A gas-insulated switchgear underpressure trip protection device

Abstract

This utility model relates to a gas-insulated switchgear undervoltage trip protection device, belonging to the technical field of gas-insulated switchgear undervoltage trip protection devices. It is installed on any fixed plane of the operating mechanism of the gas-insulated switchgear circuit breaker, including a drive mechanism and a transmission mechanism. The drive mechanism is a bistable permanent magnet locking electromagnetic drive mechanism that maintains closing under power failure and instantaneously excites and trips under voltage failure. It is housed in a sealed chamber of a fully sealed, isolated mounting base, with the base achieving leakage-free power output through a bellows dynamic sealing assembly. The transmission mechanism is a single-full-point force amplification lever. The short end of the lever's power arm forms a sliding hinge connection with the bellows transmission push rod. The end of the lever's resistance arm is equipped with an arc-shaped trigger head that directly abuts against the trigger plane of the circuit breaker's tripping half-shaft to achieve impact-free tripping triggering. This utility model overcomes the shortcomings of traditional gas-insulated switchgear undervoltage trip devices, such as coil burnout due to prolonged energization, high sealing leakage rate, large transmission rigidity impact, and poor adaptability.

Description

Technical Field

[0001] This application relates to the technical field of gas-insulated switchgear protection devices, and in particular to a gas-insulated switchgear underpressure trip protection device. Background Technology

[0002] Gas-insulated switchgear undervoltage trip protection devices are safety protection devices installed on gas-insulated metal-enclosed switchgear. They are divided into two categories: electrical undervoltage and gas undervoltage. Electrical undervoltage devices trigger circuit breaker tripping when the power supply voltage drops suddenly or disappears, preventing the equipment from accidentally restarting after the voltage is restored, thus ensuring personal and equipment safety. Gas undervoltage devices operate when the pressure of insulating gases such as SF6 is lower than the threshold, cutting off the circuit and preventing electrical faults caused by a decline in insulation performance.

[0003] Currently, gas-insulated switchgear circuit breakers are generally equipped with undervoltage release devices to trigger the circuit breaker to trip when the secondary circuit loses power, thus preventing the main circuit fault from escalating due to protection device failure. However, existing conventional undervoltage release devices still have many shortcomings that urgently need to be addressed:

[0004] First, the single-coil long-term energized holding method is adopted, which causes the coil to heat up continuously and accelerates the aging of the winding insulation. Conventional products will experience coil burnout failure in 3-5 years, which is seriously inconsistent with the 20-year maintenance-free design life of the gas-filled switchgear. In addition, the long-term high power consumption increases the burden on the secondary power supply.

[0005] Secondly, the mechanism is directly exposed to the SF6 gas chamber environment of the gas holder. Gas decomposition products and condensation can easily corrode transmission components. In low-temperature environments, the solidification of grease can cause a sharp increase in transmission resistance, which can easily lead to core jamming and tripping failure.

[0006] Furthermore, the tripping force is designed to be fixed, which cannot adapt to fluctuations in operating resistance caused by low temperature and SF6 gas pressure leakage. This often results in insufficient tripping force and failure to operate, leading to insufficient reliability of the core protection function.

[0007] The aforementioned problems prevent the existing undervoltage release device from reliably achieving the core objective of reliably tripping the circuit breaker during secondary power failures, posing a significant safety hazard.

[0008] Therefore, it is necessary to propose a gas-insulated switchgear underpressure trip protection device to solve the above problems. Utility Model Content

[0009] This application provides a gas-insulated switchgear undervoltage trip protection device to improve upon the undervoltage tripping device configured in the gas-insulated switchgear circuit breaker in the related technology, which is used to trip the circuit when the secondary circuit loses power to avoid the expansion of the main circuit fault. However, the existing device has obvious defects: the single coil is prone to burnout when energized for a long time, the mechanism is prone to jamming and failure when exposed to the SF6 gas chamber, the tripping force is fixed and cannot adapt to the fluctuation of the operating conditions and is prone to failure to operate, and it cannot stably achieve reliable tripping, which poses a major safety hazard.

[0010] This application provides a gas-insulated switchgear undervoltage trip protection device, which is installed on any fixable plane of the gas-insulated switchgear circuit breaker operating mechanism. It is used to trigger the circuit breaker to trip when the secondary circuit loses power or the voltage falls below a set threshold. The device includes a drive mechanism and a transmission mechanism.

[0011] The drive mechanism is a bistable permanent magnet locking electromagnetic drive mechanism that maintains closing when power is lost and opens when voltage is lost. In the sealed chamber of the fully sealed and isolated mounting base, the base achieves leakage-free power output through a bellows dynamic sealing assembly.

[0012] The transmission mechanism is a single-fulcrum force amplification lever. The short end of the lever power arm is connected to the bellows transmission push rod in a sliding hinge transmission connection. The end of the lever resistance arm is provided with an arc-shaped trigger head, which directly abuts against the trigger plane of the circuit breaker tripping half shaft to achieve impact-free tripping triggering.

[0013] The technical solutions described in this application embodiment have at least the following technical effects: This device integrates a bistable permanent magnet excitation-free drive, a fully sealed bellows dynamic seal, and a lever-based, force-saving, impact-free transmission into a single structure, overcoming the drawbacks of traditional gas-insulated switchgear underpressure tripping devices, such as coil burnout due to prolonged energization, high seal leakage rate, large transmission rigidity impact, and poor adaptability. It achieves steady-state zero-power standby by relying on a permanent magnet bistable state, ensures leak-free operation of the SF6 gas chamber through bellows sealing, and balances tripping reliability and mechanism protection through lever force amplification and arc-shaped flexible triggering.

[0014] In this embodiment, the bistable permanent magnet locking electromagnetic drive mechanism includes an outer magnetic yoke, an axially magnetized annular permanent magnet, an upper stationary iron core, a lower stationary iron core, a moving iron core assembly, and an instantaneous excitation coil. The annular permanent magnet is axially clamped between the upper and lower stationary iron cores and press-fitted into the inner cavity of the outer magnetic yoke to form a closed magnetic circuit. The moving iron core assembly is coaxially installed in the central guide hole of the upper and lower stationary iron cores, and its lower end of the central push rod is coaxially adaptively connected to the bellows drive push rod through a spherical hinge. The instantaneous excitation coil is wound around the inner cavity of the outer magnetic yoke outside the annular permanent magnet, and the wiring terminal is led out from the sealed housing through an IP68-level sealed aviation plug to access the secondary control circuit.

[0015] This technical solution overcomes the shortcomings of traditional electromagnetic mechanisms, such as large magnetic leakage, poor coaxiality, susceptibility to environmental corrosion, and easy generation of lateral forces during transmission, through an integrated design of a closed magnetic circuit yoke layout, axially magnetized permanent magnet configuration, coaxial guiding motion structure, spherical adaptive hinge, and high-grade sealed lead wire structure. The closed magnetic circuit enhances the permanent magnet holding force and excitation response speed; the dual-core coaxial guidance ensures smooth and reliable mechanism operation; the spherical hinge eliminates transmission interference; and the IP68 sealed lead wire is suitable for the sealed conditions of SF6 gas-insulated switchgear.

[0016] In this embodiment, the bellows dynamic sealing assembly is pre-compressed quantitatively by a spacer sleeve during assembly, so that the bellows always maintains a pre-compression elastic force that is completely coaxial with the direction of the tripping drive spring thrust when the circuit is closed and locked.

[0017] When the secondary circuit loses voltage, a reverse pulse current is applied to the instantaneous excitation coil to counteract the permanent magnet holding force. The moving iron core is simultaneously driven by the main thrust of the tripping drive spring, the auxiliary spring force of the bellows, and its own gravity in a triple coaxial manner. The resultant force is without component loss along the axis of the moving iron core, and the tripping action is completed quickly.

[0018] This technical solution defines the initial working state of the bellows by quantitative pre-compression of the fixed-distance sleeve, constructs a multi-component coaxial force system, and utilizes the dual properties of the bellows as both a seal and an auxiliary energy storage drive. Combined with a triple coaxial force drive mode, it solves the problems of uncontrollable pre-tightening amount, large force eccentricity loss, sluggish triggering due to single power source, and easy failure of the bellows due to off-center load in traditional pressure loss tripping devices.

[0019] In this embodiment, a horizontal through groove perpendicular to the direction of push rod movement is provided on the output shaft of the bellows drive push rod. The lever fulcrum is located on the extension line of the output shaft of the bellows drive push rod. The short end of the lever power arm is slidably set in the horizontal through groove through a cylindrical pin, realizing the seamless conversion of linear motion to circular motion, and no lateral force is applied to the bellows during the transmission process.

[0020] This technical solution, through an integrated design of horizontal through-groove, coaxial support, and cylindrical pin sliding fit, solves the drawbacks of traditional transmission structures, such as backlash during motion conversion, easy generation of lateral forces, easy damage to bellows, and large power transmission losses. It achieves backlash-free and lossless conversion between linear and circular motion, ensuring accurate transmission of tripping torque, and fundamentally avoids damage to the bellows by lateral forces, thus extending the service life of the sealing components.

[0021] In this embodiment, the length ratio of the power arm to the resistance arm is 6:1. This ratio is optimized for the 15-20N tripping force required by the half-shaft of the gas-insulated switchgear circuit breaker and the output force of the bistable permanent magnet mechanism. While ensuring sufficient tripping torque, the axial displacement of the bellows is controlled within the range of 2-3mm.

[0022] This technical solution employs a 6:1 optimized lever arm ratio to precisely address issues such as insufficient tripping torque, excessive bellows displacement, and bulky mechanism size caused by unreasonable lever arm ratios in traditional tripping devices. This ratio balances tripping reliability with component protection, ensuring sufficient tripping torque and reliable circuit breaker tripping while strictly controlling bellows axial displacement, extending the life of sealing components, and guaranteeing a leak-free sealing effect.

[0023] In this embodiment, the bellows dynamic sealing assembly is made of 304 stainless steel hydroformed thin-walled bellows. One end of the bellows is sealed to the fully sealed isolation mounting base by laser welding, and the other end is coaxially laser welded to the transmission push rod. The transmission push rod passes through the inner cavity of the bellows and is coaxially hinged to the central push rod of the internal bistable permanent magnet mechanism through a spherical bearing to ensure transmission accuracy and sealing reliability.

[0024] This technical solution addresses the shortcomings of traditional seals, such as poor corrosion resistance, unreliable sealing, low transmission accuracy, and susceptibility to damage, through an integrated design. It combines excellent sealing with precise transmission performance. Made of 304 stainless steel, it is suitable for long-term operating conditions. Laser welding eliminates leakage, and the spherical hinge ensures error-free transmission. Its simplified structure and strong adaptability eliminate the need for additional protective components. While achieving leak-free power transmission, it extends component life, significantly improves the overall reliability and adaptability of the device, and meets the maintenance-free requirements of gas-insulated switchgear.

[0025] Beneficial Effects: The device employs a bistable permanent magnet locking electromagnetic drive mechanism that maintains closing during power failure and trips with instantaneous excitation during voltage loss. It features zero power consumption under normal conditions, avoiding long-term coil losses and extending service life. The closed magnetic circuit design improves magnetic flux utilization, and the IP68-rated sealed aviation plug is compatible with SF6 sealed conditions in gas-filled cabinets. The bellows dynamic sealing assembly uses a 304 stainless steel hydroformed structure with double-end laser welding seals to prevent gas leakage. A fixed-distance sleeve with quantitative pre-compression ensures coaxial force distribution, and triple coaxial drive force ensures sensitive tripping. A 6:1 optimized lever ratio precisely matches the tripping force requirements, controlling bellows displacement within the optimal range. The horizontal through-slot and spherical hinge achieve gapless, lateral force-free transmission, protecting the sealing components. The overall structure is compact and highly adaptable, requiring no modification to the original cabinet. It achieves coordinated linkage of drive, sealing, and transmission, solving the drawbacks of traditional devices such as poor reliability, easy leakage, and short lifespan, significantly improving operational stability and maintenance-free periods. Attached Figure Description

[0026] Figure 1 A three-dimensional structural schematic diagram of the gas-insulated switchgear underpressure trip protection device provided in the embodiments of this application;

[0027] Figure 2 A three-dimensional structural schematic diagram of the drive mechanism and transmission mechanism provided in the embodiments of this application;

[0028] Figure 3 A cross-sectional structural schematic diagram of the drive mechanism provided in an embodiment of this application;

[0029] The following are the labeling elements in the figure:

[0030] 1. Operating mechanism; 11. Circuit breaker tripping; 2. Drive mechanism; 21. Mounting base; 211. Horizontal through groove; 22. Bellows dynamic seal assembly; 221. Bellows; 23. External magnetic yoke; 24. Ring permanent magnet; 25. Upper stationary iron core; 26. Lower stationary iron core; 27. Moving iron core assembly; 28. Instantaneous excitation coil; 29. ​​Trip drive spring; 3. Transmission mechanism; 31. Power arm; 32. Lever fulcrum; 33. Resistance arm. Detailed Implementation

[0031] In order to improve the undervoltage tripping device of the gas-insulated switchgear circuit breaker in the relevant technology, which is used to trip the circuit when the secondary circuit loses power to avoid the expansion of the main circuit fault, the existing device has obvious defects: the single coil is prone to burnout when energized for a long time, the mechanism is prone to jamming and failure when exposed to SF6 gas chamber, the tripping force is fixed and cannot adapt to the fluctuation of operating conditions and is prone to failure to operate, and it cannot stably achieve reliable tripping, which poses a major safety hazard. The embodiments of this application provide the following solution.

[0032] Please refer to the following: Figures 1 to 3 This application provides a gas-insulated switchgear undervoltage trip protection device. The gas-insulated switchgear undervoltage trip protection device is installed on any fixable plane of the gas-insulated switchgear circuit breaker operating mechanism 1. It is used to trigger the circuit breaker to trip 11 when the secondary circuit loses power or the voltage is lower than a set threshold. It includes a drive mechanism 2 and a transmission mechanism 3.

[0033] The drive mechanism 2 is a bistable permanent magnet locking electromagnetic drive mechanism that maintains closing when power is lost and opens when voltage is lost. In the sealed chamber of the fully sealed isolation mounting base 21, the base achieves leakage-free power output through the bellows dynamic sealing assembly 22.

[0034] The transmission mechanism 3 is a single-fulcrum force amplification lever. The short end of the lever power arm 31 is connected to the bellows 221 transmission push rod in a sliding hinge transmission connection. The end of the lever resistance arm 33 is provided with an arc-shaped trigger head, which directly abuts against the trigger plane of the circuit breaker tripping half shaft to achieve impact-free tripping triggering.

[0035] The gas-insulated switchgear underpressure trip protection device provided in this application embodiment uses a single-pivot force amplification lever as an intermediate transmission connecting component to smoothly convert the small linear output motion of the bistable permanent magnet drive mechanism 2 into the rotational tripping motion of the circuit breaker tripping half-shaft 11. The short end of the lever power arm 31 is slidably hinged to the bellows 221 transmission push rod, which can adapt to assembly tolerances and motion angle deviations, eliminate transmission lateral forces, and protect the bellows dynamic sealing assembly 22 from off-center load wear. The end of the lever resistance arm 33 is provided with an arc-shaped trigger head, which flexibly fits with the trigger plane of the tripping half-shaft to transmit force. It not only relies on the lever ratio to amplify the small input force to a sufficient tripping torque, but also avoids rigid impact, so that the permanent magnet drive, sealing transmission and circuit breaker tripping mechanism are precisely matched and linked, and the whole machine transmission is smooth and without jamming.

[0036] In this embodiment, the bistable permanent magnet locking electromagnetic drive mechanism 2 includes an outer magnetic yoke 23, an axially magnetized annular permanent magnet 24, an upper stationary iron core 25, a lower stationary iron core 26, a moving iron core assembly 27, and an instantaneous excitation coil 28. The annular permanent magnet 24 is axially clamped between the upper and lower stationary iron cores 26 and press-fitted into the inner cavity of the outer magnetic yoke 23 to form a closed magnetic circuit. The moving iron core assembly 27 is coaxially installed in the central guide hole of the upper and lower stationary iron cores 26, and its lower end of the central push rod is coaxially adaptively connected to the transmission push rod of the bellows 221 through a spherical hinge. The instantaneous excitation coil 28 is wound around the inner cavity of the outer magnetic yoke 23 outside the annular permanent magnet 24, and the terminal is led out from the sealed housing through an IP68-level sealed aviation plug to access the secondary control circuit.

[0037] With this configuration, the bistable permanent magnet locking electromagnetic drive mechanism 2 of this scheme adopts an externally guided magnetic yoke 23 paired with an axially magnetized annular permanent magnet 24. The annular permanent magnet 24 is axially clamped between the upper and lower stationary iron cores 26 and interference-fitted into the inner cavity of the yoke, which can construct a regular closed magnetic circuit with high magnetic flux utilization and low leakage magnetic loss. It can stably achieve bistable working characteristics of steady-state permanent magnet holding when the circuit is closed and instantaneous magnetic circuit decoupling when the circuit is lost. The moving iron core assembly 27 is coaxially fitted into the central guide hole of the upper and lower stationary iron cores 26 to ensure high coaxiality of reciprocating motion and no swaying or jamming during operation. The central push rod and the bellows 221 transmission push rod adopt a spherical hinge structure, which has the ability to adaptively compensate for angles and can offset the lateral stress caused by assembly tolerances and motion angle. The instantaneous excitation coil 28 is built into the inner cavity of the yoke and is connected to the IP68-level sealed aviation plug, which has a high level of sealing protection and can effectively isolate SF6 gas, moisture and dust corrosion inside the cabinet.

[0038] In this embodiment, the bellows dynamic sealing assembly 22 is pre-compressed quantitatively by a spacer sleeve during assembly, so that the bellows 221 always maintains a pre-compression elastic force that is completely coaxial with the thrust direction of the tripping drive spring 29 when the circuit is closed and locked.

[0039] When the secondary circuit loses voltage, the instantaneous excitation coil 28 is supplied with a reverse pulse current to counteract the permanent magnet holding force. The moving iron core is simultaneously driven by the main thrust of the tripping drive spring 29, the auxiliary elastic force of the bellows 221, and its own gravity in a triple coaxial drive. The resultant force is without component loss along the axis of the moving iron core, and the tripping action is completed quickly.

[0040] This configuration allows the fixed-distance sleeve quantitative pre-compression structure to align the force axes of the bellows 221, the tripping drive spring 29, and the moving iron core assembly 27, achieving a mechanical match between the sealing and driving components. This allows the bellows 221 to both perform the dynamic sealing and isolation function for SF6 gas and simultaneously output auxiliary driving force, simplifying the overall layout with a single component serving two purposes. The triple coaxial drive mode precisely coordinates with the decoupling action of the bistable permanent magnet mechanism. After the reverse pulse cancels out the permanent magnet holding force, the multi-source combined force is released axially without loss and smoothly transmitted to the rear lever transmission mechanism 3, avoiding jamming and output attenuation during power transmission. This achieves smooth linkage between electromagnetic unlocking, combined force drive, and mechanical tripping.

[0041] In this embodiment, a horizontal through groove 211 perpendicular to the direction of push rod movement is provided on the output shaft of the bellows 221 drive push rod. The lever fulcrum 32 is located on the extension line of the output shaft of the bellows 221 drive push rod. The short end of the lever power arm 31 is slidably located in the horizontal through groove 211 through a cylindrical pin, realizing the seamless conversion of linear motion to circular motion, and no lateral force is applied to the bellows 221 during the transmission process.

[0042] This design enables precise connection between the bellows 221 drive push rod and the single-fulcrum force amplification lever. The sliding fit between the horizontal through groove 211 and the cylindrical pin adapts to the angular deviation between the lever's circular motion and the push rod's linear motion, ensuring smooth and unobstructed transmission. The coaxial layout of the fulcrum and the extended line of the push rod's output shaft allows the axial driving force output by the push rod to be efficiently converted into a tripping torque through the lever, without additional force loss, achieving mechanical adaptation between the drive mechanism 2, the transmission mechanism 3, and the circuit breaker tripping half-shaft 11. Simultaneously, the lateral force-free design protects the bellows dynamic sealing assembly 22, ensuring its long-term stable and leak-free power output. This allows the permanent magnet drive, sealed transmission, and lever amplification systems to work synergistically, improving the overall reliability of the machine.

[0043] In this embodiment, the length ratio of the power arm 31 to the resistance arm 33 is 6:1. This ratio is optimized for the 15-20N tripping force required by the half-shaft of the gas-insulated switchgear circuit breaker 11 and the output force of the bistable permanent magnet mechanism. While ensuring sufficient tripping torque, the axial displacement of the bellows 221 is controlled within the range of 2-3mm.

[0044] This configuration, with a lever arm ratio of 6:1 as the core design of the transmission mechanism 3, achieves precise mechanical connection between the bistable permanent magnet drive mechanism 2, the bellows dynamic sealing assembly 22, and the circuit breaker tripping half-shaft 11. Simultaneously, limiting the axial displacement of the bellows 221 to 2-3mm allows for coordinated operation with the spacer sleeve pre-compression structure and the spherical hinge structure, preventing excessive displacement from damaging the sealing performance of the bellows 221. This ensures that power is smoothly transmitted from the permanent magnet mechanism through the bellows 221 and the lever to the tripping half-shaft, achieving mechanical matching and smooth linkage between the drive, sealing, and transmission systems.

[0045] In this embodiment, the bellows dynamic sealing assembly 22 adopts a 304 stainless steel hydroformed thin-walled bellows 221. One end of the bellows is sealed to the fully sealed isolation mounting base 21 by laser welding, and the other end is coaxially laser welded to the transmission push rod. The transmission push rod passes through the inner cavity of the bellows 221 and is coaxially hinged to the central push rod of the internal bistable permanent magnet mechanism through a spherical bearing to ensure transmission accuracy and sealing reliability.

[0046] With this configuration, the bellows dynamic sealing assembly 22 adopts a thin-walled structure formed by hydroforming of 304 stainless steel. The material is resistant to SF6 gas corrosion, exhibits excellent fatigue resistance, and demonstrates superior high and low temperature performance. Hydroforming ensures uniform wall thickness and consistent deformation, making it suitable for the harsh operating conditions of gas-filled cabinets. Both ends are coaxially laser-welded for sealing, resulting in high strength and excellent sealing performance, preventing SF6 leakage and impurity intrusion, and ensuring the insulation and stability of the internal electromagnetic components. The transmission push rod and the permanent magnet mechanism's central push rod are coaxially hinged via a spherical bearing, ensuring transmission accuracy, adapting to assembly deviations, avoiding lateral forces, and further improving sealing and smooth operation.

[0047] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A gas-insulated switchgear undervoltage trip protection device, installed on any fixable plane of the gas-insulated switchgear circuit breaker operating mechanism (1), used to trigger the circuit breaker to trip (11) when the secondary circuit loses power or the voltage is lower than a set threshold, comprising a drive mechanism (2) and a transmission mechanism (3), characterized in that: The drive mechanism (2) is a bistable permanent magnet locking electromagnetic drive mechanism (2) that maintains closing when power is lost and opens when excitation is lost due to pressure. In the sealed chamber of the fully sealed isolation mounting base (21), the base achieves leakage-free power output through the bellows dynamic sealing assembly (22). The transmission mechanism (3) is a single-pivot force amplification lever. The short end of the lever power arm (31) is connected to the bellows (221) transmission push rod in a sliding hinge transmission connection. The end of the lever resistance arm (33) is provided with an arc-shaped trigger head, which directly abuts against the trigger plane of the circuit breaker tripping (11) half shaft to achieve impact-free tripping triggering.

2. An under-voltage tripping protection device for an air insulated switchgear according to claim 1, characterized in that: The bistable permanent magnet locking electromagnetic drive mechanism (2) includes an outer magnetic yoke (23), an axially magnetized annular permanent magnet (24), an upper stationary iron core (25), a lower stationary iron core (26), a moving iron core assembly (27), and an instantaneous excitation coil (28). The annular permanent magnet (24) is axially clamped between the upper and lower stationary iron cores (26) and press-fitted into the inner cavity of the outer magnetic yoke (23) to form a closed magnetic circuit. The moving iron core assembly (27) is coaxially installed in the central guide hole of the upper and lower stationary iron cores (26), and its central push rod is coaxially adaptively connected to the bellows (221) transmission push rod through a spherical hinge. The instantaneous excitation coil (28) is wound around the inner cavity of the outer magnetic yoke (23) outside the annular permanent magnet (24), and the wiring terminal is led out from the sealed housing through an IP68-level sealed aviation plug to access the secondary control circuit.

3. An under-voltage tripping protection device for an air insulated switchgear according to claim 2, characterized in that: During assembly, the bellows dynamic sealing assembly (22) is pre-compressed quantitatively by a spacer sleeve so that the bellows (221) always maintains a pre-compression force that is completely coaxial with the thrust direction of the tripping drive spring (29) when the circuit is locked. When the secondary circuit loses voltage, the instantaneous excitation coil (28) is supplied with a reverse pulse current to counteract the permanent magnet holding force. The moving iron core is simultaneously driven by the main thrust of the tripping drive spring (29), the auxiliary elastic force of the bellows (221), and its own gravity in a triple coaxial drive. The resultant force is without component loss along the axis of the moving iron core, and the tripping action is completed quickly.

4. An under-voltage trip protection device for an air insulated switchgear according to claim 1 or 2, characterized in that: A horizontal through groove (211) perpendicular to the direction of push rod movement is provided on the output shaft of the bellows (221) drive push rod. The lever fulcrum (32) is located on the extension line of the output shaft of the bellows (221) drive push rod. The short end of the lever power arm (31) is slidably set in the horizontal through groove (211) through a cylindrical pin, realizing the seamless conversion of linear motion to circular motion, and no lateral force is applied to the bellows (221) during the transmission process.

5. An under-voltage trip protection device for an air insulated switchgear according to claim 4, characterized in that: The length ratio of the power arm (31) to the resistance arm (33) is 6:

1. The 15-20N tripping force and the output force of the bistable permanent magnet mechanism required for the half shaft of the gas-filled switchgear circuit breaker (11) are optimized to ensure sufficient tripping torque while controlling the axial displacement of the bellows (221) within the range of 2-3mm.

6. The loss of pressure trip protection apparatus for an air insulated switchgear according to claim 2, characterized in that: The bellows dynamic sealing assembly (22) is made of 304 stainless steel hydroformed thin-walled bellows (221). One end of the bellows is sealed to the fully sealed isolation mounting base (21) by laser welding, and the other end is coaxially laser welded to the transmission push rod. The transmission push rod passes through the inner cavity of the bellows (221) and is coaxially hinged to the central push rod of the internal bistable permanent magnet mechanism through a spherical bearing to ensure transmission accuracy and sealing reliability.

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