CN118174246A - A switchable flexible DC connection variable arrangement structure - Google Patents

Abstract

The invention discloses a switching type flexible direct current connection variable arrangement structure in the technical field of flexible direct current transmission, which comprises a working connection transformer, a network side overline switching framework, a network side GIS and a starting loop distribution device, wherein the network side GIS is connected with the working connection transformer through a network side incoming line equipment lead-in wire and a working connection variable network side overline; a valve side loop switching framework is arranged between the working connection transformer and the loop distribution device, and a valve side loop switching bus for connecting the starting loop distribution device with the working connection transformer and the standby connection transformer in an indirect manner is suspended on the valve side loop switching framework. The invention can realize the quick switching of the standby connection transformer and has the advantages of high-efficiency and compact occupation, smooth and beautiful connection of each side of power distribution device and extremely small installation engineering quantity.

Description

A switchable flexible DC connection variable arrangement structure

Technical Field

The present invention relates to the technical field of flexible direct current power transmission, and in particular to a switching flexible direct current connection variable arrangement structure.

Background technique

Offshore wind power has the remarkable characteristics of strong wind energy resource stability and high annual utilization hours. In recent years, offshore wind power generation technology has developed rapidly around the world. As the most technically and economically optimal large-scale, long-distance offshore wind power transmission solution, flexible direct current transmission has the advantages of long transmission distance and flexible operation and regulation. It is a hot research topic and an inevitable choice in the current field of new energy transmission.

Taking into account the characteristics of offshore wind farms being far from shore, large in capacity and clustered through flexible DC transmission, the capacity of a single flexible DC converter unit of an onshore converter station (also serving as a centralized control center, hereinafter referred to as a converter station) is gradually increasing, and the capacity of a single connecting transformer is also increasing accordingly. In particular, when the connecting transformer uses three single-phase transformers, once a transformer is shut down due to a fault or planned maintenance, the entire converter unit must be shut down.

Normally, a spare connection transformer is installed in the converter station. When the working connection transformer fails, the conductor fittings on each side of the faulty connection transformer need to be removed first, and the top of the faulty connection transformer needs to be moved to the transport trolley with a jack, and the foundation is dragged out along the track and removed; then the spare connection transformer is also moved to the faulty phase position along the steel track, pushed into the corresponding foundation and put in place. After the faulty connection transformer and the spare connection transformer are moved and put in place, the conductors and fittings on each side of the spare connection transformer need to be restored, and the secondary wiring and debugging work need to be completed. Without considering the influence of adverse factors such as weather, it takes about 15 to 20 days to complete the above work. If the connection transformer is equipped with a soundproof cover (Box-in), this construction period will be extended. During the entire construction period, the flexible direct transmission channel is completely stopped and the large-capacity offshore wind power transmission channel is blocked, which is poor in economic efficiency.

Therefore, how to shorten the replacement time of the standby connection transformer in the converter station has become a technical problem that needs to be solved urgently by those skilled in the art.

Summary of the invention

In view of this, an object of the present invention is to provide a switching flexible DC connection transformer arrangement structure to solve the technical problem that it takes a long time to replace the standby connection transformer in the existing converter station.

The technical solution adopted by the present invention is: a switching flexible DC connection variable arrangement structure, comprising:

A working connection transformer, three of which are arranged longitudinally;

A standby connection transformer, which is arranged at one end of the arrangement direction of the working connection transformers;

A grid-side GIS, wherein the grid-side GIS is arranged on one side of the working connection transformer, and a standby connection transformer grid-side crossover line is connected between the grid-side GIS and the standby connection transformer;

A grid-side cross-line switching framework, the grid-side cross-line switching framework is arranged between the grid-side GIS and the working connection transformer, and the grid-side cross-line switching framework is provided with a grid-side cross-line switching busbar electrically connected to the standby connection transformer grid-side cross-line; a working connection transformer grid-side cross-line is connected between the grid-side cross-line switching framework and the working connection transformer, the working connection transformer grid-side cross-line is electrically connected to the grid-side GIS through a grid-side incoming line device lead-in line, and the grid-side incoming line device lead-in line can be disconnected from the working connection transformer grid-side cross-line and electrically connected to the grid-side cross-line switching busbar;

A starting circuit power distribution device, the starting circuit power distribution device is arranged on the other side of the working connection transformer;

A valve-side circuit switching frame is provided between the starting circuit power distribution device and the working connection transformer, and the valve-side circuit switching frame is provided with three valve-side circuit switching busbars electrically connected to the starting circuit power distribution device, the working connection transformer is electrically connected to two valve-side circuit switching busbars through the valve-side bushing lead-out line, and the standby connection transformer can be electrically connected to any two valve-side circuit switching busbars through the valve-side bushing lead-out line.

Preferably, the starting circuit power distribution device is arranged below the valve side circuit switching bus.

Preferably, the grid-side GIS is provided with a hanging point cooperating with the standby connection variable grid-side spanning line.

Preferably, a transition tube busbar installed on the ground is electrically connected between the standby connection transformer grid-side span and the grid-side span switching busbar.

Preferably, the grid-side GIS and the grid-side cross-line switching frame are located on one side of the transportation road, the working connection transformer, the standby connection transformer, the valve-side loop switching frame and the starting loop power distribution device are located on the other side of the transportation road, and the working connection transformer grid-side cross-line and the standby connection transformer grid-side cross-line use overhead soft wires to cross the transportation road.

Preferably, a supporting insulator is provided below the valve-side loop switching busbar.

Beneficial effects of the present invention:

The present invention adopts a switching structure instead of a replacement structure, installs a standby connection transformer at one end of the arrangement direction of the three working connection transformers, arranges a grid-side cross-line switching frame between the working connection transformer and the grid-side GIS, and arranges a valve-side loop switching frame between the working connection transformer and the starting loop power distribution device; a grid-side cross-line switching busbar is installed on the grid-side cross-line switching frame, and the grid-side cross-line switching busbar is electrically connected to the standby connection transformer through the standby connection transformer grid-side cross-line; a valve-side loop switching busbar electrically connected to the starting loop power distribution device is installed on the valve-side loop switching frame, and the valve-side loop switching busbar electrically connected to the starting loop power distribution device is installed on the valve-side loop switching frame. The switching bus is electrically connected to the working connection transformer through the valve side bushing lead-out line; when a single working connection transformer fails, the connection between the faulty connection transformer and the grid-side incoming line equipment lead-in line and the valve-side loop switching bus can be disconnected, and the faulty connection transformer can be quickly disconnected and the standby connection transformer can be connected through the electrical connection between the grid-side incoming line equipment lead-in line and the grid-side cross-line switching bus, and the standby connection transformer and the valve-side loop switching bus. This not only shortens the replacement time of the standby connection transformer, reduces the economic losses caused by power outages, but also reduces the workload and work intensity of the staff.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of the switchable flexible DC connection transformer arrangement structure of the present invention before the standby connection transformer is put into use;

FIG2 is a schematic structural diagram of the switchable flexible DC connection transformer arrangement structure of the present invention after the standby connection transformer is put into operation.

Description of reference numerals in the figures:

1. Working connection transformer; 2. Standby connection transformer; 3. Grid-side GIS; 4. Standby connection transformer grid-side crossover line; 5. Grid-side crossover line switching frame; 6. Grid-side crossover line switching busbar; 7. Working connection transformer grid-side crossover line; 8. Grid-side incoming line equipment lead-in line; 9. Starting circuit distribution device; 10. Valve-side circuit switching frame; 11. Valve-side circuit switching busbar; 12. Valve-side bushing lead-out line; 13. Transition pipe busbar; 14. Support insulator.

Detailed ways

The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. These embodiments are only used to illustrate the present invention, but not to limit the present invention.

In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Furthermore, in the description of the present invention, unless otherwise specified, “plurality” means two or more.

In the embodiment, as shown in FIG. 1 and FIG. 2 , a switching flexible DC connection variable arrangement structure comprises:

The working connection transformer 1, three working connection transformers 1 are arranged at intervals along the longitudinal direction.

A standby connection transformer 2 is provided at one end of the arrangement direction of the working connection transformer 1 .

The grid-side GIS 3 is arranged on one side of the working connection transformer 1 in a lateral direction, and a standby connection transformer grid-side crossover line 4 is connected between the grid-side GIS 3 and the standby connection transformer 2 .

A grid-side cross-line switching framework 5 is provided between the grid-side GIS 3 and the working connection transformer 1, and a grid-side cross-line switching busbar 6 is installed on the grid-side cross-line switching framework 5, and the grid-side cross-line switching busbar 6 is electrically connected to the standby connection transformer grid-side cross-line 4; a working connection transformer grid-side cross-line 7 is connected between the grid-side cross-line switching framework 5 and the working connection transformer 1, and the working connection transformer grid-side cross-line 7 is electrically connected to the grid-side GIS 3 through a grid-side incoming line device lead-in line 8, and the grid-side incoming line device lead-in line 8 can be disconnected from the working connection transformer grid-side cross-line 7 and electrically connected to the grid-side cross-line switching busbar 6.

A starting circuit power distribution device 9 is arranged on the other side of the working connection transformer 1 in the lateral direction.

The valve side circuit switching frame 10 is arranged between the starting circuit power distribution device 9 and the working connection transformer 1, and three valve side circuit switching busbars 11 electrically connected to the starting circuit power distribution device 9 are installed on the valve side circuit switching frame 10. The working connection transformer 1 is electrically connected to two valve side circuit switching busbars 11 through the valve side bushing lead-out line 12, and the standby connection transformer 2 can be electrically connected to any two valve side circuit switching busbars 11 through the valve side bushing lead-out line 12.

The present application adopts a switching structure instead of a replacement structure, installs the standby connection transformer 2 at one end of the arrangement direction of the three working connection transformers 1, arranges a grid-side cross-line switching frame 5 between the working connection transformer 1 and the grid-side GIS 3, and arranges a valve-side loop switching frame 10 between the working connection transformer 1 and the starting loop power distribution device 9; a grid-side cross-line switching bus 6 is installed on the grid-side cross-line switching frame 5, and the grid-side cross-line switching bus 6 is electrically connected to the standby connection transformer 2 through the standby connection transformer grid-side cross-line 4; a valve-side loop switching bus 11 electrically connected to the starting loop power distribution device 9 is installed on the valve-side loop switching frame 10, and the valve-side loop switching bus 11 is electrically connected to the working connection transformer 1 through the valve-side bushing lead-out line 12; when When a single working connecting transformer 1 fails, the faulty connecting transformer can be disconnected from the grid-side incoming line equipment lead-in line 8 and the valve-side loop switching bus 11, and the grid-side incoming line equipment lead-in line 8 is electrically connected to the grid-side cross-line switching bus 6, and the standby connecting transformer 2 is electrically connected to the valve-side loop switching bus 11. The faulty connecting transformer can be quickly disconnected and the standby connecting transformer 2 can be connected to the grid. This not only shortens the replacement time of the standby connecting transformer 2, reduces the economic losses caused by power outages, but also reduces the workload and work intensity of the staff.

Specific embodiments, as shown in FIG1 and FIG2, a switchable flexible DC connection transformer arrangement structure includes: a working connection transformer 1, a standby connection transformer 2, a grid-side GIS 3, a standby connection transformer grid-side span 4, a grid-side span switching frame 5, a grid-side span switching bus 6, a working connection transformer grid-side span 7, a grid-side incoming line equipment lead-in line 8, a start-up circuit distribution device 9, a valve-side circuit switching frame 10, a valve-side circuit switching bus 11 and a valve-side casing lead-out line 12; wherein,

The number of the working connection transformers 1 is three, namely connection transformer A phase, connection transformer B phase and connection transformer C phase, and the three working connection transformers 1 are arranged at intervals along the longitudinal direction; the standby connection transformer 2 is installed at one end of the arrangement direction of the working connection transformers 1.

Specifically, the working connecting transformer 1 and the standby connecting transformer 2 are single-phase double-winding transformers with a winding type of Ynd11. There are three working connecting transformers 1 and one standby connecting transformer 2. The four connecting transformers are arranged in a straight line on the right side of the transport road, and a firewall is used to separate two adjacent connecting transformers.

The grid-side GIS 3 is arranged on one side of the working connection transformer 1 and on the left side of the transportation road, and a standby connection transformer grid-side crossover line 4 is connected between the grid-side GIS 3 and the standby connection transformer 2 .

Specifically, the grid-side GIS 3 is arranged indoors in the grid-side GIS room, i.e., the AC field of the converter station, and is equipped with switch busbars and other equipment. The GIL busbar is used to lead the equipment compartment of the corresponding connection transformer out of the GIS room, facing the incoming line direction of the connection transformer; the grid-side incoming line equipment includes capacitive voltage transformers, lightning arresters, etc., and open equipment is used. A hanging point is set on the outdoor wall beam of the GIS room, one end of the standby connection transformer grid-side span 4 is connected to the grid-side bushing of the standby connection transformer 2, and the other end of the standby connection transformer grid-side span 4 is fixedly connected to the GIS outdoor hanging point, so that the standby connection transformer grid-side span 4 is suspended above the transportation road; in this way, the dedicated frame used in conjunction with the standby connection transformer grid-side span 4 can be reduced, and the frame engineering volume can be optimized.

The grid-side cross-line switching frame 5 is arranged between the grid-side GIS 3 and the working connection transformer 1, and a grid-side cross-line switching busbar 6 is installed on the grid-side cross-line switching frame 5, one end of which is electrically connected to the standby connection transformer grid-side cross-line 4; a working connection transformer grid-side cross-line 7 is connected between the grid-side cross-line switching frame 5 and the working connection transformer 1, and the working connection transformer grid-side cross-line 7 is electrically connected to the grid-side GIS 3 through a grid-side incoming line device lead-in line 8, and the grid-side incoming line device lead-in line 8 can be disconnected from the working connection transformer grid-side cross-line 7 and electrically connected to the grid-side cross-line switching busbar 6.

Specifically, the grid-side crossover switching frame 5 is composed of three frames to form a C-shaped combined frame, one of which is provided with a hanging point that matches the working connection transformer grid-side crossover 7, and the other two frames are provided with hanging points that match the grid-side crossover switching busbar 6; the grid-side crossover switching busbar 6 is suspended on the grid-side crossover switching frame 5 along the arrangement direction of the three working connection transformers 1; the working connection transformer grid-side crossover 7 is suspended between the grid-side crossover switching frame 5 and the working connection transformer 1, and the number of the working connection transformer grid-side crossover 7 is three, and one end of the three working connection transformer grid-side crossovers 7 is fixedly connected to the grid-side bushings of the three working connection transformers 1 in a one-to-one correspondence, and the other end is fixedly connected to the hanging point on the grid-side crossover switching frame 5.

The grid-side incoming line equipment of the grid-side GIS 3 is arranged below the grid-side cross-line switching frame 5, and the grid-side incoming line equipment of the grid-side GIS 3 is connected one-to-one with three working connection transformer grid-side cross-lines 7 through three grid-side incoming line equipment lead-in lines 8. Each grid-side incoming line equipment lead-in line 8 can be disconnected from the working connection transformer grid-side cross-line 7 and be led up to be electrically connected to the grid-side cross-line switching busbar 6.

The starting circuit power distribution device 9 is arranged on the other side of the working connection transformer 1, and the number of the starting circuit power distribution device 9 is three groups and connected to the valve hall. Each group of the starting circuit power distribution device 9 includes a valve side lightning arrester, a valve side grounding switch, a voltage transformer, a valve side circuit breaker, a starting resistor, an isolating switch and a current measuring device, etc., and an open type device is adopted.

The valve side circuit switching frame 10 is arranged between the starting circuit power distribution device 9 and the working connection transformer 1, and three valve side circuit switching busbars 11 electrically connected to the starting circuit power distribution device 9 are installed on the valve side circuit switching frame 10. The working connection transformer 1 is electrically connected to the two valve side circuit switching busbars 11 through the valve side bushing lead-out line 12, and the standby connection transformer 2 can be electrically connected to any two valve side circuit switching busbars 11 through the valve side bushing lead-out line 12.

Specifically, the valve side circuit switching frame 10 is composed of 6 frames to form a C-shaped combined frame, among which 4 continuous frames are supported on the firewall connected to the transformer and are provided with hanging points matching the working connection transformer side span line 7, and the other 2 frames are provided with hanging points matching the valve side circuit switching busbar 11, and the three valve side circuit switching busbars 11 are suspended and arranged at laterally intervals on the valve side circuit switching frame 10, and the three sets of starting circuit distribution devices 9 are electrically connected to the three valve side circuit switching busbars 11 one by one.

Preferably, in this embodiment, the valve side circuit switching frame 10 and the connecting transformer frame are combined and arranged above the connecting transformer; the valve side lightning arrester, valve side grounding switch, starting circuit voltage transformer, supporting insulator, etc. of the starting circuit power distribution device are arranged below the valve side circuit switching bus 11 while meeting the live distance, so that the space utilization rate of the connecting transformer and the power distribution devices on each side is high, the layout is compact and reasonable, and the overall size requirements, especially the size of the valve side power distribution device, are not increased. On the basis of significantly shortening the replacement time of the faulty connecting transformer, compared with the traditional solution of transporting the spare connecting transformer, the occupied area is basically the same, and it has good technical and economic performance and strong feasibility, which indirectly improves the availability and overall economy of the flexible DC transmission system.

Preferably, in the present embodiment, a transition tube busbar 13 is electrically connected between the standby connection transformer grid-side span 4 and the grid-side span switching busbar 6. The transition tube busbar 13 is arranged with ground support, one end of the transition tube busbar 13 is located below the grid-side span switching busbar 6, and the other end of the transition tube busbar 13 extends to below the standby connection transformer grid-side span 4, serving as a connecting conductor between the grid-side span switching busbar 6 and the standby connection transformer grid-side span 4.

Preferably, in this embodiment, the grid-side GIS 3 (grid-side GIS and its grid-side incoming line equipment), the grid-side cross-line switching frame 5 and the grid-side cross-line switching bus 6 are located on one side of the transportation road, and the working connection transformer 1, the standby connection transformer 2, the valve-side loop switching frame 10, the valve-side loop switching bus 11 and the starting loop distribution device 9 are located on the other side of the transportation road, and the working connection transformer grid-side cross-line 7 and the standby connection transformer grid-side cross-line 4 use overhead soft wires to cross the transportation road.

In this embodiment, a support insulator 14 is provided below the valve-side loop switching busbar 11, that is, four support insulators 14 are provided below the valve-side loop switching busbar 11 at the valve-side bushing position directly opposite the standby connection transformer 2, so as to flexibly realize the standby connection transformer 2 being put into operation as any one of the three phases A/B/C.

The working process of the switchable flexible DC connection transformer arrangement structure of the present application is as follows:

As shown in Figure 1, the valve-side bushings of the three working connection transformers are: a, y (corresponding to connection transformer phase A), b, z (corresponding to connection transformer phase B), c, x (corresponding to connection transformer phase C). The valve-side bushings are connected to the three suspended valve-side circuit switching busbars outside the connection transformer end to end in sequence through soft wire outlets, forming a connection sequence of a-y-b-z-c-x.

As shown in Figure 1, when the three working connection transformers are operating normally, the grid-side GIS, grid-side incoming line equipment lead-in line, working connection transformer grid-side crossover line, and working connection transformer are interconnected in sequence with soft wires, all of which are energized; the grid-side crossover line switching bus, transition tube bus, standby connection grid-side crossover line, and standby connection transformer are interconnected with soft wires, but all of them are not energized. At this time, the complete circuit connection relationship is: the grid-side incoming line equipment of the grid-side GIS is interconnected with soft wires and led up to the grid-side crossover line switching frame through the grid-side incoming line equipment lead-in line, and then connected to the working connection transformer grid-side crossover line through a jumper. The working connection transformer grid-side crossover line crosses the transportation road and is led down to the grid-side bushing of the working connection transformer; each single-phase working connection transformer has two valve-side bushings, which are led out through the valve-side bushing lead-out line (soft wire) and connected to the suspended valve-side loop switching bus.

As shown in Figure 2, if the A-phase working connection transformer fails, it is necessary to remove the grid-side incoming line equipment lead-in line corresponding to the A-phase working connection transformer, and install the disconnected grid-side incoming line equipment lead-in line to the grid-side cross-line switching busbar suspended on the grid-side cross-line switching frame; remove the valve-side bushing lead-out line corresponding to the A-phase working connection transformer, and install the valve-side bushing lead-out line between the standby connection transformer and the valve-side loop switching busbar. The entire standby connection transformer switching process only requires the removal of 3-span equipment connections and the installation of 3-span equipment connections. The related engineering volume is greatly reduced compared to the traditional standby connection transformer replacement solution, effectively reducing the amount of work and shortening the construction period.

Compared with the prior art, this application has at least the following beneficial technical effects:

1. When a working connecting transformer fails and stops operating, on-site installers do not need to use the traditional method to transport and replace the faulty connecting transformer and the spare connecting transformer, which significantly shortens the power outage duration of the flexible DC system caused by the replacement of the connecting transformer under the traditional method, and effectively reduces the economic losses caused by the power outage.

2. Compared with the existing layout structure, the overall connection relationship of the distribution equipment in the converter station is simple. Some of the wires required for switching the standby connection transformer, such as those with relatively high height and relatively long span, are built at one time during the new construction. When the standby connection transformer is put into operation for reconnection, it is only necessary to remove and install several soft wires to complete the commissioning of the standby connection transformer, which significantly optimizes the engineering workload of the on-site connection transformer-related distribution equipment reconnection work and further shortens the power outage duration.

3. The overall size of the converter station area has not been increased due to the installation of the valve-side circuit switching structure, and the area occupied is basically the same as that of the traditional solution. The overall technical and economic performance of the solution is good.

4. This application can realize the rapid switching of the standby connection transformer, and has the advantages of efficient and compact space, smooth and beautiful connection of the distribution devices on each side, and extremely small installation work.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims (6)

1. A switchable flexible DC connection variable arrangement structure, characterized by comprising: A working connection transformer (1), three of the working connection transformers (1) are arranged longitudinally; A standby connection transformer (2), wherein the standby connection transformer (2) is arranged at one end of the arrangement direction of the working connection transformer (1); A grid-side GIS (3), the grid-side GIS (3) being arranged on a horizontal side of the working connection transformer (1), and a standby connection transformer grid-side crossover line (4) being connected between the grid-side GIS (3) and the standby connection transformer (2); A grid-side cross-line switching frame (5), the grid-side cross-line switching frame (5) being arranged between a grid-side GIS (3) and a working connection transformer (1), and the grid-side cross-line switching frame (5) being provided with a grid-side cross-line switching busbar (6) electrically connected to a standby connection transformer grid-side cross-line (4); a working connection transformer grid-side cross-line (7) being connected between the grid-side cross-line switching frame (5) and the working connection transformer (1), the working connection transformer grid-side cross-line (7) being electrically connected to the grid-side GIS (3) via a grid-side incoming line device lead-in line (8), and the grid-side incoming line device lead-in line (8) being able to be disconnected from the working connection transformer grid-side cross-line (7) and electrically connected to the grid-side cross-line switching busbar (6); A starting circuit power distribution device (9), wherein the starting circuit power distribution device (9) is arranged on the other side of the working connection transformer (1) in a lateral direction; A valve side circuit switching frame (10), the valve side circuit switching frame (10) being arranged between a starting circuit power distribution device (9) and a working connection transformer (1), and the valve side circuit switching frame (10) being provided with three valve side circuit switching busbars (11) electrically connected to the starting circuit power distribution device (9), the working connection transformer (1) being electrically connected to two valve side circuit switching busbars (11) via valve side casing lead-out lines (12), and the standby connection transformer (2) being electrically connected to any two valve side circuit switching busbars (11) via valve side casing lead-out lines (12). 2. A switchable flexible DC connection variable arrangement structure according to claim 1, characterized in that the starting circuit power distribution device (9) is arranged below the valve side circuit switching bus (11). 3. A switchable flexible DC connection transformer arrangement structure according to claim 1, characterized in that a hanging point is provided on the grid-side GIS (3) to match the grid-side crossover line (4) of the standby connection transformer. 4. A switchable flexible DC connection transformer arrangement structure according to claim 1, characterized in that a transition tube busbar (13) disposed on the ground is electrically connected between the grid-side span (4) of the standby connection transformer and the grid-side span switching busbar (6). 5. A switchable flexible DC connection transformer arrangement structure according to claim 1, characterized in that the grid-side GIS (3) and the grid-side crossover switching frame (5) are located on one side of the transportation road, the working connection transformer (1), the standby connection transformer (2), the valve-side loop switching frame (10) and the starting loop distribution device (9) are located on the other side of the transportation road, and the working connection transformer grid-side crossover (7) and the standby connection transformer grid-side crossover (4) use overhead soft wires to cross the transportation road. 6. A switchable flexible DC connection transformer arrangement structure according to claim 1, characterized in that a support insulator (14) is provided below the valve side loop switching bus (11).