Telescopic LTD secondary transmission line inner cylinder and implementation method

Abstract

The invention relates to a telescopic LTD secondary transmission line inner cylinder and an implementation method, and solves the technical problems that an existing LTD pulse source is large in physical size and cannot meet experimental requirements. The device comprises an outer cylinder, a middle cylinder, a bottom cylinder and a telescopic electric cylinder, the outer cylinder, the middle cylinder and the bottom cylinder are respectively matched with the impedance of the LTD module step by step; the middle cylinder is slidably and coaxially sleeved on the bottom cylinder, and the outer cylinder is slidably and coaxially sleeved on the middle cylinder to jointly form a secondary transmission line inner cylinder; the telescopic electric cylinder is arranged in the outer cylinder, the middle cylinder and the bottom cylinder and connected with the bottom cylinder and the outer cylinder. A bottom cylinder limiting assembly is arranged at the front end part of the bottom cylinder; a middle cylinder limiting assembly is arranged at the front end part of the middle cylinder, and a middle cylinder sealing assembly is arranged on the inner wall of the rear end; an outer cylinder sealing assembly is arranged on the inner wall of the rear end of the outer cylinder; each of the middle cylinder sealing assembly and the outer cylinder sealing assembly comprises a sealing boss, a Y-shaped sealing ring, an inflatable sealing ring, a positioning ring and a conductive contact spring; and the inflatable sealing ring is communicated with an external air pump.

Description

Technical Field

[0001] The present invention relates to a transmission line, in particular to a retractable LTD secondary transmission line inner cylinder and an implementation method thereof. Background Art

[0002] As a pulsed power source capable of generating high voltage, high current, and short pulses, the fast-pulse linear transformer driver (LTD) has attracted widespread attention from researchers due to its enormous potential and technological advantages in high-current driver sources for Z-pinch inertial confinement fusion and compact high-voltage driver sources for flash photography. To further increase the output voltage and power of LTDs, multiple modules are typically connected in series to form a single LTD pulse source, with power reaching hundreds of GW to several terawatts.

[0003] A single-channel LTD pulse source consists of a primary and secondary circuit. The secondary circuit requires a long metal inner tube that runs through each LTD module. This inner tube, along with the electrodes within the LTD module cavity, forms the secondary transmission line. The multiple LTD modules act as the primary of a pulse transformer, discharging sequentially according to a specific timing sequence, inducing high-voltage pulses on the inner tube of the secondary transmission line. Depending on the wave impedance characteristics and application requirements, the secondary transmission line typically uses deionized water, transformer oil, SF6 gas, or a vacuum as the insulating medium. The secondary transmission line inner tube is a key component of the LTD, significantly impacting the superposition of electrical pulses and power transmission in the multi-stage series LTD circuit.

[0004] The inner barrel of the secondary transmission line of an existing single-channel LTD pulse source is typically composed of several cylindrical sections welded or screwed together. After fabrication and installation, the axial length of the inner barrel cannot be adjusted. Therefore, the inner barrel length must be at least greater than the sum of the axial lengths of multiple LTD modules in series. For a single-channel LTD pulse source composed of dozens of modules in series, the inner barrel length can reach several meters or even tens of meters. For example, the single-channel LTD prototype for the Z-pinch fusion device developed by the China Academy of Engineering Physics consists of 50 modules in series. Including the extended section at the end of the LTD, the entire inner barrel length exceeds 20 meters. The inner barrel has a diameter of approximately 1.2 meters at its thickest point and 1.08 meters at its thinnest point, weighing several tons. For a single-channel LTD pulse source, when installing the inner tube of the secondary transmission line, it is usually pushed in from the front of the pulse source head end and passed through each level of modules in sequence; when repairing the modules of each level of the LTD pulse source, it is necessary to first pull the inner tube out completely from the pulse source and use a gantry to lift out the LTD module to be repaired. This requires that a space at least equal to the length of the inner tube be reserved in front of the pulse source head end, which increases the floor space occupied by the LTD pulse source and reduces the efficiency of space utilization.

[0005] Chinese patent CN103138035A discloses a rigid coaxial pulse transmission line with online adjustable length, in which both the inner and outer conductors are constructed as a multi-layer nested structure. The inner conductor consists of two tightly fitted thin-walled tubes; the outer conductor adopts a three-layer nested structure, with the inner and outer layers fixed relative to each other, and the middle layer capable of varying its axial position to adjust the outer conductor's length. The outer layer forms two cavities with the middle and inner layers, respectively. The cavity between the outer and middle layers communicates with the insulating medium cavity between the inner and outer conductors of the transmission line, while the cavity between the outer and inner layers communicates with the outside world. As the transmission line length changes, the space between the inner and outer conductors remains filled with insulating medium. However, this structure has poor insulation sealing and is primarily designed for online adjustment of pulse transmission lines, making it unsuitable for use with LTD pulse sources. This structure requires the inner and outer conductors to change length simultaneously to achieve expansion and contraction, while LTD pulse sources are bulky and cannot be arbitrarily adjusted in the size of the outer tube, which is used to generate pulse waves. Furthermore, LTD pulse sources have strict sealing requirements, and this structure cannot guarantee sealing performance. Summary of the Invention

[0006] The purpose of the present invention is to solve the technical problem that the existing LTD pulse source has a large physical volume and cannot meet the experimental requirements, and to provide a retractable LTD secondary transmission line inner cylinder and an implementation method.

[0007] The concept of the present invention is as follows: the inner cylinder of the secondary transmission line is composed of multiple coaxially nested cylindrical electrodes. A Y-shaped sealing structure is used between the cylindrical electrodes to prevent leakage of the insulating medium (deionized water, transformer oil, propylene carbonate, SF6 gas, vacuum, etc.) in the secondary transmission line. Built-in copper sleeve bearings are used to ensure the coaxiality between the cylindrical electrodes, and inflatable sealing rings are used to fine-tune the posture of each cylindrical electrode segment. Multi-stage telescopic electric cylinders are used to drive each cylindrical electrode segment to extend or retract along the axis.

[0008] In order to achieve the above objectives and complete the above concepts, the technical solutions provided by the present invention are as follows:

[0009] A retractable LTD secondary transmission line inner cylinder, which is special in that:

[0010] It includes an outer cylinder, at least one middle cylinder, a bottom cylinder and a telescopic electric cylinder;

[0011] Definition: The tail end direction of the bottom barrel is the rear end direction;

[0012] The outer diameter of the outer tube gradually decreases from the front to the rear end, and the wave impedance gradually increases. The wave impedance of the middle tube and the bottom tube remains unchanged from the front to the rear end, which is used to match the impedance of the LTD module step by step.

[0013] The rear end of the middle tube can be slidably and coaxially sleeved on the front end of the bottom tube, and the rear end of the outer tube can be slidably and coaxially sleeved on the front end of the middle tube. Alternatively, multiple middle tubes can be coaxially sleeved in sequence to form a middle tube assembly, and the rear end of the middle tube assembly can be slidably and coaxially sleeved on the front end of the bottom tube, and the rear end of the outer tube can be slidably and coaxially sleeved on the front end of the middle tube assembly; the outer tube, the middle tube, and the bottom tube together constitute the inner tube of the secondary transmission line;

[0014] A positioning slot is provided at the center of the inner wall at the rear end of the bottom tube. The telescopic electric cylinder is arranged inside the outer tube, the middle tube and the bottom tube. Its driving end is engaged with the positioning slot of the bottom tube, and its fixed end is connected to the front end of the outer tube.

[0015] The front end of the bottom tube is provided with a bottom tube limiting assembly; the front end of the middle tube is provided with a middle tube limiting assembly, and the rear end inner wall is provided with a middle tube sealing assembly; the rear end inner wall of the outer tube is provided with an outer tube sealing assembly;

[0016] Both the middle tube sealing assembly and the outer tube sealing assembly include a sealing boss extending inward, and a Y-shaped sealing ring, an inflatable sealing ring and a positioning ring arranged on the sealing boss in sequence from the front end to the rear end; the inflatable sealing ring is connected to the external air pump; the lip of the Y-shaped sealing ring faces the rear end, and it is connected to the positioning ring by at least three positioning pins.

[0017] Furthermore, copper sleeve bearings are provided between the outer cylinder, the middle cylinder and the bottom cylinder to ensure that the coaxiality between them is within ±1mm.

[0018] Furthermore, there is one in the middle barrel.

[0019] Furthermore, the Y-shaped sealing ring, the inflatable sealing ring and the positioning ring are all located at the front end of the sealing boss.

[0020] Furthermore, an O-ring is provided at the rear end of the sealing boss.

[0021] Furthermore, the middle cylinder and the bottom cylinder are straight cylinders.

[0022] Furthermore, the bottom tube limiting assembly is a bottom tube convex ring provided on the outer periphery of the front end of the bottom tube and extending outward, and the outer diameter of the bottom tube convex ring is adapted to the inner diameter of the front end of the middle tube;

[0023] The middle cylinder limiting assembly is a middle cylinder convex ring arranged on the outer periphery of the front end of the middle cylinder and extending outward, and the outer diameter of the middle cylinder convex ring is adapted to the inner diameter of the front end of the outer cylinder.

[0024] Furthermore, it also includes a conductive contact spring, which is located at the rear end of the sealing boss, and an O-ring is located between the conductive contact spring and the inflatable sealing ring;

[0025] Furthermore, the interior of the inflatable sealing ring is filled with nitrogen;

[0026] The conductive contact spring is a beveled coil beryllium copper contact spring;

[0027] The outer cylinder, middle cylinder and bottom cylinder electrodes are all made of stainless steel.

[0028] The present invention also provides a method for realizing the above-mentioned retractable LTD secondary transmission line inner barrel, which is special in that it includes the following steps:

[0029] S, when the inner tube of the LTD secondary transmission line needs to be extended

[0030] S1, extracting the internal gas of the inflatable sealing ring;

[0031] S2, moves the middle cylinder and bottom cylinder by telescopic electric cylinder, so that the inner cylinder of LTD secondary transmission line is extended into place;

[0032] S3, the telescopic electric cylinder is disconnected from the positioning slot of the bottom cylinder and retracted;

[0033] S4: Inflate the inflatable seal ring with internal gas and adjust the posture of the middle tube. At this point, the inflatable seal ring and the Y-shaped seal ring form a double seal, and the inner tube of the LTD secondary transmission line is stretched, meeting the working requirements of electric pulse superposition and power transmission.

[0034] R, when the inner tube of the LTD secondary transmission line needs to be contracted

[0035] R1, extracts the internal gas of the inflatable sealing ring;

[0036] R2, the telescopic cylinder extends and connects with the positioning slot of the bottom cylinder;

[0037] R3, the middle and bottom cylinders are moved by telescopic electric cylinders, so that the inner cylinder of the LTD secondary transmission line is retracted into place; at this point, the inner cylinder of the LTD secondary transmission line is completely retracted, meeting the physical space requirements for installation and maintenance.

[0038] The present invention has the following beneficial effects compared with the prior art:

[0039] 1. The present invention provides a retractable LTD secondary transmission line inner cylinder, which forms the secondary transmission line inner cavity through a three-section coaxial nested structure, and realizes electric axial extension or contraction through a telescopic electric cylinder; the coaxiality of each section is ensured by a copper sleeve bearing to ensure the smoothness of the extension and contraction; the posture fine-tuning and double sealing are achieved through a Y-shaped sealing ring and an inflatable sealing ring, and the electrical contact resistance is reduced by a beveled beryllium copper contact spring, which reduces the probability of sparking due to poor contact and improves transmission efficiency and stability. In combination with the above structure, the present invention can achieve a reduction in physical volume while meeting the sealing performance required by the experiment, and has important application prospects in high-voltage and high-current pulse power devices such as fast pulse linear transformer drive sources, induction voltage superimposers, and impedance matching Marx generators.

[0040] 2. This invention provides a method for implementing a retractable inner cylinder for an LTD secondary transmission line. This design addresses the challenges of large axial length and inefficient space utilization in the inner cylinder of a secondary transmission line with LTD pulse sources connected in series with multiple modules. During LTD operation, the inner cylinder extends to its longest position, enabling multi-module electrical pulse superposition and power transmission. During LTD installation or maintenance, the inner cylinder retracts to its shortest position, reducing axial length and occupied physical space. This improves the maintainability of large-scale LTD installations and promotes the engineering application of LTD technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the extended structure of a retractable LTD secondary transmission line inner cylinder embodiment of the present invention;

[0042] Figure 2 is a schematic diagram of a contraction structure of an embodiment of the present invention;

[0043] Figure 3 1 is a schematic structural diagram of the middle tube in an embodiment of the present invention;

[0044] Figure 4 yes Figure 3 -A magnified schematic diagram of B;

[0045] Figure 5 yes Figure 3 -Enlarged schematic diagram of C.

[0046] Figure Number:

[0047] 1-outer cylinder; 2-middle cylinder; 3-bottom cylinder; 4-telescopic cylinder;

[0048] 5-Y-type sealing ring; 6-inflatable sealing ring; 7-locating ring; 8-locating pin; 9-O-type sealing ring; 10-conductive contact spring. DETAILED DESCRIPTION

[0049] The specific technical solutions in the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0050] This invention addresses the challenges of large axial length and low space efficiency in the inner cylinder of a secondary transmission line for a multi-stage modular LTD pulse source. By doing so, the invention proposes a retractable inner cylinder for an LTD secondary transmission line. The inner cylinder consists of several coaxially nested cylindrical electrodes (outer, middle, and bottom). A Y-shaped seal is used between the segments to prevent leakage of the insulating medium (deionized water, transformer oil, propylene carbonate, SF6 gas, vacuum, etc.) within the secondary transmission line. Inflatable seals are used to fine-tune the cylinder's posture. Coaxiality between the segments is achieved using built-in copper bearings (not shown). Multi-stage telescopic electric cylinders are used to drive the segments to extend and retract along their axis. During LTD operation, the cylinders extend to their longest position, ensuring pulse superposition and power transmission. During LTD installation and maintenance, the cylinders retract to their shortest position, minimizing physical space occupation.

[0051] Based on the above structure, an embodiment of the present invention designs a retractable LTD secondary transmission line inner cylinder. The LTD pulse source is composed of 10 modules connected in series, and the secondary transmission line inner cylinder consists of three sections: the outer cylinder, the middle cylinder, and the bottom cylinder. The secondary transmission line composed of the inner cylinder and the inner cavity of the LTD module uses deionized water as the insulating medium. The outer cylinder is fixed on the support platform, and the middle cylinder and the bottom cylinder can slide along the axis. The outer cylinder adopts a conical structure, and the transmission line wave impedance increases linearly along the power transmission direction, and is matched step by step with the impedance of several levels of LTD modules in the first section; the middle cylinder and the bottom cylinder are straight cylinders, and the transmission line wave impedance remains constant along the power transmission direction, and the impedance is matched with the impedance of the LTD module corresponding to its middle position. Copper bearings are used between the three to ensure the cylinders' coaxiality within ±1mm. An inflatable seal ring, a Y-shaped seal ring, and a conductive contact spring (beryllium copper spring) are placed inside the outer and middle cylinders, respectively. The seal rings are filled with nitrogen, and the gas is released when the cylinders need to be extended or retracted. Once the inner cylinder is extended, the seal rings are filled with nitrogen at a certain pressure, which not only fine-tunes the cylinder's posture but also acts as a double seal. The Y-shaped seal ring isolates the insulating medium within the secondary transmission line. The conductive contact spring reduces the electrical contact resistance between adjacent cylinders, minimizing the probability of sparks due to poor contact.

[0052] Figure 1-Figure 3 A retractable LTD secondary transmission line inner cylinder is provided in an embodiment of the present invention. Figure 4 、 Figure 5 This is an enlarged schematic diagram, including an outer cylinder 1, a middle cylinder 2, a bottom cylinder 3 and a telescopic electric cylinder 4.

[0053] Definition: The tail end direction of the bottom tube 3 is the rear end direction.

[0054] The outer tube 1 is conical, while the middle tube 2 and bottom tube 3 are straight cylinders. The outer diameter of the outer tube 1 decreases linearly from front to back, while the wave impedance gradually increases, ensuring that the wave impedance of the secondary transmission line matches the impedance of the several LTD modules in the first stage. The wave impedance of the middle tube 2 and bottom tube 3 remains constant from front to back, and the outer diameter remains constant, facilitating expansion and contraction and sliding.

[0055] The rear end of the middle tube 2 can be slidably and coaxially sleeved on the front end of the bottom tube 3, and the rear end of the outer tube 1 can be slidably and coaxially sleeved on the front end of the middle tube 2; the outer tube 1, the middle tube 2, and the bottom tube 3 are nested along the same axis to form the inner tube of the secondary transmission line.

[0056] A positioning slot is provided in the center of the inner wall at the rear end of the bottom tube 3. The telescopic electric cylinder 4 is arranged inside the outer tube 1, the middle tube 2 and the bottom tube 3. Its driving end is engaged with the positioning slot of the bottom tube 3, and the fixed end is connected to the front end of the outer tube 1.

[0057] The front end of the bottom tube 3 is provided with a bottom tube limiting assembly; the front end of the middle tube 2 is provided with a middle tube limiting assembly, and the rear end inner wall is provided with a middle tube sealing assembly; the rear end inner wall of the outer tube 1 is provided with an outer tube sealing assembly; the bottom tube limiting assembly is a bottom tube convex ring arranged on the outer periphery of the front end of the bottom tube 3 and facing outward, and the outer diameter of the bottom tube convex ring is adapted to the front end inner diameter of the middle tube 2; the middle tube limiting assembly is a middle tube convex ring arranged on the outer periphery of the front end of the middle tube 2 and facing outward, and the outer diameter of the middle tube convex ring is adapted to the front end inner diameter of the outer tube 1.

[0058] Both the middle and outer cylinder seal assemblies include an inward-extending sealing boss. Positioned at the front of the boss are, from front to back, a Y-ring 5, an inflatable seal ring 6, and a retaining ring 7. At the rear of the boss, an O-ring 9 and a conductive contact spring 10 are located. The inflatable seal ring 6 is connected to an external air pump. The lip of the Y-ring 5 faces the rear end and is connected to the retaining ring 7 via three locating pins 8. This structure ensures the tightness of the insulating medium within the secondary transmission line, with the Y-ring providing the primary sealing function and the inflatable seal ring used to fine-tune the posture of each cylinder segment. The bottom and middle cylinder limiter assemblies share the same structure, while the middle and outer cylinder seal assemblies share the same structure.

[0059] Copper sleeve bearings are also provided between the outer tube 1, the middle tube 2 and the bottom tube 3 to ensure the coaxiality between them is within ±1mm. The copper sleeve bearings are arranged on the inner wall of the sealing boss, between the positioning ring 7 and the O-ring 9.

[0060] In the embodiment of the present invention, the interior of the inflatable sealing ring 6 is filled with nitrogen; the conductive contact spring 10 is a beveled beryllium copper contact spring; and the electrode materials of the outer tube 1, the middle tube 2 and the bottom tube 3 are all stainless steel.

[0061] The working principle of the present invention is as follows:

[0062] When LTD is working, the multi-stage telescopic electric cylinder drives each section of the cylindrical electrode to stretch to the longest position along the axis, forming a complete secondary transmission line inner cylinder for multi-stage module electric pulse superposition and power transmission.

[0063] When the LTD module needs to be installed or repaired, the multi-stage telescopic electric cylinder drives each section of the cylindrical electrode to retract along the axis to the shortest position, reducing the physical space occupied and making it easier for operators to carry out maintenance work.

[0064] The steps of the embodiment of the present invention are as follows:

[0065] Prepare the inner cylinder of the LTD secondary transmission line;

[0066] S, when the inner tube of the LTD secondary transmission line needs to be extended

[0067] S1, extracting the internal gas of the inflatable sealing ring 6;

[0068] S2, the middle cylinder 2 and the bottom cylinder 3 are moved by the telescopic electric cylinder 4, so that the inner cylinder of the LTD secondary transmission line is extended into place;

[0069] S3, the telescopic cylinder 4 is disconnected from the positioning slot of the bottom cylinder 3 and retracted;

[0070] S4: Inflate the inflatable seal ring 6 with internal gas and fine-tune the posture of the middle tube 2. At this point, the inflatable seal ring 6 and the Y-shaped seal ring 5 form a double seal, and the inner tube of the LTD secondary transmission line is stretched, meeting the working requirements of electric pulse superposition and power transmission.

[0071] R, when the inner tube of the LTD secondary transmission line needs to be contracted

[0072] R1, extract the internal gas of the inflatable sealing ring 6;

[0073] R2, the telescopic cylinder 4 extends and connects with the positioning slot of the bottom cylinder 3;

[0074] R3, the middle tube 2 and the bottom tube 3 are moved by the telescopic electric cylinder 4, so that the inner tube of the LTD secondary transmission line is retracted into place; at this point, the inner tube of the LTD secondary transmission line is completely retracted, meeting the physical space requirements for installation and maintenance.

[0075] The implementation effects of the embodiments of the present invention are as follows:

[0076] When the inner tube is extended to its maximum position, its axial length is approximately 2.7 m, and when it is retracted to its minimum position, its axial length is approximately 1.3 m, which is reduced by half.

[0077] The above content is only one embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent transformation made using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A retractable LTD secondary transmission line inner barrel, characterized by: It comprises an outer cylinder (1), at least one middle cylinder (2), a bottom cylinder (3) and a telescopic electric cylinder (4); Definition: The tail end direction of the bottom tube (3) is the rear end direction; The outer diameter of the outer cylinder (1) gradually decreases from the front end to the rear end, and the wave impedance gradually increases; the wave impedance of the middle cylinder (2) and the bottom cylinder (3) remains unchanged from the front end to the rear end, and are used to perform step-by-step matching with the impedance of the LTD module respectively; The rear end of the middle tube (2) can be slidably and coaxially sleeved on the front end of the bottom tube (3), and the rear end of the outer tube (1) can be slidably and coaxially sleeved on the front end of the middle tube (2); or, a plurality of middle tubes (2) can be coaxially sleeved in sequence to form a middle tube assembly, and the rear end of the middle tube assembly can be slidably and coaxially sleeved on the front end of the bottom tube (3), and the rear end of the outer tube (1) can be slidably and coaxially sleeved on the front end of the middle tube assembly; the outer tube (1), the middle tube (2), and the bottom tube (3) together constitute the inner tube of the secondary transmission line; A positioning slot is provided at the center of the inner wall of the rear end of the bottom cylinder (3); the telescopic electric cylinder (4) is arranged inside the outer cylinder (1), the middle cylinder (2) and the bottom cylinder (3); its driving end is engaged with the positioning slot of the bottom cylinder (3), and its fixed end is connected to the front end of the outer cylinder (1); The front end of the bottom cylinder (3) is provided with a bottom cylinder limiting assembly; the front end of the middle cylinder (2) is provided with a middle cylinder limiting assembly, and the rear end inner wall is provided with a middle cylinder sealing assembly; the rear end inner wall of the outer cylinder (1) is provided with an outer cylinder sealing assembly; The middle cylinder sealing assembly and the outer cylinder sealing assembly both comprise an inwardly extending sealing boss, a Y-shaped sealing ring (5), an inflatable sealing ring (6) and a positioning ring (7) arranged on the sealing boss in sequence from the front end to the rear end; the inflatable sealing ring (6) is connected to an external air pump; the lip of the Y-shaped sealing ring (5) faces the rear end, and is connected to the positioning ring (7) via at least three positioning pins (8).

2. The retractable LTD secondary transmission line inner barrel according to claim 1, characterized in that: Copper sleeve bearings are also provided between the outer cylinder (1), the middle cylinder (2) and the bottom cylinder (3) to ensure that the coaxiality between the two is within ±1 mm.

3. The retractable LTD secondary transmission line inner barrel according to claim 2, characterized in that: The middle tube (2) has one.

4. A retractable LTD secondary transmission line inner barrel according to any one of claims 1 to 3, characterized in that: The Y-shaped sealing ring (5), the inflatable sealing ring (6) and the positioning ring (7) are all located at the front end of the sealing boss.

5. The retractable LTD secondary transmission line inner barrel according to claim 4, characterized in that: An O-type sealing ring (9) is also provided at the rear end of the sealing boss.

6. The retractable LTD secondary transmission line inner barrel according to claim 5, characterized in that: The middle cylinder (2) and the bottom cylinder (3) are straight cylinders.

7. The retractable LTD secondary transmission line inner barrel according to claim 6, characterized in that: The bottom tube limiting assembly is a bottom tube convex ring arranged on the outer periphery of the front end of the bottom tube (3) and extending outward, and the outer diameter of the bottom tube convex ring is adapted to the inner diameter of the front end of the middle tube (2); The middle cylinder limiting assembly is a middle cylinder convex ring arranged on the outer periphery of the front end of the middle cylinder (2) and extending outward, and the outer diameter of the middle cylinder convex ring is adapted to the inner diameter of the front end of the outer cylinder (1).

8. The retractable LTD secondary transmission line inner barrel according to claim 7, characterized in that: It also includes a conductive contact spring (10), which is located at the rear end of the sealing boss, and an O-type sealing ring (9) is located between the conductive contact spring (10) and the inflatable sealing ring (6).

9. The retractable LTD secondary transmission line inner barrel according to claim 8, characterized in that: The interior of the inflatable sealing ring (6) is filled with nitrogen; The conductive contact spring (10) is a beveled coil beryllium copper contact spring; The electrodes of the outer cylinder (1), the middle cylinder (2) and the bottom cylinder (3) are all made of stainless steel.

10. A method for realizing the retractable LTD secondary transmission line inner tube according to any one of claims 1 to 9, characterized in that: The steps are as follows: S, when the inner tube of the LTD secondary transmission line needs to be extended S1, extracting the internal gas of the inflatable sealing ring (6); S2, the middle cylinder (2) and the bottom cylinder (3) are moved by the telescopic electric cylinder (4), so that the inner cylinder of the LTD secondary transmission line is extended into place; S3, the telescopic electric cylinder (4) is disconnected from the positioning slot of the bottom cylinder (3) and retracted; S4, fill the inflatable sealing ring (6) with internal gas and adjust the posture of the middle cylinder (2); at this time, the inflatable sealing ring (6) and the Y-shaped sealing ring (5) form a double seal, and the inner cylinder of the LTD secondary transmission line is stretched to meet the working requirements of electric pulse superposition and power transmission; R, when the inner tube of the LTD secondary transmission line needs to be contracted R1, extracting the internal gas of the inflatable sealing ring (6); R2, the telescopic electric cylinder (4) extends and connects with the positioning slot of the bottom cylinder (3); R3, by moving the middle tube (2) and the bottom tube (3) through the telescopic electric cylinder (4), the inner tube of the LTD secondary transmission line is retracted into place; at this time, the inner tube of the LTD secondary transmission line is completely retracted, meeting the physical space requirements for installation and maintenance.

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