CN117977669A - Power transmission system of flexible direct current marine converter station sharing metal loop - Google Patents

Abstract

The invention relates to the technical field of offshore wind power, and provides a power transmission system of a flexible direct current offshore converter station sharing metal loop, which comprises: the system comprises a plurality of flexible direct current offshore converter stations, wherein each flexible direct current offshore converter station adopts a symmetrical bipolar wiring structure; the system comprises a plurality of land-based converter stations, a plurality of flexible Direct Current (DC) marine converter stations and a plurality of power lines, wherein each land-based converter station is connected with the corresponding flexible DC marine converter station through a positive pole cable and a negative pole cable; and the total metal loop is divided into a plurality of neutral branch lines, and all the neutral branch lines are connected with all the land converter stations in a one-to-one correspondence manner. The invention can greatly reduce the total cost of the neutral cable, and has half power transmission capability when the direct current side has single-pole fault.

Description

Power transmission system of flexible direct current marine converter station sharing metal loop

Technical Field

The invention relates to the technical field of offshore wind power, in particular to a power transmission system of a flexible direct current offshore converter station sharing a metal loop.

Background

With the large-scale development of offshore wind power in China, the offshore wind power transmission is more and more important, and the investment ratio is also more and more large. The flexible direct current transmission technology is a transmission technology developed in recent years, has the advantages of stable system, mutual decoupling of alternating current and direct current systems, independent control of active and reactive power, flexible adjustment mode, small occupied area and the like, and is particularly suitable for grid-connected power transmission of long-distance and large-capacity deep and open-sea wind power plants. At present, a plurality of land flexible direct current technology demonstration projects are built and put into operation in China, but flexible direct current delivery of the offshore wind farm is still in a starting stage in China.

At present, offshore wind power generation is an emerging industry, development is rapid in recent years, but offshore distance of offshore wind farms in China is generally within 30km at present, so that electric energy of offshore wind power in China is output through alternating current sea cables at present. As offshore wind power is developed to a larger scale and a longer distance, in general, when the offshore distance of the offshore wind farm exceeds 60km, it is obvious that the conventional ac power transmission mode is uneconomical, and a dc power transmission mode suitable for large-capacity and long-distance power transmission should be considered. As the transmission distance is required more and the transmission capacity is required more and more, the dc power transmission will play an important role in the development and utilization of the offshore wind farm by adopting the dc power transmission, and a flexible dc offshore converter station needs to be constructed, which is a device for collecting the electric energy of the offshore wind farm by using an ac line and then converting the electric energy into dc output.

The prior art patent document (application number 202310209366.9) discloses a distributed offshore direct current transmission system, the converter station units of which are essentially a symmetrical monopole system. Although the symmetrical monopole system has less equipment, simple wiring, relatively small size and weight of the offshore platform, no metal loop is needed, and engineering construction investment and difficulty are low. At present, the offshore wind power flexible direct current transmission engineering put into operation at home and abroad adopts a symmetrical monopole wiring mode. However, the symmetrical monopole system has a certain disadvantage in terms of reliability, and any converter or submarine cable fails, which results in the direct current system being completely shut down until the failure is eliminated, during which the power generation of all offshore wind power is lost.

As global offshore wind power development is being advanced from near coast to far coast, flexible direct current transmission systems are increasingly being used in far offshore wind power. Because the flexible direct current transmission system has the characteristics of flexible operation mode and passive operation capability, the flexible direct current transmission becomes a main technical means of offshore wind power grid connection. The problem of fault protection of flexible direct current transmission is also an important focus of current attention because of the long distance of open sea transmission and complex fault conditions. In the prior art, in a flexible direct current transmission system, the transmission distance between a land alternating current power grid and an offshore wind farm is far, when the land alternating current power grid or a land converter station breaks down and a communication signal between the land converter station and the flexible direct current offshore converter station is lost or interrupted, the flexible direct current offshore converter station cannot quickly execute a protection action, the fault cannot be cleared for a long time, and electrical equipment can be damaged due to overlarge fault stress born for a long time.

In addition, in the prior art, each symmetrical bipolar flexible direct current marine converter station and the land-based marine converter station are connected through three kinds of marine cables (a positive pole marine cable, a negative pole marine cable and a neutral line marine cable), and when a plurality of symmetrical bipolar flexible direct current marine converter stations are arranged at the same time, the cost of the marine cables is relatively high.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, the present invention is to provide a power transmission system with a metal loop shared by flexible dc offshore converter stations, which can greatly reduce the overall cost of the neutral-line submarine cable, and still has half power transmission capability when a monopole fault occurs on the dc side, and is particularly suitable for use in a large-capacity offshore wind power transmission scenario which is far from land and is difficult to overhaul.

In order to solve the technical problem, the invention provides a power transmission system of a flexible direct current marine converter station sharing metal loop, comprising:

The system comprises a plurality of flexible direct current offshore converter stations, a plurality of power transmission lines and a plurality of power transmission lines, wherein each flexible direct current offshore converter station adopts a symmetrical bipolar wiring structure so as to still have half power transmission capacity when a monopole fault occurs on a direct current side, one flexible direct current offshore converter station is used as a neutral line collecting station, and neutral line sea cables of the rest flexible direct current offshore converter stations are collected to the neutral line collecting station;

the system comprises a plurality of land-based converter stations, a plurality of flexible direct current marine converter stations and a plurality of power lines, wherein all the land-based converter stations and all the flexible direct current marine converter stations are in one-to-one correspondence, and each land-based converter station and the corresponding flexible direct current marine converter station are respectively connected through a positive pole cable and a negative pole cable;

And the length of the total metal loop is matched with the offshore distance of the neutral line collecting station, two end points of the total metal loop along the extending direction of the total metal loop are respectively a collecting end and a dispersing end, the collecting end of the total metal loop is connected with the neutral line collecting station, the dispersing end of the total metal loop extends to a coastline near one of the land-based converter stations, the dispersing end of the total metal loop is divided into a plurality of neutral branch lines, and all the neutral branch lines are connected with all the land-based converter stations in a one-to-one correspondence.

Further, the dipoles in the symmetrical bipolar wiring structure of the flexible direct current offshore converter station are respectively a pole one and a pole two, the flexible direct current offshore converter station comprises four valve hall units and four direct current field units, a converter valve group or a converter valve tower is arranged in each valve hall unit, a smoothing reactor and an AIS power distribution device are arranged in each direct current field unit, the four valve hall units are respectively an upper bridge arm valve hall of the pole one, an upper bridge arm valve hall of the pole two, a lower bridge arm valve hall of the pole one and a lower bridge arm valve hall of the pole two, and the four direct current field units are respectively an polar direct current field of the pole one, an polar direct current field of the pole two, a neutral line direct current field of the pole one and a neutral line direct current field of the pole two; the flexible direct current offshore converter station further comprises an alternating current field, converter transformer units and station transformer units, wherein alternating current GIS power distribution devices are arranged in the alternating current field and are connected with an offshore wind turbine, and the number of the converter transformer units is four.

Further, the converter transformer unit is connected with a converter valve bank or a converter valve tower of the valve hall unit through a direct-current GIS power distribution device, and the network side of the converter transformer unit is connected with a 66kV offshore wind turbine through a 66kV alternating-current GIS power distribution device.

Further, the flexible direct current offshore converter station adopts an upper bridge arm layered structure, an upper bridge arm valve hall of a first pole, an upper bridge arm valve hall of a second pole, an polar line direct current field of the first pole and an polar line direct current field of the second pole are all located at a first height, a lower bridge arm valve hall of the first pole, a lower bridge arm valve hall of the second pole, a neutral line direct current field of the first pole and a neutral line direct current field of the second pole are all located at a second height, the second height is larger than the first height, the upper bridge arm of the first pole is arranged in the upper bridge arm valve hall of the first pole, the upper bridge arm of the second pole is arranged in the upper bridge arm valve hall of the second pole, the lower bridge arm of the first pole is arranged in the lower bridge arm valve hall of the first pole, and the lower bridge arm of the second pole is arranged in the lower bridge arm valve hall of the second pole; and a plurality of overhauling holes are formed in the top of the neutral line direct current field of the first pole and the top of the neutral line direct current field of the second pole.

Further, the flexible direct current offshore converter station has a seven-layer structure, and a first layer, a second layer, a third layer, a fourth layer, a fifth layer, a sixth layer and a seventh layer are respectively arranged from bottom to top; the first layer is provided with a seawater lifting equipment room, a sodium hypochlorite treatment room and a first auxiliary equipment room; the second layer is provided with a fire pump room, a diesel generator room, a 400V station electricity room, a storage battery room and a second auxiliary equipment room; the third layer is provided with a main control room, a valve cooling equipment room and a third auxiliary equipment room; the fourth layer is provided with a cable layer unit and the bottom of the GIS equipment room; the fifth layer is provided with a GIS equipment room middle part, a converter transformer unit and a station transformer unit; the sixth layer is provided with a GIS equipment room top and a maneuvering room; and the seventh layer is provided with a crane, a helicopter platform and an equipment room access hole.

Further, the upper bridge arm valve hall of the first pole, the upper bridge arm valve hall of the second pole, the polar direct current field of the first pole and the polar direct current field of the second pole occupy the first layer to the third layer; the alternating-current side of the converter valve bank is connected with an alternating-current side current measuring device, the alternating-current side current measuring device is connected with an alternating-current side incoming line sleeve, the direct-current side of the converter valve bank is connected with a direct-current side current measuring device, and the direct-current side current measuring device is connected with a direct-current side outgoing line sleeve; the converter transformer unit enters an upper bridge arm valve hall from the top of the third layer through an alternating current side wire inlet sleeve after being connected with a direct current GIS power distribution device, and the alternating current side wire outlet sleeve of the upper bridge arm is arranged on the upper side of the upper bridge arm valve hall; the direct-current side outlet sleeve of the upper bridge arm is horizontally arranged at the upper side of the valve hall of the upper bridge arm, and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the upper bridge arm valve hall is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester.

Furthermore, the converter valve towers are of a quadruple valve structure, and three converter valve towers form each phase of bridge arm; bridge arm reactors in the direct current field units are connected with a converter valve tower through wall bushings, and the bridge arm reactors are connected to an AIS distribution device after converging through hanging pipe nuts.

Further, the lower bridge arm valve hall of the first pole, the lower bridge arm valve hall of the second pole, the neutral line direct current field of the first pole and the neutral line direct current field of the second pole occupy the fourth layer to the sixth layer; the alternating-current side of the converter valve bank is connected with an alternating-current side current measuring device, the alternating-current side current measuring device is connected with an alternating-current side incoming line sleeve, the direct-current side of the converter valve bank is connected with a direct-current side current measuring device, and the direct-current side current measuring device is connected with a direct-current side outgoing line sleeve; the converter transformer unit enters a lower bridge arm valve hall through an alternating-current side wire inlet sleeve after being connected with a direct-current GIS power distribution device, and the alternating-current side wire outlet sleeve of the lower bridge arm is arranged in the middle of the lower bridge arm valve hall; the direct-current side outlet sleeve of the lower bridge arm is horizontally arranged on the upper side of the valve hall of the lower bridge arm, and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the lower bridge arm valve hall is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester.

Further, the cable of the lower bridge arm directly enters the middle part of the valve hall of the lower bridge arm from the GIS equipment room and through the alternating current side outlet sleeve.

As described above, the power transmission system for the flexible direct current marine converter station sharing metal loop has the following beneficial effects: on the one hand, each flexible direct current offshore converter station adopts a symmetrical bipolar wiring structure, so that when a monopole fault occurs on the direct current side, the flexible direct current offshore converter station still has half power transmission capacity, fault loss is greatly reduced, and the flexible direct current offshore converter station is suitable for being applied to a large-capacity open sea wind power transmission scene which is far away from land and is difficult to overhaul. On the other hand, the flexible direct current offshore converter stations share one total metal loop, specifically, one flexible direct current offshore converter station is used as a neutral line collecting station, and neutral line sea cables of the rest flexible direct current offshore converter stations are collected to the neutral line collecting station; the collecting end of the total metal loop is connected with the neutral line submarine cable of the neutral line collecting station, so that the neutral line submarine cable can be uniformly sent to a coastline near one of the land converter stations through the neutral line collecting station, and finally, the neutral line submarine cable is correspondingly connected with all the land converter stations one by one through all the neutral branch lines. Therefore, the power transmission system can remarkably improve the power supply reliability of the flexible direct current offshore converter station, increase the generating capacity income, simultaneously reduce the length of the neutral cable and remarkably reduce the manufacturing cost of the cable. Therefore, the power transmission system can greatly reduce the overall cost of the neutral line submarine cable, has half power transmission capacity when a monopole fault occurs on the direct current side, and is particularly suitable for large-capacity open sea wind power transmission scenes which are far away from land and difficult to overhaul.

Drawings

Fig. 1 shows a schematic diagram of a power transmission system for a common metal return line of a flexible dc offshore converter station according to the invention.

Fig. 2 shows an end view of a flexible dc offshore converter station.

Fig. 3 shows a floor plan of a first floor of a flexible direct current marine converter station.

Fig. 4 shows a floor plan of the second floor of the flexible dc offshore converter station.

Fig. 5 shows a floor plan of a third layer of a flexible dc offshore converter station.

Fig. 6 shows a floor plan of a fourth floor of the flexible dc offshore converter station.

Fig. 7 shows a floor plan of a fifth layer of a flexible dc offshore converter station.

Fig. 8 shows a floor plan of a sixth floor of the flexible dc offshore converter station.

Fig. 9 shows a floor plan of a seventh floor of the flexible direct current offshore converter station.

Fig. 10 shows a system topology for a flexible dc offshore converter station.

Description of element numbers: the flexible direct current offshore converter station 1, the first layer 11, the seawater lifting equipment room 111, the second layer 12, the fire pump room 121, the third layer 13, the main control room 131, the fourth layer 14, the cable layer unit 141, the GIS equipment room bottom 142, the fifth layer 15, the GIS equipment room middle 151, the converter transformer unit 152, the sixth layer 16, the GIS equipment room top 161, the seventh layer 17, the crane 171, the upper and lower bridge arm layered structure 18, the upper bridge arm valve hall 181, the polar direct current field 182, the lower bridge arm valve hall 183, the neutral direct current field 184, the converter valve 185, the land-based converter station 2, the total metal loop 3, the collecting end 31, the dispersing end 32, the neutral sea cable 4, the positive pole sea cable 5 and the negative pole sea cable 6.

Detailed Description

Further advantages and effects of the present invention will become apparent to those skilled in the art from the disclosure of the present invention, which is described by the following specific examples.

It should be understood that the structures, proportions, sizes, etc. shown in the drawings are for the purpose of understanding and reading the disclosure, and are not intended to limit the scope of the invention, which is defined by the appended claims, but rather by the claims, unless otherwise indicated, and unless otherwise indicated, all changes in structure, proportions, or otherwise, used by those skilled in the art, are included in the spirit and scope of the invention. Also, the terms such as "upper," "lower," "left," "right," "middle," and "a" and the like recited in the present specification are merely for descriptive purposes and are not intended to limit the scope of the invention, but are intended to provide relative positional changes or modifications without materially altering the technical context in which the invention may be practiced.

As shown in fig. 1, the present invention provides a power transmission system for a common metal loop of a flexible direct current offshore converter station, comprising:

A plurality of flexible direct current offshore converter stations 1, wherein each flexible direct current offshore converter station 1 adopts a symmetrical bipolar wiring structure so as to still have half power transmission capability when a monopole fault occurs on a direct current side, one flexible direct current offshore converter station 1is used as a neutral line collecting station, and neutral line submarine cables 4 of the rest flexible direct current offshore converter stations 1 are collected to the neutral line collecting station;

The system comprises a plurality of land-based converter stations 2, wherein all the land-based converter stations 2 are in one-to-one correspondence with all the flexible direct current marine converter stations 1, and each land-based converter station 2 is connected with the corresponding flexible direct current marine converter station 1 through a positive cable submarine cable 5 and a negative cable 6;

And only one total metal loop 3 is arranged, the length of the total metal loop 3 is matched with the offshore distance of the neutral line collecting station, two end points of the total metal loop 3 along the self extending direction are respectively a collecting end 31 and a dispersing end 32, the collecting end 31 of the total metal loop 3 is connected with the neutral line collecting station, the dispersing end 32 of the total metal loop 3 extends to a coastline near one of the land-based converter stations 2, the dispersing end 32 of the total metal loop 3 is divided into a plurality of neutral branch lines, and all the neutral branch lines are connected with all the land-based converter stations 2 in a one-to-one correspondence.

In the invention, on one hand, each flexible direct current offshore converter station 1 adopts a symmetrical bipolar wiring structure, so that when a single-pole fault occurs on the direct current side, the flexible direct current offshore converter station 1 still has half power transmission capacity, thereby greatly reducing fault loss, and being suitable for large-capacity offshore wind power delivery scenes which are far away from land and are difficult to overhaul. On the other hand, the flexible direct current offshore converter stations 1 share one total metal loop 3, specifically, one of the flexible direct current offshore converter stations 1 is used as a neutral line collecting station, and neutral line sea cables 4 of the rest of the flexible direct current offshore converter stations 1 are collected to the neutral line collecting station; the collecting end 31 of the total metal return line 3 is connected to the neutral sea cable 4 of the neutral collecting station, so that the neutral sea cable can be uniformly sent to the coastline near one of the land-based converter stations 2 through the neutral collecting station, and finally the neutral sea cable is connected with all the land-based converter stations 2 in a one-to-one correspondence through all the neutral branch lines respectively. Therefore, the power transmission system can remarkably improve the power supply reliability of the flexible direct current offshore converter station 1, increase the generating capacity income, simultaneously reduce the length of the neutral cable and remarkably reduce the manufacturing cost of the cable.

Therefore, the power transmission system can greatly reduce the overall cost of the neutral line submarine cable, has half power transmission capacity when a monopole fault occurs on the direct current side, and is particularly suitable for large-capacity open sea wind power transmission scenes which are far away from land and difficult to overhaul.

In a specific implementation, the number of the flexible direct current offshore converter stations 1 and the number of the land-based converter stations 2 may be three, and the flexible direct current offshore converter station 1 located in the middle is used as the neutral line collecting station.

Only the construction structure and the equipment distribution of the flexible dc offshore converter station 1 will be described, and the electrical connection between the electrical components not described in the present application is in the prior art, and will not be described again.

Further, as shown in fig. 2 to 10, in order to facilitate the use of the symmetrical bipolar junction structure of the flexible dc offshore converter station 1 and to make the overall structure of the flexible dc offshore converter station 1 more compact, the overall dimension of the converter body of the flexible dc offshore converter station 1 is 110m x 91m x 45m, the dipoles in the symmetrical bipolar junction structure of the flexible dc offshore converter station 1 are respectively pole one and pole two (may also be referred to as pole 1 and pole 2, or pole i and pole ii), the flexible dc offshore converter station 1 comprises four valve hall units and four dc field units, the valve hall units may be 44m x40 m x 15m or 44m x40 m x 21.5m, the dc field units may be 44m x40 m x 15m, a converter valve bank or a converter valve tower is arranged in each valve hall unit, the converter valve bank or the converter valve tower is provided with a plurality of converter valves 185 which are regularly arranged, the size of the converter valve tower is 44m multiplied by 40m multiplied by 15m, a reactor (such as a smoothing reactor) and an AIS power distribution device (fully called Air Insulated Switchgear of AIS) are arranged in each DC field unit, four valve hall units are respectively an upper bridge arm valve hall 181 of the pole one, an upper bridge arm valve hall 181 of the pole two, a lower bridge arm valve hall 183 of the pole one and a lower bridge arm valve hall 183 of the pole two, and four DC field units are respectively an polar line DC field 182 of the pole one, an polar line DC field 182 of the pole two, a neutral line DC field 184 of the pole one and a neutral line DC field 184 of the pole two; the flexible direct current offshore converter station 1 further comprises an alternating current field, converter transformer units 152 and station transformer units, alternating current GIS power distribution devices (Gas Insulated Switchgear ) are arranged in the alternating current field, the alternating current GIS power distribution devices are connected with an offshore wind turbine, and the number of the converter transformer units 152 is four.

Further, in the symmetrical bipolar flexible direct current system, the direct current bias exists in the converter transformer unit 152, the conventional alternating current GIS power distribution device cannot be disconnected, the converter transformer unit 152 is connected with a converter valve bank or a converter valve tower of the valve hall unit through the direct current GIS power distribution device, and the network side of the converter transformer unit 152 is connected with a 66kV offshore wind turbine through a 66kV alternating current GIS power distribution device.

Further, referring to fig. 2 specifically, for connection and connection between electrical devices, the flexible dc offshore converter station 1 adopts an upper and lower bridge arm layered structure 18, an upper bridge arm valve hall 181 of the first pole, an upper bridge arm valve hall 181 of the second pole, an polar line dc field 182 of the first pole, and an polar line dc field 182 of the second pole are all located at a first height, a lower bridge arm valve hall 183 of the first pole, a lower bridge arm valve hall 183 of the second pole, a neutral line dc field 184 of the first pole, and a neutral line dc field 184 of the second pole are all located at a second height, the second height is greater than the first height, the upper bridge arm of the first pole is located in the upper bridge arm valve hall 181 of the first pole, the upper bridge arm of the second pole is located in the upper bridge arm valve hall 181 of the second pole, the lower bridge arm of the first pole is located in the lower bridge arm valve hall 183 of the first pole, and the lower bridge arm of the second pole is located in the lower bridge arm valve hall 183 of the second pole; the top of the neutral line DC field 184 of the first pole and the top of the neutral line DC field 184 of the second pole are provided with a plurality of overhauling holes. In the current embodiment, the upper bridge arm valve hall 181 may have a size of 44m×40m×21.5m, and the pole line direct current field 182 may have a size of 32m×40m×21.5m.

Further, referring specifically to fig. 2, in order to further facilitate connection between electrical devices and to facilitate arrangement of the symmetrical bipolar junction structure, the flexible dc-sea converter station has a seven-layer structure, each layer having a height of 7.5m, from bottom to top, respectively a first layer 11 (referring specifically to fig. 3), a second layer 12 (referring specifically to fig. 4), a third layer 13 (referring specifically to fig. 5), a fourth layer 14 (referring specifically to fig. 6), a fifth layer 15 (referring specifically to fig. 7), a sixth layer 16 (referring specifically to fig. 8), and a seventh layer 17 (referring specifically to fig. 9); the first layer 11 is provided with a seawater lifting device room 111, a sodium hypochlorite treatment room and a first auxiliary device room; the second layer 12 is provided with a fire pump room 121, a diesel generator room, a 400V station electricity room, a storage battery room and a second auxiliary equipment room; the third layer 13 is provided with a main control room 131, a valve cooling equipment room and a third auxiliary equipment room; the fourth layer 14 is provided with a cable layer unit 141 and a GIS device room bottom 142; the fifth layer 15 is provided with a GIS equipment room middle part 151, a converter transformer unit 152 and a station transformer unit; the sixth layer 16 is provided with a GIS device room top 161 and a motorized room; the seventh layer 17 is provided with a crane 171, a helicopter deck and an equipment room manhole. Wherein, the GIS equipment room bottom 142, the GIS equipment room middle 151 and the GIS equipment room top 161 together form the whole of the GIS equipment room; the converter transformer unit 152 may occupy only the fifth layer 15, or may occupy both the fifth layer 15 and the sixth layer 16.

Further, in order to make the layout of the symmetrical bipolar junction structure more compact, the first upper bridge arm valve hall 181, the second upper bridge arm valve hall 181, the first polar direct current field 182 and the second polar direct current field 182 occupy the first layer 11 to the third layer 13; the alternating-current side of the converter valve bank is connected with an alternating-current side current measuring device, the alternating-current side current measuring device is connected with an alternating-current side incoming line sleeve, the direct-current side of the converter valve bank is connected with a direct-current side current measuring device, and the direct-current side current measuring device is connected with a direct-current side outgoing line sleeve; the converter transformer unit 152 enters the upper bridge arm valve hall 181 from the top of the third layer 13 through an alternating current side wire inlet sleeve after being connected with a direct current GIS power distribution device, and the alternating current side wire outlet sleeve of the upper bridge arm is arranged on the upper side of the upper bridge arm valve hall 181; the direct-current side outlet sleeve of the upper bridge arm is horizontally arranged on the upper side of the valve hall 181 of the upper bridge arm, and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the upper bridge arm valve hall 181 is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester.

Further, in order to convert alternating current of the wind power plant into direct current, the converter valve towers are of a quadruple valve structure, and three converter valve towers form each phase of bridge arm; bridge arm reactors in the direct current field units are connected with a converter valve tower through wall bushings, and the bridge arm reactors are connected to an AIS distribution device after converging through hanging pipe nuts.

Further, the lower bridge arm valve hall 183 of the first pole, the lower bridge arm valve hall 183 of the second pole, the neutral line direct current field 184 of the first pole, and the neutral line direct current field 184 of the second pole occupy the fourth layer 14 to the sixth layer 16; the alternating-current side of the converter valve bank is connected with an alternating-current side current measuring device, the alternating-current side current measuring device is connected with an alternating-current side incoming line sleeve, the direct-current side of the converter valve bank is connected with a direct-current side current measuring device, and the direct-current side current measuring device is connected with a direct-current side outgoing line sleeve; the converter transformer unit 152 enters a lower bridge arm valve hall 183 through an alternating-current side wire inlet sleeve after being connected with a direct-current GIS power distribution device, and the alternating-current side wire outlet sleeve of the lower bridge arm is arranged in the middle of the lower bridge arm valve hall 183; the direct-current side outlet sleeve of the lower bridge arm is horizontally arranged on the upper side of the valve hall 183 of the lower bridge arm, and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the lower bridge arm valve hall 183 is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester. In the current embodiment, the size of the lower bridge arm valve hall 183 may be 44m×40m×21.5m, and the size of the neutral line direct current field 184 may be 32m×40m×21.5m. The neutral dc field is furthermore connected via an AIS distribution device to a neutral cable 4 or to a total metal return 3. In the flexible dc offshore converter station 1 as a neutral line concentration station, the neutral line dc field is connected via an AIS distribution device to the total metal return line 3. In the remaining flexible dc offshore converter station 1, the neutral dc field is connected to the neutral cable 4 via an AIS distribution device. All the neutral cables 4 are connected together at the collection end 31 of the total metallic return 3.

Further, in order to facilitate the cable to pass through, the cable of the lower bridge arm directly enters the middle part of the lower bridge arm valve hall 183 from the GIS equipment room and through the alternating current side outlet sleeve.

As shown in fig. 10, each of the flexible dc offshore converter stations has a pole one and a pole two, each pole having a symmetrical structure. For example, the pole one comprises two first lines connected in parallel, and the first lines are provided with a converter transformer unit 152 and a circuit breaker; the first pole further comprises two parallel second lines, a converter valve 185 and a reactor are arranged on the second lines, one second line is connected to the positive pole cable 5, and the other second line is connected to the neutral line cable 4 or the total metal loop 3 after being connected with the neutral bus switch. In the flexible dc offshore converter station 1 as a neutral line concentration station, one of the second lines is connected to the positive line sea cable 5 and the other second line is connected to the total metal return line 3 after connection of the neutral bus switch. In the remaining flexible dc offshore converter station 1, one of the second lines is connected to the positive line sea cable 5 and the other second line is connected to the neutral line sea cable 4 after connection of the neutral bus bar switch. In addition, the first circuit is connected in series with the second circuit. The second electrode is the same circuit and will not be described again.

In conclusion, the invention can greatly reduce the total cost of the neutral line submarine cable, has half power transmission capability when the direct current side has a monopole fault, and is particularly suitable for being applied to a large-capacity open sea wind power transmission scene which is far away from land and is difficult to overhaul. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.

Claims (5)

1. A power transmission system for a flexible direct current marine converter station common metal return line, comprising:

The system comprises a plurality of flexible direct current offshore converter stations (1), wherein each flexible direct current offshore converter station (1) adopts a symmetrical bipolar wiring structure, one flexible direct current offshore converter station (1) is used as a neutral line collecting station, and neutral line sea cables (4) of the rest flexible direct current offshore converter stations (1) are collected to the neutral line collecting station;

The system comprises a plurality of land-based converter stations (2), wherein all the land-based converter stations (2) are in one-to-one correspondence with all the flexible direct current marine converter stations (1), and each land-based converter station (2) is connected with the corresponding flexible direct current marine converter station (1) through a positive pole cable (5) and a negative pole cable (6) respectively;

The length of the total metal loop (3) is matched with the offshore distance of the neutral line collecting station, two end points of the total metal loop (3) along the extending direction of the total metal loop are collecting ends (31) and dispersing ends (32) respectively, the collecting ends (31) of the total metal loop (3) are connected to the neutral line collecting station, the dispersing ends (32) of the total metal loop (3) extend to the coastline near one of the land-based converter stations (2), the dispersing ends (32) of the total metal loop (3) are divided into a plurality of neutral branch lines, and all the neutral branch lines are connected with all the land-based converter stations (2) in a one-to-one correspondence manner;

The double poles in the symmetrical double pole wiring structure of the flexible direct current offshore converter station (1) are respectively a pole one and a pole two, the flexible direct current offshore converter station (1) comprises four valve hall units and four direct current field units, a converter valve bank or a converter valve tower is arranged in each valve hall unit, a smoothing reactor and an AIS distribution device are arranged in each direct current field unit, the four valve hall units are respectively an upper bridge arm valve hall (181) of the pole one, an upper bridge arm valve hall (181) of the pole two, a lower bridge arm valve hall (183) of the pole one and a lower bridge arm valve hall (183) of the pole two, and the four direct current field units are respectively an polar line direct current field (182) of the pole one, an polar line direct current field (182) of the pole two, a neutral line direct current field (184) of the pole one and a neutral line direct current field (184) of the pole two; the flexible direct current offshore converter station (1) further comprises an alternating current field, converter transformer units (152) and station transformer units, an alternating current GIS power distribution device is arranged in the alternating current field and connected with an offshore wind turbine, and the number of the converter transformer units (152) is four;

The converter transformer unit (152) is connected with a converter valve bank or a converter valve tower of the valve hall unit through a direct-current GIS power distribution device, and the network side of the converter transformer unit (152) is connected with a 66kV offshore wind turbine through a 66kV alternating-current GIS power distribution device;

the flexible direct current offshore converter station (1) adopts an upper bridge arm layered structure (18), an upper bridge arm valve hall (181) of a first pole, an upper bridge arm valve hall (181) of a second pole, an polar line direct current field (182) of the first pole and an polar line direct current field (182) of the second pole are all located at a first height, a lower bridge arm valve hall (183) of the first pole, a lower bridge arm valve hall (183) of the second pole, a neutral line direct current field (184) of the first pole and a neutral line direct current field (184) of the second pole are all located at a second height, the second height is larger than the first height, the upper bridge arm of the first pole is arranged in the upper bridge arm valve hall (181) of the first pole, the upper bridge arm of the second pole is arranged in the upper bridge arm valve hall (181) of the second pole, the lower bridge arm of the first pole is arranged in the lower bridge arm valve hall (183) of the first pole, and the lower bridge arm of the second pole is arranged in the lower bridge arm valve hall (183) of the second pole; a plurality of overhaul holes are formed in the top of the neutral line direct current field (184) of the first pole and the top of the neutral line direct current field (184) of the second pole;

The flexible direct current offshore converter station (1) has a seven-layer structure, and comprises a first layer (11), a second layer (12), a third layer (13), a fourth layer (14), a fifth layer (15), a sixth layer (16) and a seventh layer (17) from bottom to top; the first layer (11) is provided with a seawater lifting equipment room (111), a sodium hypochlorite treatment room and a first auxiliary equipment room; the second layer (12) is provided with a fire pump room (121), a diesel generator room, a 400V station electricity room, a storage battery room and a second auxiliary equipment room; the third layer (13) is provided with a main control room (131), a valve cooling equipment room and a third auxiliary equipment room; the fourth layer (14) is provided with a cable layer unit (141) and a GIS equipment room bottom (142); the fifth layer (15) is provided with a GIS equipment room middle part (151), a converter transformer unit (152) and a station transformer unit; the sixth layer (16) is provided with a GIS equipment room top (161) and a maneuvering room; the seventh layer (17) is provided with a crane (171), a helicopter platform and an equipment room manhole.

2. The power transmission system of a flexible direct current marine converter station common metal return line of claim 1, wherein: the first upper bridge arm valve hall (181), the second upper bridge arm valve hall (181), the first polar direct current field (182) and the second polar direct current field (182) occupy the first layer (11) to the third layer (13); the alternating current side of the converter valve bank is connected with an alternating current side current measuring device, the alternating current side current measuring device is connected with an alternating current side wire inlet sleeve, the direct current side of the converter valve bank is connected with a direct current side current measuring device, and the direct current side current measuring device is connected with a direct current side wire outlet sleeve; the converter transformer unit (152) enters an upper bridge arm valve hall (181) from the top of the third layer (13) through an alternating current side wire inlet sleeve after being connected with a direct current GIS power distribution device, and the alternating current side wire outlet sleeve of the upper bridge arm is arranged on the upper side of the upper bridge arm valve hall (181); the direct-current side outlet sleeve of the upper bridge arm is horizontally arranged on the upper side of the upper bridge arm valve hall (181), and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the upper bridge arm valve hall (181) is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester.

3. A power transmission system for a common metal return line for a flexible direct current marine converter station according to claim 2, wherein: the converter valve towers are of a quadruple valve structure, and three converter valve towers form each phase of bridge arm; bridge arm reactors in the direct current field units are connected with a converter valve tower through wall bushings, and the bridge arm reactors are connected to an AIS distribution device after converging through hanging pipe nuts.

4. The power transmission system of a flexible direct current marine converter station common metal return line of claim 1, wherein: the lower bridge arm valve hall (183) of the first pole, the lower bridge arm valve hall (183) of the second pole, the neutral line direct current field (184) of the first pole and the neutral line direct current field (184) of the second pole occupy the fourth layer (14) to the sixth layer (16); the alternating current side of the converter valve bank is connected with an alternating current side current measuring device, the alternating current side current measuring device is connected with an alternating current side wire inlet sleeve, the direct current side of the converter valve bank is connected with a direct current side current measuring device, and the direct current side current measuring device is connected with a direct current side wire outlet sleeve; the converter transformer unit (152) enters a lower bridge arm valve hall (183) through an alternating-current side inlet wire sleeve after being connected with a direct-current GIS power distribution device, and the alternating-current side outlet wire sleeve of the lower bridge arm is arranged in the middle of the lower bridge arm valve hall (183); the direct-current side outlet sleeve of the lower bridge arm is horizontally arranged on the upper side of a valve hall (183) of the lower bridge arm, and a direct-current side lightning arrester is arranged right below the direct-current side outlet sleeve; the ground of the lower bridge arm valve hall (183) is provided with a converter valve tower, a direct current side current measuring device, a direct current side post insulator, a direct current side grounding switch and a direct current side lightning arrester.

5. The power transmission system for a common metal return line of a flexible direct current marine converter station of claim 4, wherein: and the cable of the lower bridge arm directly enters the middle part of a valve hall (183) of the lower bridge arm from the GIS equipment room and through an alternating current side outlet sleeve.