A semi-indoor arranged back-to-back hvdc station start-up circuit

Abstract

The application discloses a kind of half indoor arrangement's back-to-back hvdc converter station starting loop, comprising: several groups of bridge arm reactor, the bridge arm reactor includes juxtaposition operation's first bridge arm reactor and second bridge arm reactor;The side of first bridge arm reactor is connected to bypass disconnecting switch;The side of second bridge arm reactor is connected to starting resistance by support insulator;Starting resistance and branch current measuring device are connected in series, and the starting resistance is connected in parallel with the bypass disconnecting switch and then connected in series with loop current measuring device;The loop current measuring device is connected in series with voltage measuring device, HGIS and starting loop lightning arrester in turn.This application can reduce the noise influence of equipment, avoid the solarization aging of reactor, slow down the aging of protective layer on the surface of reactor, effectively reduce the dirt of external insulation of equipment, reduce the influence of dust and external environment on equipment, and is conducive to the operation and maintenance of equipment.

Description

Technical Field

[0001] This invention relates to the field of converter station layout technology, and in particular to a start-up circuit for a semi-indoor back-to-back flexible DC converter station. Background Technology

[0002] With the development of my country's economy, the power grid structure has become increasingly complex, presenting three major problems: mutual interference between AC and DC power grids, excessively high short-circuit current levels in the main grid, and the risk of large-scale power outages, affecting the flexibility of the main grid operation. Back-to-back DC projects offer a good solution for optimizing the power grid structure, preserving and maintaining the power exchange capacity of existing channels and continuing to leverage the benefits of interconnected capacity; providing emergency support in case of accidents; and in the long term, back-to-back DC projects will also serve as accident isolation.

[0003] Back-to-back starting circuits serve as interconnection channels between two power grids, typically located in densely populated areas with high urbanization levels and surrounding residential communities. Existing back-to-back starting circuits are all outdoor-mounted. However, outdoor installation of the starting circuit results in significant noise generation from the reactors during operation, requiring substantial noise reduction. Furthermore, the reactors are generally located in the center of the substation area, with connecting equipment on both sides, generating considerable heat during operation. Installing sound barriers is difficult and has limited effectiveness, making noise reduction challenging. Additionally, the starting circuit area has tall equipment, occupying a large area, and its outdoor placement severely impacts the sensory experience of residents around the substation. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a semi-indoor arrangement of a back-to-back flexible DC converter station start-up circuit, thereby reducing the noise and sensory impact of the converter station on the surrounding environment.

[0005] This invention provides a startup circuit for a semi-indoor back-to-back flexible DC converter station, the startup circuit comprising:

[0006] Several groups of bridge arm reactors, wherein the bridge arm reactors include a first bridge arm reactor and a second bridge arm reactor operating in parallel;

[0007] One side of the first bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side of the first bridge arm reactor is connected to a bypass disconnect switch;

[0008] One side of the second bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side of the second bridge arm reactor is connected to the starting resistor via a post insulator.

[0009] The starting resistor is connected in series with the branch current measuring device, and the starting resistor is connected in parallel with the bypass disconnect switch and then connected in series with the loop current measuring device.

[0010] The circuit current measuring device is connected in series with the voltage measuring device, the HGIS high-voltage switchgear and the starting circuit surge arrester. The starting circuit surge arrester is connected to the flexible DC transformer bushing in the flexible DC transformer room through the post insulator and the cross-circuit busbar.

[0011] Furthermore, the first bridge arm reactor and the second bridge arm reactor are in phase sequence, and the first bridge arm reactor and the second bridge arm reactor are respectively connected in parallel with a first reactor surge arrester and a second reactor surge arrester.

[0012] Furthermore, the bypass disconnect switch and the starting resistor are arranged side by side, and the branch current measuring device is arranged between the bypass disconnect switch and the starting resistor.

[0013] Furthermore, the loop current measuring device is arranged side by side with the HGIS high-voltage switchgear, and the voltage measuring device and the starting loop surge arrester are respectively arranged on both sides of the HGIS high-voltage switchgear.

[0014] Furthermore, the voltage measuring device and the starting circuit surge arrester are arranged side by side, and the voltage measuring device and the starting circuit surge arrester are arranged in parallel with the HGIS high-voltage switchgear.

[0015] Furthermore, a steel structure column is arranged on the side of the bridge arm reactor facing the start-up circuit surge arrester, and walls are arranged on the other three sides of the bridge arm reactor, with a wall top arranged above the walls.

[0016] Furthermore, the distance from the steel structure column to the center of the bridge arm reactor is a preset multiple of the diameter of the bridge arm reactor.

[0017] Furthermore, the bridge arm reactor is a dry-type air-core reactor.

[0018] Furthermore, the preset multiple is 2.6 times.

[0019] The present invention provides a semi-indoor back-to-back flexible DC converter station start-up circuit. By arranging the start-up circuit semi-indoor, noise propagation is blocked, effectively reducing the noise impact of the reactor on the station's operating personnel and the surrounding environment. Furthermore, it eliminates the need for rain covers, saving manpower and material resources. It also avoids the aging of the reactor's surface protective layer caused by sun exposure, effectively reducing the accumulation of dirt on the equipment's external insulation, and reducing the impact of dust and the external environment on the equipment, which is beneficial to the operation and maintenance of the equipment. Attached Figure Description

[0020] Figure 1 This is a plan view of the start-up circuit of a back-to-back flexible DC converter station arranged in a semi-indoor configuration according to an embodiment of the present invention.

[0021] Figure 2 This is a wiring diagram of the start-up circuit of a semi-indoor back-to-back flexible DC converter station provided in an embodiment of the present invention.

[0022] Figure 3 This is a plan view of the start-up circuit of the outdoor back-to-back flexible DC converter station provided in an embodiment of the present invention;

[0023] Figure 4 This is a cross-sectional view of the start-up circuit of an outdoor back-to-back flexible DC converter station provided in an embodiment of the present invention.

[0024] Figure 5 This is a cross-sectional view of the start-up circuit of a back-to-back flexible DC converter station with a semi-indoor layout provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0026] Please see Figure 1 The present invention proposes a semi-indoor back-to-back flexible DC converter station start-up circuit. The start-up circuit area and the valve hall area are separated by the valve hall through-wall bushing. The electrical equipment configuration includes, in sequence: through-wall bushing (17-18), post insulator (3-4), bridge arm reactor (1-2), reactor surge arrester (5-6), bypass disconnect switch (7), post insulator (8), circuit current measuring device (9), branch current measuring device (10), start-up resistor (11), voltage measuring device (12), HGIS high voltage switchgear (13), start-up circuit surge arrester (14), post insulator (15), and cross-circuit busbar (16).

[0027] The following is combined Figure 1 Detailed description of the connection structure of the starting circuit: The starting circuit of this embodiment corresponds to a supported reactor. Each unit's starting circuit includes 6 reactors. Figure 1 Taking the starting circuit of two units as an example, the two adjacent reactors are in phase sequence. The equipment connection of the starting circuit of each phase is similar. The specific positioning is adjusted according to the position of the connected flexible DC transformer bushing, which will not be explained in detail here.

[0028] The starting circuit arranged in the semi-indoor area includes several sets of bridge arm reactors, including a first bridge arm reactor (1) and a second bridge arm reactor (2) operating in parallel; one side of the first bridge arm reactor (1) is connected to the through-wall bushing (17) of the valve hall through a post insulator (3), and the other side of the first bridge arm reactor (1) is connected to the bypass disconnector (7); one side of the second bridge arm reactor (2) is connected to the through-wall bushing (18) of the valve hall through a post insulator (4), and the other side of the second bridge arm reactor (2) is connected to the starting resistor (11) through a post insulator (8); the starting resistor (11) and the branch current The measuring device (10) is connected in series, and the starting resistor (11) is connected in parallel with the bypass disconnect switch (7) and then connected in series with the loop current measuring device (9); the loop current measuring device (9) is connected in series with the voltage measuring device (12), the HGIS high voltage switchgear (13) and the starting loop surge arrester (14). The starting loop surge arrester (14) is connected to the flexible DC transformer bushing of the flexible DC transformer room through the post insulator (15) and the cross-circuit busbar (16). The first bridge arm reactor (1) and the second bridge arm reactor (2) are also connected in parallel with the first reactor surge arrester (5) and the second reactor surge arrester (6).

[0029] pass Figure 1 The floor plan clearly shows the electrical configuration and connections of the starting circuit arranged within the semi-indoor unit. Please refer to [link / reference]. Figure 2 The wiring for the starting circuit area is explained below:

[0030] During startup, the flexible DC transmission system charges the DC-side capacitor from the AC system through diodes in the converter. Due to the large capacitance in the MMC converter, a starting resistor (R0) is connected in series in the circuit to avoid large inrush currents and voltages on the capacitor during charging. When the system starts, charging is first performed through the starting resistor (R0). After DC charging is complete, the bypass disconnect switch (-Q90-Q51) across the resistor is closed to remove it from operation. A high-speed inductor gate gas detector (HGIS) is installed after the parallel branch of the starting resistor (R0) and the bypass disconnect switch (-Q90-Q51). This serves two purposes: firstly, in the event of a DC-side fault, if the AC grid circuit breaker fails, the HGIS quickly disconnects the valve from the AC grid, reducing the fault duration; secondly, it facilitates isolation during equipment maintenance or testing. The reactor (L1 / L2) is connected in parallel with the surge arrester (F1), with one side connected to the inner bushing of the valve hall (Z1 / Z2) and the other side connected to the starting resistor (R0) and the bypass disconnect switch (-Q90-Q51). The starting resistor circuit is connected in series with the branch current measuring device (R2), and the circuit current measuring device (R1) measures the total current through the starting resistor (R0) and the disconnect switch (-Q90-Q51), and then connects it in series with the HGIS and the starting circuit surge arrester.

[0031] To more intuitively illustrate the differences and advantages between the starting circuit of this embodiment and the existing outdoor starting circuit, the connection relationship of the outdoor starting circuit will be explained below, such as... Figure 3 The diagram shown is a schematic of the outdoor layout of the starting circuit:

[0032] The bridge arm reactors (1-2) are connected to the AC through-wall bushings (17-18) of the valve hall. The adjacent reactors (1-2) are in phase sequence. The bridge arm reactors (1-2) are connected to the starting resistor (11) and the bypass disconnect switch (7), and then connected to the flexible DC transformer through the HGIS (13) and the starting circuit surge arrester (14). At the node after the bypass disconnect switch (7) and the starting resistor (11) are connected in parallel, there is a voltage measuring device (12) and a circuit current measuring device (9). The starting resistor circuit is also equipped with a branch current measuring device (10). Among them, (19-21) in the figure are all post insulators.

[0033] Please see Figure 4 The cross-sectional view of the outdoor layout of the starting circuit shown is provided. The specific electrical equipment will not be described one by one. It should be noted that since the bypass disconnect switch 7 and the starting resistor 11, the voltage measuring device 12 and the post insulator 21, and the starting circuit surge arrester 14 and the post insulator 15 are arranged in a straight line and are visually overlapping, the bypass disconnect switch 7, the voltage measuring device 12 and the post insulator 15 are not shown in the cross-sectional view.

[0034] It is evident that outdoor-mounted starting circuits generate significant noise from reactors during operation, requiring stringent noise reduction measures. Furthermore, reactors are typically located in the center of the station area, with connected equipment on both sides, resulting in substantial heat generation during operation. Installing sound barriers is difficult and has limited effectiveness, making noise reduction challenging. Additionally, the starting circuit area is tall and occupies a large area, severely impacting the surrounding environment for residents when outdoors. Therefore, this invention proposes a semi-indoor starting circuit design to reduce the noise and sensory impact of the converter station on the surrounding environment. However, in a semi-indoor arrangement, the strong magnetic field of the bridge arm reactor can create eddy currents and generate heat in nearby metal surfaces. Therefore, the heating effect of the bridge arm reactor on surrounding metal surfaces must be fully considered. Moreover, to reduce civil engineering investment, the size of the starting circuit should be minimized. Therefore, in conjunction with… Figure 1 and Figure 5 The plan view and cross-sectional view of the semi-indoor arrangement of the starter circuit shown below provide a detailed description of the semi-indoor arrangement of the starter circuit in this embodiment:

[0035] The equipment in the starting circuit area is arranged in a semi-indoor manner. A steel structure column is set on one side near the post insulator (15), while the other three sides are arranged with walls and wall tops. Since there is no wall on one side, natural convection ventilation of the bridge arm reactor can be realized, which effectively reduces the noise of the fan and air conditioner. At the same time, the starting circuit equipment is basically not visible from the exterior of the building, realizing an environmentally friendly layout.

[0036] The bridge arm reactors (1-2) are dry-type air-core reactors, connected to the valve hall bushings (17-18) via busbars. The incoming bypass disconnect switch (7) and the starting resistor (11) are arranged side by side, making full use of the space in the width direction and saving the longitudinal dimension. The starting resistor branch current measuring device (10) is arranged between the bypass disconnect switch (7) and the starting resistor (11). The loop current measuring device (9) and HGIS (13) are arranged in a straight line. The voltage measuring device (12) and the starting circuit surge arrester (14) are arranged on the side, connected to the flexible DC transformer bushing via the post insulator (15) and the cross-circuit busbar (16). The layout makes full use of the plane space, the equipment of the single-phase starting circuit occupies as squarely as possible, and the equipment is arranged neatly. The reserved space between the bridge arm reactor and the valve hall through-wall bushing is mainly used for the transportation and hoisting of the bridge arm reactor and bushing. Among them, since the bypass disconnect switch (7) and the starting resistor (11), the circuit current measuring device (9) and the HGIS high-voltage switchgear (13), as well as the voltage measuring device (12) and the starting circuit surge arrester (14) are all arranged in a straight line and visually overlap, therefore in Figure 4 The bypass disconnect switch (7), loop current measuring device (9), and voltage measuring device (12) are not shown in the diagram.

[0037] When the starting circuit is arranged outdoors, the starting resistor branch current measuring device (10) is arranged on one side and connected to the starting resistor (11). The voltage measuring device (12), HGIS (13) and starting circuit surge arrester (14) are arranged in a straight line. The HGIS (13), starting circuit surge arrester (14) and insulator (15) basically fill the length of the starting circuit.

[0038] In this embodiment, the starting circuit is arranged in a semi-indoor configuration. The starting resistor branch current measuring device (10) is arranged between the disconnecting switch (7) and the starting resistor (11), which effectively shortens the width dimension. The HGIS (13) and the circuit current measuring device (9) are arranged in a straight line. The voltage measuring device (12) and the starting circuit surge arrester (14) are arranged in a gap, occupying only half of the space in the length direction of the starting circuit. Compared with the outdoor configuration, the space occupied is significantly reduced.

[0039] Because the semi-indoor layout includes steel structure columns, the large-capacity AC dry-type air-core reactor generates a strong alternating magnetic field during operation. Metal structural components (such as reinforcing bars and steel structures) within a certain area of ​​this alternating magnetic field will experience eddy current losses, leading to abnormal heating. Therefore, the steel structure should be arranged as far away from the reactor center as possible. According to the "Construction and Acceptance Specification for Dry-Type Smoothing Reactors in ±800kV and Below Converter Stations" (GB 50774-2012), 5.6.1 a magnetic closed loop should not be formed within a range of twice the reactor body diameter from the reactor body center, with a certain margin considered. Therefore, in this embodiment, the minimum distance from the steel structure column to the reactor body center is set to approximately 2.6 times the reactor body diameter, which is greater than the specification requirement. Furthermore, based on the actual layout dimensions of the project, modeling and magnetic field calculations were performed on various steel structures closest to the reactor center: rectangular lattice columns, four-limb lattice columns, two-limb lattice columns, and metal walls. The simulated temperature rise distribution results show a temperature rise of no more than 6.757K. Simultaneously, physical prototypes of the steel structure were fabricated, and temperature rise tests were conducted on various steel structures closest to the center of the reactor, based on the actual layout dimensions of the project. The test results were close to the simulation results, with a small temperature rise, less than 0.9K. Therefore, in this embodiment, the bridge arm reactor will not cause overheating of surrounding metal structural components. It should be understood that the distance between the steel structure column and the reactor in this embodiment is not limited; this embodiment is merely a preferred distance to reduce the footprint, and can be flexibly set according to actual conditions.

[0040] It should be noted that for large-capacity reactors, due to their large weight, high support, and high center, the foundation must be reinforced with reinforcing steel. The magnetic lines of force generated by the hollow reactor form a closed magnetic circuit within the reactor coil, arranged in an inner-upper-outer-lower-inner space. When these magnetic lines of force pass through the plane of closed reinforcing steel loops (horizontal and vertical loops) within the foundation, a circulating current is generated in each loop. To solve the problem of circulating current in the reinforcing steel, it should be clearly understood that a broken loop in the reinforcing steel breaks the current loop. High-strength enameled wire or insulating binding tape can be used for binding. Simultaneously, insulating materials (insulating flexible tubing) are needed to isolate the rebar joints to cut off the circulating current. Furthermore, interlacing reinforcing steel in the foundation around the bridge arm reactor should be avoided as much as possible. If interlacing cannot be avoided, insulating materials can be used to isolate the rebar joints.

[0041] For actual engineering equipment, the magnetic field calculation results under various current conditions can be analyzed according to the rated current of the reactor and the specifications. The results are then analyzed to determine if they meet the requirements of DL / T "Electromagnetic Environment Limits for ±800kV UHVDC Converter Stations," which states that "the DC magnetic flux density at 1.5m above the ground should not exceed 400mT." To meet the requirements of DL799.7-2010 "Technical Specification for Occupational Environment Monitoring in the Power Industry Part 7: Monitoring of Power Frequency Electric and Magnetic Fields" and the ICNIRP guidelines, the magnetic flux density at a distance of 7.5m from the reactor axis at 50Hz current should be ≤0.5mT. Based on the equipment parameters of the project, to meet the relevant specifications, a fence is installed around the reactor, with the fence at a distance of no less than 7.5m from the reactor axis. In other words, the magnetic field calculation based on the current confirms whether a fence is necessary, and the calculation results show that the semi-indoor arrangement of the starting circuit in this implementation meets the relevant specifications. The specific calculation and analysis process will not be detailed here.

[0042] Since the starting circuit adopts a semi-indoor layout, the arrangement is mainly determined by the external dimensions of the main equipment, the distance requirements between the reactors and other equipment, the distance requirements between the reactors and metal components, the indoor hoisting distance requirements for the reactors, the air clearance requirements, and the maintenance space requirements. The height of the starting circuit is mainly determined by the hoisting height. The longitudinal dimensions of the reactor room are comprehensively determined by the external dimensions of the main equipment, the equipment layout, the electrical clearance requirements, the distance requirements between the reactors and other equipment, the distance requirements between the reactors and metal components, and the equipment hoisting, maintenance, and repair space requirements. The transverse dimensions of the reactor room are comprehensively determined by the spacing between the bridge arm reactors, the distance requirements between the bridge arm reactors and metal components, the electrical clearance requirements, and the maintenance space requirements. The transverse dimensions depend on the reactor spacing, the clearance between the reactors adjacent to the side wall and the side wall, and the distance requirements between the reactors and metal components. Specific dimensions need to be determined comprehensively based on the actual situation and will not be described in detail here.

[0043] In summary, the present invention provides a semi-indoor back-to-back flexible DC converter station start-up circuit. The start-up circuit includes several sets of bridge arm reactors, each including a first bridge arm reactor and a second bridge arm reactor operating in parallel. One side of the first bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side is connected to a bypass disconnect switch. One side of the second bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side is connected to a start-up resistor via a post insulator. The start-up resistor is connected in series with a branch current measuring device, and the start-up resistor is connected in parallel with the bypass disconnect switch and then connected in series with the loop current measuring device. The loop current measuring device is sequentially connected in series with a voltage measuring device, an HGIS high-voltage switchgear, and a start-up circuit surge arrester. The start-up circuit surge arrester is connected to the flexible DC transformer bushing in the flexible DC transformer room via a post insulator and a cross-circuit busbar. The starting circuit of this invention is semi-indoor, with one side open, and the outdoor area is adjacent to the flexible DC transformer room, blocking noise propagation and effectively reducing the noise impact of the reactor on station personnel and the surrounding environment. Simulation results show that the noise contribution value at sensitive points is reduced by 10-19 dB compared to the outdoor arrangement scheme, and the perceptual impact of exposed equipment on residents around the station site is reduced, conforming to the design concept of an environmentally friendly converter station. The semi-indoor reactor arrangement eliminates the risk of rain exposure, and the equipment does not require rain covers, saving equipment costs. It also avoids exposing the surface of the dry-type air-core reactor coils to sunlight, slowing down the aging of the reactor surface protective layer, and effectively reducing the accumulation of dirt on the external insulation of the equipment, reducing the impact of dust and the external environment on the equipment, which is beneficial to the operation and maintenance of the equipment. Furthermore, the semi-indoor arrangement of the starting circuit forms a natural barrier; the flexible DC transformer is arranged in a straight line on the side of the starting circuit, reducing the noise propagation of the flexible DC transformer.

[0044] The various embodiments in this specification are described in a progressive manner. For directly identical or similar parts of the various embodiments, refer to each other. Each embodiment focuses on its differences from other embodiments. It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as these combinations of technical features do not contradict each other, they should be considered within the scope of this specification.

[0045] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A semi-indoor arranged back-to-back HVDC converter station start-up circuit, characterized in that, include: Several groups of bridge arm reactors, wherein the bridge arm reactors include a first bridge arm reactor and a second bridge arm reactor operating in parallel; One side of the first bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side of the first bridge arm reactor is connected to a bypass disconnect switch; One side of the second bridge arm reactor is connected to the through-wall bushing of the valve hall via a post insulator, and the other side of the second bridge arm reactor is connected to the starting resistor via a post insulator. The starting resistor is connected in series with the branch current measuring device, and the starting resistor is connected in parallel with the bypass disconnect switch and then connected in series with the loop current measuring device. The circuit current measuring device is connected in series with the voltage measuring device, the HGIS high-voltage switchgear and the starting circuit surge arrester. The starting circuit surge arrester is connected to the flexible DC transformer bushing in the flexible DC transformer room through the post insulator and the cross-circuit busbar. A steel structure column is arranged on the side of the bridge arm reactor facing the start-up circuit surge arrester, and walls are arranged on the other three sides of the bridge arm reactor, with a wall top arranged above the walls.

2. The semi-indoor arranged back-to-back HVDC station start-up circuit according to claim 1, characterized in that, The first bridge arm reactor and the second bridge arm reactor are in phase sequence, and the first bridge arm reactor and the second bridge arm reactor are respectively connected in parallel with a first reactor surge arrester and a second reactor surge arrester.

3. The semi-indoor arranged back-to-back HVDC station start-up circuit according to claim 1, characterized in that, The bypass disconnect switch and the starting resistor are arranged side by side, and the branch current measuring device is arranged between the bypass disconnect switch and the starting resistor.

4. The semi-in-door arranged back-to-back HVDC station start-up circuit according to claim 3, characterized in that, The circuit current measuring device is arranged side by side with the HGIS high-voltage switchgear, and the voltage measuring device and the starting circuit surge arrester are respectively arranged on both sides of the HGIS high-voltage switchgear.

5. The semi-in-door arranged back-to-back HVDC station start-up circuit according to claim 4, characterized in that, The voltage measuring device and the starting circuit surge arrester are arranged side by side, and the voltage measuring device and the starting circuit surge arrester are arranged in parallel with the HGIS high-voltage switchgear.

6. The start-up circuit of the semi-indoor back-to-back flexible DC converter station according to claim 1, characterized in that, The minimum distance from the steel structure column to the center of the bridge arm reactor is a preset multiple of the diameter of the bridge arm reactor.

7. The semi-indoor arranged back-to-back HVDC station start-up circuit according to claim 1, characterized in that, The bridge arm reactor is a dry-type air-core reactor.

8. The semi-indoor arranged back-to-back HVDC station start-up circuit according to claim 6, characterized in that, The preset multiple is 2.6 times.

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