CN218976354U - High-power-density true bipolar flexible direct-current offshore converter station - Google Patents

Abstract

The utility model provides a high-power-density true bipolar flexible direct current offshore converter station, which forms a compact arrangement scheme by applying a high-capacity converter transformer technology, an alternating current/direct current GIS equipment technology, a layering arrangement technology of a direct current polar distribution device and a neutral wire distribution device and an air insulation equipment integration arrangement technology under the condition of simplified system wiring and comprehensively utilizing methods such as air clearance dimension, antimagnetic clearance space and the like. According to the utility model, only the direct current polar line current conversion area and the direct current neutral line current conversion area of the whole current conversion station are air insulation equipment, and the rest areas are equipment with the medium insulation shell grounded, so that the space utilization rate is greatly improved, the unit power weight of the current conversion station can be reduced to about 0.75-1.0 kiloton/gigawatt from the traditional 1.5-2.0 kiloton/gigawatt, and the unit power weight is optimized to be nearly 50% compared with the traditional scheme.

Description

High-power-density true bipolar flexible direct-current offshore converter station

Technical Field

The utility model belongs to the design technology of offshore wind power flexible direct current transmission converter stations, and particularly relates to a high-power-density true bipolar flexible direct current offshore converter station.

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.

The existing offshore wind power flexible direct current transmission technical scheme (such as a marine converter station for a flexible direct current transmission system in patent document CN 110042819A) generally adopts a symmetrical monopole transmission topology, the topology has few used equipment and low manufacturing cost level, the offshore converter station is relatively convenient to transport and install, but the technology is generally suitable for transmission capacity of 1000 MW-1600 MW, and the reliability is relatively slightly low. With further deep open sea of offshore wind power projects, a power transmission scheme with larger capacity, economy and rationality and less occupied sea area is required, and a true bipolar flexible direct current power transmission system is more applicable. The true bipolar flexible direct current transmission system is suitable for the transmission of 2000MW and above, but the configuration of the true bipolar system is complex, the occupied space is large, and therefore the upper block size of the offshore converter station is huge.

On the other hand, the existing offshore wind power flexible direct current converter station has more air insulation equipment, and high voltage needs to be insulated through enough air clear distance and antimagnetic clear distance to ensure safety, so that more hollow areas exist in the converter station, and the equipment arrangement compactness degree is insufficient and the overall utilization rate is not high. Under the prior art, the unit power weight of the converter station block is 1.5-2 ten thousand tons/gigawatt.

By combining the two factors, for the open sea large-scale power transmission engineering, the real bipolar offshore converter station has the problems of huge upper block size, low power density, and thus a series of problems of difficult construction and installation, long construction time, difficult control of structural deformation indexes and the like are caused; even an excessively large upper block may present a significant challenge for transportation installation, possibly due to limited shipping volumes, affecting the feasibility of engineering practices. Therefore, the conventional single-bipolar offshore converter station technology represented by patent document CN 110042819A cannot be fully carried out as a true bipolar offshore converter station.

In summary, research on a high-power-density true bipolar offshore converter station is needed, and the high-power-density true bipolar offshore converter station has the functions of the converter station, so that the feasibility of engineering can be guaranteed, the construction difficulty can be reduced, and the construction period can be shortened.

Disclosure of Invention

The utility model aims to provide a high-power-density true bipolar flexible Direct Current (DC) offshore converter station, which aims at the problems of complex system, large occupied space and limited ship transportation capacity of the offshore converter station with the capacity of 2000MW and above.

For this purpose, the above object of the present utility model is achieved by the following technical solutions:

based on the existing standard system and the general requirements of industry, the limit requirements which are required to be met by the offshore converter station structure are combed from three aspects of marine hydrology, construction and installation conditions and operation and maintenance comfortableness, the input boundary conditions of the converter station design are formed, and the size and the weight of the platform are controlled.

On the premise of ensuring safety and reliability, the electric wiring is simplified, the occupied area of the offshore converter station is reduced by reducing equipment configuration, and the main simplification content comprises:

(1) The method comprises the steps of applying high-capacity converter transformers, wherein the converter transformers are divided into two groups, and the two groups of transformers are arranged at the position: 1) The two groups of transformers can be mutually backed up, and when one group of transformers fails, the other group of transformers can bear part of electric energy transmission; 2) Each group of transformers is matched with one pole of direct current transmission, the two poles are independent, and the safety and reliability of the transmission are guaranteed. After the converter transformers are arranged in two groups, bus connection wires of a transformer net side and a valve side can be omitted, so that the connection wires are greatly simplified, and the equipment configuration is reduced;

(2) The breaker at the valve side of the converter transformer is canceled, and only sectional equipment such as an isolating switch, a grounding switch and the like are reserved, so that the running safety of a direct current system is ensured through the improvement of a control strategy, and the converter transformer valve side application of an alternating current-direct current hybrid GIS is feasible;

(3) And the switch configurations such as a high-speed switch (NBS) of a neutral line loop bus at a transmitting end, a high-speed grounding switch (NBGS) of the neutral bus, a metal loop transfer switch (MRTB) and the like in the traditional flexible direct current transmission system are canceled, and the switch configurations are simplified into direct current isolating switches, so that the polar line equipment and the neutral line equipment have feasibility by adopting a direct current GIS.

The configuration of the air insulation equipment is reduced by using medium insulation equipment such as a direct current GIS, an alternating current-direct current GIS and the like, so that the occupied space of the switch equipment is greatly reduced, and the method specifically comprises the following steps:

(1) And the converter transformer valve side adopts AC/DC mixed GIS equipment, and each of the poles 1 and 2 is provided with one set. The equipment integrates an AC/DC lightning arrester, an AC/DC hybrid isolating switch and the like into GIS equipment, compared with the conventional open AIS equipment, the equipment does not need to reserve air clearance spaces between equipment and between equipment and a steel structure, and the occupied area can be saved by at least 50%;

(2) The direct current polar line equipment adopts high-voltage direct current GIS equipment, and the anode and the cathode are respectively one set. The equipment integrates a direct current lightning arrester, a direct current transformer, a direct current voltage divider, a direct current isolating switch and the like into GIS equipment, compared with open AIS equipment, the equipment does not need to reserve air clearance spaces between equipment and between equipment and a steel structure, and the occupied area can be saved by at least 30%;

(3) And the direct-current neutral line equipment uses a medium-voltage direct-current GIS, and the total stations share one set. The device integrates a pole 1 neutral line loop, a pole 2 neutral line loop, a direct current isolating switch of a neutral line outlet loop, a direct current lightning arrester, a direct current transformer, a direct current voltage divider and other devices and is integrated into a GIS. In order to ensure the safety and reliability of the equipment, the pole 1, pole 2 neutral line equipment and neutral line outlet loop equipment are separated by adopting different air chambers, compared with the open-type direct current AIS equipment, the air clearance spaces between equipment and between equipment and steel structures are not required to be reserved, and the occupied area can be saved by more than 50 percent.

The general arrangement scheme of the upper assembly blocks of the offshore converter station still adopts a three-factory building type of 'one main and two auxiliary' in the traditional technology, and simultaneously performs compact transformation, and the specific technical scheme is as follows.

(1) The main factory building is positioned in the center of the station and comprises a current converting area and a direct current area,

the converter valve and the direct current bridge arm loop are arranged in layers according to polar lines and neutral line equipment in the height direction, the polar line equipment is arranged on 1-3 large through layers, the neutral line equipment is arranged on 4-6 large through layers, and four converter regions and three direct current regions are respectively formed;

the room configuration of a main factory building of the convertor station is simplified, the valve tower of the convertor region and the bridge arm reactor of the direct current region are arranged in the same room, the separation arrangement between the traditional valve hall and the reactor chamber is canceled, the partition wall plate is canceled, the wall bushing arrangement is canceled, and the occupied area of a plane is effectively reduced by more than 20%. Specifically, in conventional arrangement, the converter valve and the bridge arm reactor are respectively and independently arranged in different distribution device chambers, so that the converter valve and the bridge arm reactor need to be checked for the electrified clear distance respectively, and the clear distance between the converter valve and the bridge arm reactor at least needs to be as follows: l=clean air gap of converter valve to ground + steel structure (wall thickness) +clean air gap of bridge arm reactor to ground or anti-magnetic gap. However, after the method of the utility model is adopted, the distance between the converter valve and the bridge arm reactor is as follows: l=max (air clearance between the converter valve and the bridge arm, anti-magnetic clearance of the bridge arm reactor), which is the maximum value between the two clearance, effectively comprehensively utilizes the space, and can effectively reduce the space occupied by the air clearance.

(2) Two auxiliary plants are respectively located at two sides of the main plant, and an alternating current auxiliary plant and a direct current auxiliary plant are formed by corresponding to an incoming wiring and an outgoing wiring, wherein: the alternating-current side auxiliary factory building is sequentially provided with a cable channel and valve cooling system, a 66kV inlet GIS, a main control room, secondary equipment and storage batteries, an alternating-current and direct-current GIS, a converter transformer and other host equipment from bottom to top; the direct-current side auxiliary factory building is sequentially provided with main electrical equipment such as a high-voltage direct-current GIS, a medium-voltage direct-current GIS and the like from bottom to top.

(3) The temporary working and living modules of personnel are additionally arranged on the outer side of the direct-current side auxiliary workshop, and the temporary working and living modules comprise a rest room, a tool room, a spare part warehouse and the like and are used for temporarily guarding the personnel for system debugging, operation and maintenance after the upper part of the converter station is assembled on the sea. The weight of the living module is about 1/12-1/8 of the total weight of the converter station module, the living module can play a role in balancing the adverse problem of eccentricity caused by heavy alternating current measuring equipment during offshore transportation and installation, and the extra risk brought to a construction ship machine is reduced; after the converter station is put into operation, the module can be removed and recycled or used as a part of a permanent life platform beside the converter station to provide a connecting channel for the converter station and the life platform.

The utility model provides a high-power-density true bipolar flexible direct current offshore converter station, which forms a compact arrangement scheme by applying a high-capacity converter transformer technology, an alternating current/direct current GIS equipment technology, a layering arrangement technology of a direct current polar distribution device and a neutral wire distribution device and an air insulation equipment integration arrangement technology under the condition of simplified system wiring and comprehensively utilizing methods such as air clearance dimension, antimagnetic clearance space and the like, and has the following advantages that:

1) The offshore converter station has small occupied area and compact and reasonable structure, and provides guarantee for long-term maintenance of stability and reliability of the converter station adapting to offshore environment; through optimization of a system level, the number and complexity of equipment are reduced, and space and the size of an upper block of a converter station are effectively saved;

2) The medium insulation equipment GIS is selected and used, and equipment is reasonably combined, so that on one hand, the space of air insulation clearance is reduced, the space requirement for equipment arrangement is reduced, on the other hand, the installation and operation are convenient, the interfaces between the electrical equipment and a converter station platform are reduced, and the equipment types and maintenance workload are reduced;

3) Through the optimization of the whole arrangement level, the occupied area of the offshore converter station is comprehensively reduced, the functional partition of each distribution area is definite, the open type equipment is gathered in the converter area as much as possible, and GIS equipment is adopted in the other areas as much as possible, so that on one hand, the connection equipment of each area is reduced, and on the other hand, the space is comprehensively utilized with high efficiency, wherein compared with the arrangement scheme adopting the prior art, the plane projection area of a main factory building can be saved by more than 50%, the power density of the converter station is reduced from the traditional 1.5-2.0 kilotons/gigawatt to about 0.75-1.0 kilotons/gigawatt, and is optimized by nearly 50% compared with the traditional scheme;

4) The utility model can effectively solve the problems of huge volume and overlarge weight of the offshore converter station platform, reduces the purchase and manufacturing costs of the steel structure, and has higher engineering economy;

5) The utility model has compact space arrangement, small occupied area and light weight, and simultaneously, the span of the main factory building (namely the slotting width corresponding to the lower foundation) is suitable for the wide sex of common construction ships with corresponding tonnages, thereby being beneficial to the model selection of offshore construction ships, reducing the offshore construction difficulty, shortening the construction period and further reducing the project construction cost.

Drawings

Fig. 1 is a topology diagram of the wiring of a high power density marine true bipolar flexible dc converter station provided by the present utility model.

Fig. 2 is a schematic diagram of a layer 2 of a high power density offshore true bipolar flexible dc converter station platform provided by the present utility model.

Fig. 3 is a schematic diagram of a layer 1 of a high power density offshore true bipolar flexible dc converter station platform provided by the utility model.

Fig. 4 is a schematic diagram of a layer 3 of a high power density offshore true bipolar flexible dc converter station platform provided by the utility model.

Fig. 5 is a schematic diagram of 5-6 layers of a high power density offshore true bipolar flexible direct current converter station platform provided by the utility model.

Fig. 6 is a schematic diagram of a layer 4 of a high power density offshore true bipolar flexible dc converter station platform provided by the utility model.

Fig. 7 is a typical cross-sectional view of a high power density marine true bipolar flexible dc converter station provided by the present utility model.

Detailed Description

For a more particular description of the utility model, the utility model is further described below with reference to the drawings.

The marine converter station wiring diagram is shown in fig. 1, and the true bipolar system is divided into an alternating current area, a converter area, a connecting area, a converter area, a direct current area and the like. The alternating-current regional equipment is mainly 66kV GIS and mainly plays a role in collecting wind energy of a wind power plant. The collected alternating current electric energy is led to a high-capacity converter transformer, and the transformer matches alternating current voltage with modulation voltage at the network side of a converter valve. Taking the pole 1 as an example (the same as the pole 2), the electric energy passing through the converter transformer is led to an alternating current-direct current hybrid GIS, and the electric energy passing through the GIS is led to a pole 1 polar line bridge arm loop and a pole 1 neutral line bridge arm loop respectively. The pole 1 polar line bridge arm is divided into A, B, C three loops, and the pole 1 neutral line bridge arm is divided into A, B, C three loops, and six bridge arm loops are provided. After the bridge arm loops are converged through the bridge arm reactors, an polar line direct current bus and a neutral line direct current bus are respectively formed, and in a direct current region, polar line direct current sea cables and neutral line direct current sea cables are respectively led to be connected through polar line direct current GIS and neutral line direct current GIS loops, and are sent to a land convertor station through the sea cables.

As shown in fig. 2, the offshore converter station 2 is arranged in layers, which is one of the core arrangement areas of the converter station. The field is mainly divided into five areas, which are respectively: 1) Ac distribution device areas 101, 102, the main arrangement equipment is 66kV GIS 11; 2) Auxiliary equipment areas 201 and 202 mainly comprise areas such as platform power supply system equipment (low-voltage alternating current and direct current), platform heating and ventilation system equipment, spare parts and the like; 3) The pole line commutation areas 301 and 302 are mainly provided with bridge arm equipment, including pole line commutation valves 31 and 32, pole line bridge arm reactors 35 and 36, direct current grounding switches 33 and 34, bridge arm direct current side converging equipment 37 and 38 and other equipment; 4) Polar dc distribution device areas 401, 402, mainly arranged polar dc GIS devices 41, 42; 5) The living module areas L01-L03 are mainly arranged as follows: the elevator cabs L01 are arranged on the south and north sides, the debugging and operation rest room L02 is arranged in the middle, and the outer walkway L03 is arranged on the east outer side. The module is divided into 3 layers, and occupies about 1/12 of the total weight, and is mainly used for adjusting the eccentricity of the converter station in offshore transportation and installation, ensuring the stress rationality of offshore installation and reducing the offshore construction difficulty; meanwhile, the module can be used for operation and maintenance during offshore debugging, temporary equipment storage and spare part storage, greatly reduces the debugging difficulty of two parts of equipment at sea/land, saves the space of the whole convertor station, and can be lifted and removed integrally according to the on-site requirement after normal operation, so that the whole weight of the convertor station is reduced.

As shown in fig. 3, the layer 1 arrangement of the offshore converter station is different from the layer 2 arrangement in that a cable layer and a valve cooling system are arranged below an alternating current power distribution device area, an auxiliary system platform power supply system (low-voltage alternating current/direct current), a fresh air machine room and the like; the auxiliary module is different in that a restaurant L12, an office meeting room L13 and a spare part room L14 are arranged on one layer, and a connecting step bridge L15 can be arranged on the other layer to realize interconnection with other functional platforms.

As shown in fig. 4, the layer 3 arrangement of the offshore converter station is different from the layer 2 arrangement in that the upper layer of the ac distribution device area is arranged as a secondary equipment area, an operation control area and the like; the auxiliary module is arranged between temporary equipment in the layer and used for placing land/marine electrical debugging equipment, temporary oil tanks and related equipment materials.

As shown in fig. 5, which shows the offshore converter stations 5-6, mainly the arrangement of the equipment of the 5 th and 6 th layers is shown, which area is also one of the core arrangement areas of the converter stations. The field region is mainly divided into four types of regions, mainly: 1) Converter transformer areas 501, 502 in which the converter transformers 51, 52 are mainly arranged, serve to match the grid voltage with the converter valve modulation voltage; 2) The neutral line commutation areas 601 and 602 are mainly provided with bridge arm devices, wherein the bridge arm devices comprise neutral line commutation valves 61 and 62, neutral line bridge arm reactors 65 and 66, direct current grounding switches 63 and 64, neutral line bridge arm direct current side confluence devices 67 and 68 and the like; 3) The neutral line dc distribution device region 701 is mainly configured with a neutral line dc GIS device 71, which integrates a pole 1 neutral line dc region device, a pole 2 neutral line dc region device, and a neutral line dc outlet device. 4) Auxiliary equipment areas 801 and 802 are mainly arranged in areas such as a platform power supply system device (low-voltage alternating current and direct current), a platform heating and ventilation system device and the like.

As shown in fig. 6, the layer 4 of the offshore converter station is different from the layer 5-6 of the offshore converter station only in that the transformer areas are adjusted to be ac/dc hybrid GIS areas 901 and 902 in the figure, and a pole 1 ac/dc hybrid GIS device 91 and a pole 2 ac/dc hybrid device 92 are arranged.

As shown in fig. 7, which shows a cross section of an offshore converter station, it can be seen from the figure that ac sea cables are converged from 66kv GIS 11, and the converged loops are led to the low voltage sides of converter transformers 51, 52, and then led from the transformer valve sides to ac/dc GIS 91, 92, and led to dc polar valve halls 301, 302 and dc neutral valve halls 601, 602 through GIL pipes. After the direct current polar valve hall is rectified by the converter valve, each bridge arm loop is led to a bridge arm reactor, and then led to polar direct current GIS 401 and 402 by the bridge arm reactor. After the direct-current neutral line is rectified by the converter valve, each bridge arm loop is led to a bridge arm reactor, after the bridge arm reactors converge, the bridge arm reactors are led to a medium-voltage GIS direct current 71, after the direct-current neutral line passes through the medium-voltage direct-current GIS, a neutral line direct-current submarine cable is led to one layer through a direct-current submarine cable channel and is led to the ocean, and therefore the neutral line direct-current submarine cable is led to a land converter station. The auxiliary modules are arranged in three layers, have the functions of life, spare parts storage, debugging, operation and maintenance equipment arrangement and the like, are independent, and can be removed and reused according to requirements after the converter station is in place.

As shown in fig. 1 to 7, among all the above power distribution devices, only the pole 1 pole line current converting region 301, the pole 2 pole line current converting region 302, the pole 1 neutral line current converting region 601 and the pole 1 neutral line current converting region 602 adopt open devices, and the rest needs to reserve air clearance and antimagnetic clearance equidistance requirements, otherwise air breakdown under overvoltage condition or electromagnetic heating under high power may be caused. The other earthing devices such as GIS equipment and switch cabinet equipment are all adopted, and the earthing device is medium insulation equipment, so that the shell can be earthed, and the operation and installation requirements can be met only by reserving overhaul and maintenance spaces, so that a large amount of space can be saved. For a true bipolar flexible direct current transmission system with the voltage of +/-500 kV, the scheme aims to inhibit the overvoltage level to 1050kV (SIWV) in the areas 301 and 302, the air clear distance is controlled to be within 4 meters, the overvoltage level is inhibited to 650kV (SIWV) in the areas 701 and 702, the air clear distance is controlled to be within 2 meters through the system optimization design and overvoltage inhibition measures, and an advantageous input is created for the compactness of the whole arrangement.

As shown in figures 1-7, the polar line direct current equipment and the neutral line direct current equipment are arranged in a layered mode, the polar line bridge arm reactors, the polar line direct current GIS and other equipment with higher voltage level and heavier weight are arranged at the lower layer, the neutral line bridge arm reactors and the neutral line direct current GIS equipment with slightly lower voltage level and slightly lighter weight are arranged at the upper layer, so that the arrangement can reduce the plane area, fully utilize the height space, and further ensure the reasonable design of the integral structure and the stability of long-term operation of the converter station.

As shown in fig. 1-7, the converter valve and the bridge arm reactor are arranged in the same chamber, so that the space of connecting equipment between the converter valve and the bridge arm reactor is mainly saved, the air clearance and the antimagnetic clearance are subjected to interactive digestion, and the occupation size of the air clearance is reduced.

The above detailed description is intended to illustrate the present utility model by way of example only and not to limit the utility model to the particular embodiments disclosed, but to limit the utility model to the precise embodiments disclosed, and any modifications, equivalents, improvements, etc. that fall within the spirit and scope of the utility model as defined by the appended claims.

Claims (7)

1. A high power density true bipolar flexible dc offshore converter station characterized by: the high-power-density true bipolar flexible direct current offshore converter station comprises an alternating current region, a converter region, a connecting region, a converter region and a direct current region which are sequentially arranged;

a 66kV alternating-current GIS is arranged in the alternating-current area, and the 66kV alternating-current GIS is used for collecting wind energy of a wind power plant;

a plurality of converter transformers are arranged in the converter transformer area and are connected with a 66kV alternating-current GIS in the alternating-current area so as to match alternating-current voltage with modulation voltage at the network side of the converter valve;

an AC/DC hybrid GIS is arranged in the connection area,

a polar line bridge arm loop, a neutral line bridge arm loop and bridge arm reactors respectively connected with the polar line bridge arm loop and the neutral line bridge arm loop in series are arranged in the commutation area;

and the two ends of the neutral line direct current GIS are respectively connected with the bridge arm reactor of the neutral line bridge arm loop and the neutral line direct current submarine cable.

2. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the upper block of the high-power-density true bipolar flexible direct current offshore converter station adopts a main and auxiliary three-factory building type,

the main factory building is positioned in the center of the station and comprises a converter area and a direct current area, converter valves and direct current bridge arm loops are arranged in layers according to polar lines and neutral line equipment in the height direction, the polar line equipment is arranged on 1-3 large through layers, the neutral line equipment is arranged on 4-6 large through layers, and four converter areas and three direct current areas are respectively formed; the valve tower of the current conversion area and the bridge arm reactor of the direct current area are arranged in the same room, the separation arrangement between the traditional valve hall and the reactor chamber is canceled, the partition wall plate is canceled, the wall bushing arrangement is canceled, the occupied area of a plane is effectively reduced by more than 20%, and the distance between the current conversion valve and the bridge arm reactor is as follows: l=max, which is the maximum value between the two clear distances, effectively comprehensively utilizing space;

two auxiliary plants are respectively located at two sides of the main plant, and an alternating current auxiliary plant and a direct current auxiliary plant are formed by corresponding to an incoming wiring and an outgoing wiring, wherein: the alternating-current side auxiliary workshop is sequentially provided with a cable channel and valve cooling system, a 66kV inlet GIS, a main control room, secondary equipment and storage batteries, an alternating-current and direct-current GIS and a converter transformer from bottom to top; the direct-current side auxiliary workshop is sequentially provided with a high-voltage direct-current GIS and a medium-voltage direct-current GIS from bottom to top;

the outside of the direct current side auxiliary factory building is provided with a personnel temporary working and living module which comprises a rest room, a tool room and a spare part warehouse, and is used for temporarily guarding personnel for system debugging, operation and maintenance after the upper part of the converter station is assembled on the sea.

3. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the converter transformer adopts a high-capacity converter transformer, and the converter transformers are divided into two groups: when one group of transformers fails, the other group of transformers can bear partial electric energy transmission, and each group of transformers is matched with one pole of direct current transmission, so that two stages are ensured to be independent relatively, and the safe and reliable transmission is ensured.

4. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the high-power-density true bipolar flexible direct current offshore converter station cancels a converter transformer valve side breaker, and only keeps a disconnecting switch and a grounding switch.

5. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the high-power-density true bipolar flexible direct-current offshore converter station cancels a high-speed switch (NBS) of a neutral line loop bus, a high-speed grounding switch (NBGS) of a neutral bus and a metal loop transfer switch (MRTB) of a traditional flexible direct-current transmission system and is simplified to be a direct-current isolating switch.

6. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the polar line direct current GIS adopts a high-voltage direct current GIS, the anode and the cathode are respectively one set, and the high-voltage direct current GIS integrates a direct current lightning arrester, a direct current transformer, a direct current voltage divider and a direct current isolating switch into the GIS.

7. A high power density true bipolar flexible dc marine converter station according to claim 1, characterized in that: the neutral line direct current GIS adopts a medium voltage direct current GIS, and the total stations are one set, and the medium voltage direct current GIS integrates a neutral line loop, a direct current isolating switch of a neutral line outgoing loop, a direct current lightning arrester, a direct current transformer and a direct current voltage divider into the GIS.

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