Medium voltage gas-insulated metal-enclosed switchgear

Abstract

The application discloses a kind of medium-pressure inflatable metal-enclosed switchgear, belong to power transmission and distribution switchgear technical field;The device includes gas tank, sealed installation in gas tank has incoming line side three-position switch unit, circuit breaker unit, outgoing line side three-position switch unit, fast grounding switch and branch bus, and the top of gas tank is arranged with incoming line cable and outgoing line cable;Incoming line cable is connected with the intermediate static contact of incoming line side three-position switch unit, the isolation static contact of incoming line side three-position switch unit is connected with the movable contact end of circuit breaker unit, and the static contact end of circuit breaker unit is connected with branch bus and outgoing line side three-position switch unit respectively, and the intermediate static contact of outgoing line side three-position switch unit is connected with outgoing line cable and the static contact of fast grounding switch.The high voltage functional unit of the application is integrated in the same gas tank, realizes the compact arrangement of equipment, can be adapted to offshore wind power and other narrow installation space, while realizing fast fault isolation protection.

Description

Technical Field

[0001] This invention relates to the field of power transmission and distribution switchgear technology, specifically to a medium-voltage gas-insulated metal-enclosed switchgear, which is suitable for applications such as offshore wind power and high-altitude substations where there are high requirements for equipment compactness, reliability, and environmental adaptability. It can realize the functions of safe control, transmission, and fault isolation protection of electrical energy. Background Technology

[0002] With the rapid development of new energy projects such as deep-sea wind power, the number of wind farms located more than 100 kilometers offshore is increasing. Offshore wind power projects have extremely limited space. To reduce the number of turbine circuits, save substation space, and lower investment and operation and maintenance costs, the voltage level of wind farm power collection systems is gradually increasing (e.g., 66kV / 72.5kV). This leads to a growing demand for gas-insulated metal-enclosed switchgear of corresponding medium-voltage levels. The internal installation space of wind towers is extremely limited, placing extremely stringent requirements on switchgear: it must be compactly arranged within the space-constrained wind turbine tower and withstand the extreme marine environment of high salt spray, high humidity, and strong vibration, while also requiring extremely high operational reliability and ease of maintenance, favoring maintenance-free designs.

[0003] Currently, the mainstream solution for this voltage level in the market is the traditional SF6 gas-insulated switchgear (GIS). However, existing technologies have the following significant shortcomings:

[0004] First, environmental and policy pressures are increasingly prominent: SF6 is a globally recognized strong greenhouse gas, with a global warming potential (GWP) 23,500 times that of CO2. It is extremely difficult to degrade in the atmosphere, persisting for over 3,200 years. With the deepening implementation of the Paris Agreement, the procurement, use, and recycling of SF6 face increasingly stringent environmental regulations and rising costs. The EU has explicitly required the phase-out of SF6 from 145kV and below switchgear by 2028, making related technological transformation imperative.

[0005] Secondly, the equipment is large and lacks spatial adaptability: Conventional GIS systems mostly adopt a decentralized layout, with high-voltage functional units (circuit breakers, disconnect switches, grounding switches, etc.) independently encapsulated in different gas chambers. The overall integration is low and the size is large, making it difficult to directly adapt to the narrow installation space of offshore wind turbine towers. Existing gas-insulated switchgear is mostly divided into multiple independent parts according to the principle of incoming and outgoing lines. One gas-insulated switchgear can only supply power to one device at a time. If the power supply requirements of more circuits or more complex topologies need to be met, the number of gas-insulated switchgears needs to be increased, further encroaching on the already limited space.

[0006] Third, high inflation pressure leads to insufficient sealing and long-term reliability: Conventional GIS typically requires high inflation pressures (e.g., 0.6–0.8 MPa) to achieve rated insulation levels. High-pressure SF6 gas places extremely high demands on equipment sealing performance and casing strength, increasing manufacturing difficulty and cost. Simultaneously, the risk of gas leakage increases under high-pressure conditions, requiring regular gas replenishment and maintenance during long-term operation, making it difficult to achieve the maintenance-free goal desired by offshore wind power.

[0007] Fourth, integrating the rapid grounding function is difficult: Existing low-pressure gas-filled switchgear often sacrifices the response speed of the mechanism to meet the requirements of large insulation break distances. How to achieve reliable operation of the rapid grounding switch with a large stroke under low-pressure conditions and effectively integrate it into a compact gas chamber is a problem that current technology has not yet solved well. Conventional solutions often suffer from insufficient stroke and complex mechanisms due to space and transmission limitations.

[0008] In summary, existing medium-voltage gas-insulated switchgear has significant shortcomings in terms of compactness, reliability under low pressure operation, integration of rapid grounding functionality, and environmental adaptability. It is difficult to fully meet the stringent requirements of high reliability, maintenance-free operation, and compactness in extreme environments such as offshore wind power. Therefore, there is an urgent need to develop a new type of medium-voltage gas-insulated metal-enclosed switchgear with a highly compact structure, reliable operation under low pressure, effective integration of rapid grounding functionality, and suitability for harsh environments such as offshore wind power. Summary of the Invention

[0009] In view of this, the present invention provides a medium-voltage gas-filled metal-enclosed switchgear, which aims to solve the above-mentioned technical problems.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A medium-voltage gas-filled metal-enclosed switchgear includes a gas box, characterized in that the gas box is sealed and installed with an incoming three-position switch unit, a circuit breaker unit, an outgoing three-position switch unit, a fast grounding switch and a branch busbar, and the top of the gas box is arranged with an incoming cable and an outgoing cable. The incoming cable is connected to the intermediate stationary contact of the incoming three-position switch unit. The isolating stationary contact of the incoming three-position switch unit is connected to the moving contact of the circuit breaker unit. The stationary contact of the circuit breaker unit is connected to the branch busbar and the outgoing three-position switch unit respectively. The intermediate stationary contact of the outgoing three-position switch unit is connected to the outgoing cable and the stationary contact of the fast grounding switch.

[0011] Through the above technical solution, this invention seals and installs the circuit breaker unit, the incoming three-position switch unit, the outgoing three-position switch unit, the fast grounding switch, and the branch busbar all in the same gas box, and arranges the incoming and outgoing cables on the top of the gas box. At the same time, it constructs a complete main circuit layout where the incoming cable goes through the incoming three-position switch unit to the circuit breaker unit, and then from the circuit breaker unit, it connects to the branch busbar and the outgoing three-position switch unit to achieve parallel expansion and power output. The outgoing three-position switch unit connects the outgoing cable and the fast grounding switch. This achieves a high degree of integration of high-voltage functional units, greatly reducing the overall size of the equipment. It can directly adapt to the narrow installation space of offshore wind turbine towers, effectively solving the problems of large size and insufficient space adaptability of traditional equipment. At the same time, by directly integrating the fast grounding switch at the end of the main circuit, it realizes instantaneous grounding protection and rapid interruption of fault current under fault conditions, improving the safety and reliability of equipment operation.

[0012] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the circuit breaker unit includes a solid-sealed pole and a mounting aluminum plate. The solid-sealed pole is fixed to the mounting aluminum plate, and the mounting aluminum plate is fixed to the frame of the gas box. One end of the solid-sealed pole is fixed by the mounting aluminum plate, and the other end of the solid-sealed pole is fixed to the frame of the gas box by a post insulator, forming a support structure with fixed ends.

[0013] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, a transmission device is installed on the mounting aluminum plate. The transmission device includes a bellows transmission structure and a first transmission shaft, which are mounted on the frame.

[0014] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, both the incoming three-position switch unit and the outgoing three-position switch unit include a grounding stationary contact, an intermediate stationary contact, a first moving contact, and an isolation stationary contact. The intermediate stationary contact is fixed inside the gas box using a two-point support structure.

[0015] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the incoming three-position switch unit is provided with an incoming three-position mechanism, and the outgoing three-position switch unit is provided with an outgoing three-position mechanism. Both the incoming three-position mechanism and the outgoing three-position mechanism drive the first moving contact to reciprocate through a transmission sprocket and a second transmission shaft to realize the three-position isolation and grounding switching.

[0016] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the width of the gas box is 1 meter, and the branch busbars adopt a laterally extended busbar arrangement.

[0017] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the circuit breaker unit is provided with a corresponding circuit breaker mechanism, which is arranged outside the gas box.

[0018] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the fast grounding switch includes a stationary contact, a second moving contact, a crank arm box, and an operating mechanism. The stationary contact is installed on the main circuit, the second moving contact is connected to the crank arm box, and the operating mechanism is driven by the crank arm box. The second moving contact reciprocates under the drive of the operating mechanism through the crank arm box.

[0019] Preferably, in the above-mentioned medium-voltage gas-filled metal-enclosed switchgear, the operating mechanism of the fast grounding switch is fixed to the crank arm box, and the operating mechanism is arranged outside the gas box.

[0020] Preferably, in the above-mentioned medium-voltage gas-insulated metal-enclosed switchgear, an incoming surge arrester is correspondingly provided at the incoming cable, an outgoing surge arrester is correspondingly provided at the outgoing cable, an incoming-side post insulator is provided between the incoming-side three-position switch unit and the circuit breaker unit, and an outgoing-side post insulator is provided between the circuit breaker unit and the outgoing-side three-position switch unit.

[0021] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a medium-voltage gas-filled metal-enclosed switchgear, which has the following beneficial effects: 1. This invention achieves a high degree of integration of high-voltage functional units by sealing and installing the circuit breaker unit, the incoming three-position switch unit, the outgoing three-position switch unit, the fast grounding switch, and the branch busbars all in the same gas box. The gas box is only 1 meter wide. With the side-expanded busbar arrangement, the overall size and height are greatly reduced. It can be directly adapted to narrow installation spaces such as offshore wind turbine towers, effectively solving the problems of large size and insufficient spatial adaptability of traditional GIS.

[0022] 2. The present invention adopts a two-end fixed support structure for the circuit breaker solid-sealed pole. One end is fixed by mounting aluminum plate, and the other end is fixed to the gas box frame by post insulator. This greatly enhances the structural strength and seismic resistance of the solid-sealed pole, effectively suppresses contact bounce during circuit breaker closing operation, and improves electrical life and operational stability.

[0023] 3. The present invention adopts a two-point support structure for the intermediate stationary contact of the three-position switch. Compared with the traditional single-point support, it significantly improves the mechanical strength and positioning accuracy of the intermediate stationary contact, ensures strict coaxiality between the intermediate stationary contact and the isolation stationary contact and the grounding stationary contact, and guarantees the operational reliability of the three-position switch.

[0024] 4. The fast grounding switch of the present invention can instantly force the main circuit to ground within milliseconds when a fault occurs inside the gas box, and trigger the circuit breaker to cut off the fault current, thus realizing fast and reliable fault isolation protection and solving the contradiction between the large-stroke reliable operation of the fast grounding switch and compact integration under low gas pressure conditions.

[0025] 5. The circuit breaker mechanism, three-position mechanism and fast grounding switch operating mechanism of the present invention are all arranged outside the gas box, which facilitates the realization of electrical and mechanical interlocking between the mechanisms and greatly facilitates the operation, observation and subsequent maintenance of on-site personnel. There is no need to enter or open the high-pressure gas chamber. With the low-pressure sealing design, maintenance-free operation throughout the entire life cycle is achieved. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 The attached figure is a structural schematic diagram of the medium-voltage gas-filled metal-enclosed switchgear provided by the present invention; Figure 2 The attached figure is a structural schematic diagram of the three-position switch unit provided by the present invention; Figure 3 The attached figure is a schematic diagram of the structure of the circuit breaker unit provided by the present invention; Figure 4 The attached figure is a schematic diagram of the structure of the fast grounding switch provided by the present invention.

[0028] in: 1-1 Incoming cable; 1-2 Incoming surge arrester; 1-3 Incoming three-position switch unit; 1-4 Incoming three-position mechanism; 1-5 Incoming post insulator; 1-6 Circuit breaker unit; 1-7 Circuit breaker mechanism; 1-8 Post insulator; 1-9 Outgoing cable; 1-10 Outgoing surge arrester; 1-11 Fast grounding switch; 1-12 Outgoing three-position mechanism; 1-13 Outgoing post insulator; 1-14 Outgoing three-position switch unit. Unit 1-15 is a branch busbar; 1-16 is an air box; 2-1 is a transmission sprocket; 2-2 is a grounding stationary contact; 2-3 is a second transmission shaft; 2-4 is an intermediate stationary contact; 2-5 is a first moving contact; 2-6 is an isolation stationary contact; 3-1 is a solid-sealed pole; 3-2 is a mounting aluminum plate; 3-3 is a bellows transmission structure; 3-4 is a first transmission shaft; 3-5 is a frame; 4-1 is a stationary contact; 4-2 is a second moving contact; 4-3 is a crank arm box; 4-4 is an operating mechanism. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] See appendix Figure 1 To be continued Figure 4 This invention discloses a medium-voltage gas-filled metal-enclosed switchgear.

[0031] As attached Figure 1 As shown, the gas box 1-16 is sealed with an incoming three-position switch unit 1-3, a circuit breaker unit 1-6, an outgoing three-position switch unit 1-14, a fast grounding switch 1-11, and a branch busbar 1-15. The top of the gas box 1-16 is equipped with an incoming cable 1-1 and an outgoing cable 1-9. The incoming cable 1-1 is located at the top of the gas box 1-16 for easy access from the transformer on the upper part of the offshore wind turbine tower.

[0032] The incoming cable 1-1 is connected to the intermediate stationary contact of the incoming-side three-position switch unit 1-3, and the isolating stationary contact of the incoming-side three-position switch unit 1-3 is connected to the moving contact of the circuit breaker unit 1-6. The stationary contact of the circuit breaker unit 1-6 is connected to the branch busbar 1-15 and the outgoing-side three-position switch unit 1-14, respectively, thereby realizing the functions of switchgear expansion and power output. The intermediate stationary contact of the outgoing-side three-position switch unit 1-14 is connected to the stationary contact of the outgoing cable 1-9 and the fast grounding switch 1-11.

[0033] An incoming surge arrester 1-2 is installed at the incoming cable 1-1, and an outgoing surge arrester 1-10 is installed at the outgoing cable 1-9, respectively, to protect the incoming and outgoing sides from overvoltage. An incoming-side post insulator 1-5 is installed between the incoming-side three-position switch unit 1-3 and the circuit breaker unit 1-6, and an outgoing-side post insulator 1-13 is installed between the circuit breaker unit 1-6 and the outgoing-side three-position switch unit 1-14.

[0034] Branch busbars 1-15 adopt a lateral expansion busbar layout, which effectively reduces the overall height of the equipment and is more conducive to installation in containerized substations or offshore wind turbine towers with limited space. The gas box 1-16 is 1 meter wide, and all high-potential components are sealed and installed inside the gas box 1-16, achieving a highly compact integration of the entire unit.

[0035] As attached Figure 3As shown, circuit breaker unit 1-6 includes a solid-sealed pole 3-1 and a mounting aluminum plate 3-2. The solid-sealed pole 3-1 is fixed to the mounting aluminum plate 3-2, which is fixed to the frame of the gas box 1-16. One end of the solid-sealed pole 3-1 is fixed by the mounting aluminum plate 3-2, and the other end is fixed to the frame of the gas box 1-16 by a post insulator 1-8, forming a support structure with fixed ends. This fixed-end support structure greatly enhances the structural strength and seismic resistance of the solid-sealed pole 3-1, effectively suppresses contact bounce during circuit breaker closing operations, and improves electrical life and operational stability.

[0036] A transmission device is mounted on the aluminum plate 3-2. The transmission device includes a bellows transmission structure 3-3 and a first transmission shaft 3-4, which are mounted on the frame 3-5. The circuit breaker mechanism 1-7 is located outside the gas chamber 1-16 and drives the circuit breaker unit 1-6 to perform opening and closing operations via the transmission device. The external location of the circuit breaker mechanism 1-7 facilitates operation, observation, and subsequent maintenance by on-site personnel without requiring entry into or opening of the high-pressure gas chamber.

[0037] As attached Figure 4 As shown, the fast grounding switch 1-11 includes a stationary contact 4-1, a second moving contact 4-2, a crank arm box 4-3, and an operating mechanism 4-4. The stationary contact 4-1 is installed on the main circuit, the second moving contact 4-2 is connected to the crank arm box 4-3, and the operating mechanism 4-4 is driven by the crank arm box 4-3. The operating mechanism 4-4 is fixed on the crank arm box 4-3 and arranged outside the gas box 1-16. Driven by the operating mechanism 4-4, the second moving contact 4-2 reciprocates through the crank arm box 4-3, thereby achieving the function of quickly grounding the main circuit. When an insulation creepage or arcing fault occurs inside the gas box 1-16, the fast grounding switch 1-11 can instantly force the main circuit to ground within milliseconds and trigger the circuit breaker unit 1-6 to cut off the fault current, quickly isolate the fault, and protect the equipment.

[0038] As attached Figure 2 As shown, both the incoming-side three-position switch unit 1-3 and the outgoing-side three-position switch unit 1-14 include a grounding stationary contact 2-2, an intermediate stationary contact 2-4, a first moving contact 2-5, and an isolating stationary contact 2-6. The intermediate stationary contact 2-4 of the incoming-side three-position switch unit 1-3 is connected to the incoming cable 1-1, and the intermediate stationary contact 2-4 of the outgoing-side three-position switch unit 1-14 is connected to the outgoing cable 1-9 and the stationary contact of the fast grounding switch 1-11.

[0039] The intermediate stationary contact 2-4 is fixed in the gas box 1-16 with a two-point support structure. Compared with the traditional single-point support structure, the two-point support significantly improves the mechanical strength and positioning accuracy of the intermediate stationary contact 2-4, ensuring strict coaxiality between the intermediate stationary contact 2-4, the isolating stationary contact 2-6, and the grounding stationary contact 2-2, thus ensuring the operational reliability of the three-position switch.

[0040] The incoming-side three-position switch unit 1-3 is equipped with an incoming-side three-position mechanism 1-4, and the outgoing-side three-position switch unit 1-14 is equipped with an outgoing-side three-position mechanism 1-12. Both the incoming-side and outgoing-side three-position mechanisms 1-4 and 1-12 are located outside the gas box 1-16, facilitating electrical and mechanical interlocking between the mechanisms and simplifying operation and maintenance by on-site personnel. Both the incoming-side and outgoing-side three-position mechanisms 1-4 and 1-12 are driven by a transmission sprocket 2-1 and a second transmission shaft 2-3 to reciprocate the first moving contact 2-5, achieving three-position isolation and grounding operation. When the first moving contact 2-5 contacts the isolating stationary contact 2-6, isolation is achieved; when the first moving contact 2-5 contacts the grounding stationary contact 2-2, grounding is achieved; and when the first moving contact 2-5 is in the intermediate position, isolation is in the open state.

[0041] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A medium-voltage gas-filled metal-enclosed switchgear, comprising a gas box (1-16), characterized in that, The gas box (1-16) is sealed and installed with an incoming three-position switch unit (1-3), a circuit breaker unit (1-6), an outgoing three-position switch unit (1-14), a fast grounding switch (1-11), and a branch busbar (1-15). The top of the gas box (1-16) is arranged with an incoming cable (1-1) and an outgoing cable (1-9). The incoming cable (1-1) is connected to the intermediate stationary contact of the incoming three-position switch unit (1-3). The isolating stationary contact of the incoming three-position switch unit (1-3) is connected to the moving contact of the circuit breaker unit (1-6). The stationary contact of the circuit breaker unit (1-6) is connected to the branch bus (1-15) and the outgoing three-position switch unit (1-14) respectively. The intermediate stationary contact of the outgoing three-position switch unit (1-14) is connected to the outgoing cable (1-9) and the stationary contact of the fast grounding switch (1-11).

2. The medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, The circuit breaker unit (1-6) includes a solid-sealed pole (3-1) and a mounting aluminum plate (3-2). The solid-sealed pole (3-1) is fixed on the mounting aluminum plate (3-2), and the mounting aluminum plate (3-2) is fixed on the frame of the gas box (1-16). One end of the solid-sealed pole (3-1) is fixed by the mounting aluminum plate (3-2), and the other end of the solid-sealed pole (3-1) is fixed to the frame of the gas box (1-16) by a post insulator (1-8), forming a support structure fixed at both ends.

3. A medium-voltage gas-filled metal-enclosed switchgear according to claim 2, characterized in that, A transmission device is installed on the mounting aluminum plate (3-2). The transmission device includes a bellows transmission structure (3-3) and a first transmission shaft (3-4). The bellows transmission structure (3-3) and the first transmission shaft (3-4) are mounted on the frame (3-5).

4. A medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, The incoming three-position switch unit (1-3) and the outgoing three-position switch unit (1-14) both include a grounding stationary contact (2-2), an intermediate stationary contact (2-4), a first moving contact (2-5), and an isolation stationary contact (2-6). The intermediate stationary contact (2-4) is fixed inside the gas box (1-16) using a two-point support structure.

5. A medium-voltage gas-filled metal-enclosed switchgear according to claim 4, characterized in that, The incoming three-position switch unit (1-3) is provided with an incoming three-position mechanism (1-4), and the outgoing three-position switch unit (1-14) is provided with an outgoing three-position mechanism (1-12). Both the incoming three-position mechanism (1-4) and the outgoing three-position mechanism (1-12) drive the first moving contact (2-5) to reciprocate through the transmission sprocket (2-1) and the second transmission shaft (2-3) to realize the three-position isolation and grounding switching.

6. A medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, The width of the air box (1-16) is 1 meter, and the branch busbar (1-15) adopts a laterally extended busbar arrangement.

7. A medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, The circuit breaker unit (1-6) is provided with a corresponding circuit breaker mechanism (1-7), which is arranged outside the gas box (1-16).

8. A medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, The fast grounding switch (1-11) includes a stationary contact (4-1), a second moving contact (4-2), a crank arm box (4-3), and an operating mechanism (4-4). The stationary contact (4-1) is installed on the main circuit. The second moving contact (4-2) is connected to the crank arm box (4-3). The operating mechanism (4-4) is driven by the crank arm box (4-3) to achieve reciprocating motion.

9. A medium-voltage gas-filled metal-enclosed switchgear according to claim 8, characterized in that, The operating mechanism (4-4) of the fast grounding switch (1-11) is fixed on the crank arm box (4-3), and the operating mechanism (4-4) is arranged outside the gas box (1-16).

10. A medium-voltage gas-filled metal-enclosed switchgear according to claim 1, characterized in that, An incoming surge arrester (1-2) is installed at the incoming cable (1-1), and an outgoing surge arrester (1-10) is installed at the outgoing cable (1-9). An incoming-side post insulator (1-5) is installed between the incoming-side three-position switch unit (1-3) and the circuit breaker unit (1-6), and an outgoing-side post insulator (1-13) is installed between the circuit breaker unit (1-6) and the outgoing-side three-position switch unit (1-14).

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