A tripper is also installed at the upper end of the current limiting part; the tripper comprises a rotating buckle plate (3-2) buckled with the bottom end of the limiting plate (2-3) of the upper contact seat (2) and a striker installed in the upper metal seat (3-1) for striking the rotating buckle plate (3-2).

6. The full-range drop-out fuse according to claim 5, wherein: The rotating buckle plate (3-2) is mounted on the upper metal seat (3-1) by a rotating connection. A first torsion spring (3-4) is also mounted on the upper metal seat (3-1). The first torsion spring (3-4) is used to push the rotating buckle plate (3-2) so that its left end maintains contact with the upper limit plate (2-3).

7. The full-range drop-out fuse according to claim 5, wherein: The striker comprises a metal shell (3-10) installed in an upper metal seat (3-1), a striker column (3-11) installed in the metal shell (3-10), a compression spring (3-12) installed in the metal shell (3-10) for pushing the striker column (3-11) upward, and a tensioning wire (3-13) whose upper end is connected to the lower end of the striker column (3-11) and whose lower end is fixedly connected to an insulating block (3-14) in an inner hole of a ceramic quartz column (3-17); the tensioning wire (3-13) is connected in parallel with a first fuse (3-16) between the upper metal seat (3-1) and the lower metal seat (3-19).

8. The full-range drop-out fuse according to claim 7, wherein: The impact column (3-11) is made of a conductive material and is in contact with the metal shell (3-10), thereby achieving a conductive connection with the upper metal seat (3-1); The lower end of the tensioning wire (3-13) is also electrically connected to the lower metal seat (3-19) via a steel wire (3-15) arranged in the inner hole of the ceramic quartz column (3-17).

9. The full-range drop-out fuse according to claim 4, wherein: The injection portion comprises a second tube body (3-5), the second tube body (3-5) is made of a conductive material, and the upper end is threadedly connected to the lower metal seat (3-19); A countersunk hole is provided at the upper end of the inner hole of the second tube body (3-5), a metal block (3-20) is provided in the countersunk hole, the upper end of the second fuse (3-22) passes through the auxiliary arc-extinguishing tube (3-21) and is connected to the metal block (3-20), thereby achieving an electrically conductive connection with the second tube body, and the lower end extends from the lower end of the second tube body (3-5).

10. The full-range drop-out fuse according to claim 9, wherein: A rotating frame (3-7) is mounted on the outer side of the lower end of the second tube body (3-5) by a rotating connection, and a hanging shaft (3-8) is provided on the rotating frame (3-7), and the hanging shaft (3-8) cooperates with the hanging frame (4-1) on the lower contact seat (4); A fixing hook (3-6) is also provided on the outer side of the lower end of the second tube (3-5); a flap (3-9) is also mounted on the rotating frame (3-7) in a rotating connection manner, and the flap (3-9) is L-shaped; the lower end of the second fuse (3-22) passes around the second plate of the flap (3-9), so that the end of the first plate of the flap (3-9) is hooked to the fixing hook (3-6), and then is connected to the rotating frame (3-7) through a stud to achieve conductive fixing connection; a second torsion spring for pushing the flap (3-9) to separate the first plate from the fixing hook (3-6) is also mounted on the rotating frame (3-7); The rotating frame (3-7) is made of conductive material and contacts the lower contact piece on the lower contact seat (4) to achieve conductive connection.

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