Three-phase split-type transformer for + / -500kV offshore wind power flexible direct current transmission

Abstract

The invention relates to a three-phase split-type transformer for + / -500kV offshore wind power flexible direct current transmission. A first network side coil, a valve side coil, a second network side coil and a balance coil are arranged on each phase core column of an iron core from inside to outside; wherein the head end of the first network side coil of each phase and the end of the second network side coil of each phase are respectively introduced into a corresponding network side outlet box on the oil tank and are connected with two parallel network side alternating current cables, and the tail end of the first network side coil of each phase and the tail end of the second network side coil of each phase are respectively converged and connected and then are led out by a corresponding network side neutral point sleeve on the oil tank. The head end of each phase valve side coil is led into a corresponding valve side outlet box on the oil tank and connected with a valve side direct current cable, the tail ends of the phase valve side coils are converged and connected and then led out through a valve side neutral point sleeve on the oil tank, the phase balance coils are sequentially connected, and the two ends of each phase balance coil are led out through corresponding balance sleeves on the oil tank. The purpose that the electric power generated by the offshore wind turbine is directly connected to the offshore platform through the 66-kilovolt three-phase cable is achieved.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, specifically a three-phase split transformer for ±500kV offshore wind power flexible DC transmission. Background Technology

[0002] Currently, flexible DC transmission technology is becoming the main way to transmit wind resources from deep-sea areas. It can promote a high proportion of offshore wind power integration, and the high-voltage, large-capacity, lightweight three-phase flexible DC transformer is more suitable for large-capacity offshore converter platforms. However, the highest valve-side voltage level of the transformer in the existing offshore wind power flexible DC transmission line technology is ±400kV, which cannot meet the increasing requirements of transmission lines. At the same time, the grid-side voltage of the transformer is generally 220kV, which usually needs to be boosted by an offshore substation and collected to the flexible DC transformer. Therefore, each wind farm needs to build a substation and connect it through a three-phase cable. Summary of the Invention

[0003] The purpose of this invention is to provide a three-phase split transformer for ±500kV offshore wind power flexible DC transmission. It adopts a dual-path input (dual split) on the grid side of each phase. Each input uses a dual-cable parallel connection to reduce the voltage on the grid side of the transformer from 220kV to 66kV, thereby realizing the purpose of directly connecting the power generated by the offshore wind turbine to the offshore platform through a 66kV three-phase cable.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A three-phase split transformer for ±500kV offshore wind power flexible DC transmission includes an oil tank and an iron core disposed within the oil tank. Each phase core column of the iron core is fitted with a coil assembly, and the coil assembly includes a first grid-side coil, a valve-side coil, a second grid-side coil, and a balancing coil arranged sequentially from the inside out. The oil tank is equipped with a grid-side outlet box, a first grid-side neutral point bushing, a second grid-side neutral point bushing, a valve-side outlet box, a valve-side neutral point bushing, and a balancing bushing. The first grid-side coil of each phase and the second grid-side coil of each phase... The first end is introduced into the corresponding grid-side outlet box and connected to the corresponding two parallel grid-side AC cables. After the ends of the first grid-side coils of each phase are connected together, they are led out from the first grid-side neutral point bushing. The ends of the second grid-side coils of each phase are connected together and led out from the second grid-side neutral point bushing. The first end of the valve-side coil of each phase is introduced into the corresponding valve-side outlet box and connected to the corresponding valve-side DC cable. After the ends of the valve-side coils of each phase are connected together, they are led out from the valve-side neutral point bushing. The balance coils of each phase are connected end to end in sequence, and both ends are led out from the corresponding balance bushings.

[0006] The grid-side outlet box is equipped with a grid-side bushing, and the beginning ends of the first grid-side coil of each phase and the beginning ends of the second grid-side coil of each phase are respectively connected to two parallel grid-side AC cables introduced into the grid-side outlet box through the grid-side bushing in the corresponding grid-side outlet box.

[0007] The first and second neutral point bushings are respectively located at both ends of the oil tank, and each wire side outlet box is located between the first and second neutral point bushings.

[0008] The valve-side outlet box is equipped with a valve-side bushing, and the first end of each phase valve-side coil is connected to the valve-side DC cable introduced into the valve-side outlet box through the valve-side bushing in the corresponding valve-side outlet box.

[0009] The balancing coil is provided with a balancing coil electrostatic plate and a balancing coil corner ring, wherein the balancing coil electrostatic plate is located at the end of the balancing coil and the balancing coil corner ring is located on the upper side of the balancing coil electrostatic plate.

[0010] The balancing coils of each phase are connected end to end in sequence, and the beginning of the A-phase balancing coil and the end of the C-phase balancing coil are respectively led out from the corresponding balancing bushings on the oil tank.

[0011] The tank wall of the oil tank is provided with an arc-shaped section, and the arc-shaped section is provided with magnetic shielding.

[0012] The tank wall includes staggered arc wall sections and straight wall sections, with the arc wall sections located outside the corresponding coil assembly. The magnetic shielding includes a first magnetic shielding assembly and a second magnetic shielding assembly. Multiple sets of first magnetic shielding assemblies are provided inside the arc wall sections, and the second magnetic shielding assemblies are provided inside the straight wall sections.

[0013] The first magnetic shielding assembly includes a magnetic shielding metal sheet, a mounting base, and a sealing support pad. The magnetic shielding metal sheet is arranged in parallel in the mounting base. The mounting base is fixed to the inner side of the corresponding arc-shaped wall section of the fuel tank. A sealing support pad is provided between the bottom plate of the mounting base and the inner wall of the corresponding arc-shaped wall section of the fuel tank.

[0014] A water cooler and an oil draining system are provided on one side of the oil tank, and an oil storage tank is provided on the upper side of the oil tank.

[0015] The advantages and positive effects of this invention are as follows:

[0016] 1. This invention adopts a dual-path (dual-split) grid-side approach for each phase, with each path using a parallel connection of two cables to reduce the transformer grid-side voltage from 220kV to 66kV. This enables the power generated by the offshore wind turbine to be directly connected to the offshore platform via a 66kV three-phase cable. This direct connection eliminates the need for the original wind farm booster station configuration and also eliminates the need for three-phase cables, saving a significant amount of offshore AC cables. Furthermore, considering the insulation characteristics of the transformer, this invention can also boost the valve-side voltage to ±500kV.

[0017] 2. In order to ensure that the full through impedance of the valve-side coil and the first grid-side coil, the half through impedance of the valve-side coil and the second grid-side coil, and the split impedance matching between the first grid-side coil and the second grid-side coil are reasonable and meet the requirements of the split coefficient, this invention splits the grid-side winding coil into a first grid-side coil and a second grid-side coil in the radial direction. In addition, to eliminate the influence of higher harmonics, a balancing coil is added, thus forming an arrangement structure of "first grid-side coil, valve-side coil, second grid-side coil, and balancing coil" from the inside out. Compared with the prior art, this invention does not have a tap changer and does not have a voltage regulating coil, further simplifying the structure.

[0018] 3. This invention features a grid-side outlet box, a first grid-side neutral point bushing, a second grid-side neutral point bushing, a valve-side outlet box, a valve-side neutral point bushing, and a balance bushing on the oil tank to allow for the lead-out of the beginning and end of each coil. Considering the limited space on offshore platforms, this invention eliminates the 500kV test bushing. The valve-side center point withstand voltage test can be conducted using a neutral point GIS test bushing (valve-side neutral point bushing) on-site. Furthermore, to facilitate testing and reduce overall working time, test bushings are installed at both the grid-side beginning point (grid-side bushing) and the valve-side center point (valve-side neutral point bushing). This allows the three-phase transformer to undergo partial discharge and withstand voltage tests continuously in one operation.

[0019] 4. The tank walls on both sides of the oil tank of the present invention include staggered arc-shaped wall sections and straight wall sections. The arc-shaped wall sections are located on the outside of the corresponding coil assembly and have multiple sets of first magnetic shielding components evenly distributed on their inner walls. The straight wall sections are provided with second magnetic shielding components on their inner sides. This can fully ensure the magnetic shielding effect of the transformer tank. Furthermore, the width of the oil tank of the present invention is only the maximum width of the arc-shaped wall sections on both sides is the same as the width of the tank wall in the prior art, both being H1. The rest of the tank wall of the present invention is smaller than H1. Therefore, the present invention reduces the volume and weight of the tank compared to the prior art, thereby reducing the weight and volume of the connected transformer.

[0020] 5. The arc-shaped wall section of the fuel tank in this invention can be reinforced by the mounting base of the first magnetic shielding component. Therefore, no other reinforcing structure is needed on the outer wall of the arc-shaped wall section. At the same time, since the length of the straight wall section of the fuel tank is shortened, it is not necessary to set a large fuel tank reinforcing iron. A relatively small fuel tank reinforcing rib plate can ensure the strength of the fuel tank. This further reduces the weight of the fuel tank of this invention and also reduces the production cost. Attached Figure Description

[0021] Figure 1 This is a top view of the structure of the present invention.

[0022] Figure 2 for Figure 1 A schematic diagram of the internal winding arrangement of the present invention.

[0023] Figure 3 for Figure 2 A schematic diagram showing the connection relationship of the balancing coils of each phase.

[0024] Figure 4 for Figure 2 Enlarged schematic diagram of the arrangement of the middle balancing coil, valve-side coil, and second grid-side coil.

[0025] Figure 5 for Figure 2 A schematic diagram showing the connection relationship of the first-phase coils in each phase.

[0026] Figure 6 for Figure 2 A schematic diagram showing the connection relationship of the second-phase coils in each phase.

[0027] Figure 7 for Figure 2 A schematic diagram showing the connection relationship of the valve-side coils of each phase.

[0028] Figure 8 for Figure 1 Enlarged view of point A in the image.

[0029] Figure 9 for Figure 8 Enlarged view of point B in the image.

[0030] Figure 10 for Figure 1 The I-direction view in the middle,

[0031] Figure 11 for Figure 10 Schematic diagram of the structure of the middle valve outlet box.

[0032] Figure 12 for Figure 1 Top view of the fuel tank.

[0033] Figure 12a for Figure 12 Diagram showing the usage status of the intermediate fuel tank.

[0034] Figure 12b for Figure 12a Enlarged schematic diagram of the arc-shaped wall section of the middle oil tank.

[0035] Figure 12c Figure 12b AA view in

[0036] Figure 12d This is a schematic diagram of a transformer tank structure in the prior art.

[0037] Figure 13 This is a schematic diagram of the two-way split wiring principle of the present invention.

[0038] Among them, 1 is the first grid-side coil, 2 is the valve-side coil, 3 is the second grid-side coil, 4 is the balancing coil, 5 is the grid-side bushing, 6 is the grid-side AC cable, 7 is the valve-side bushing, 8 is the valve-side DC cable, 9 is the oil tank, 901 is the arc-shaped wall section of the oil tank, 902 is the straight wall section of the oil tank, 903 is the clamp, 904 is the first magnetic shielding assembly, 9041 is the magnetic shielding metal sheet, 9042 is the sealing support pad, 9043 is the base plate, 9044 is the first side plate, 9045 is the second side plate, 905 is the oil tank reinforcing rib plate, 906 is the oil tank lifting plate, and 907 is the transport shoulder. 908 is the tank wall, 909 is the tank side reinforcing rib, 910 is the second magnetic shielding assembly, 911 is the reinforcing iron, 10 is the tank magnetic shield, 11 is the iron core, 1101 is the core column, 1102 is the side column, 12 is the balance coil electrostatic plate, 13 is the balance coil corner ring, 14 is the balance sleeve, 15 is the valve side neutral point sleeve, 1601 is the first grid side neutral point sleeve, 1602 is the second grid side neutral point sleeve, 17 is the water cooler, 18 is the oil tank, 19 is the grid side outlet box, 20 is the valve side outlet box, 21 is the control cabinet, and 22 is the oil drainage system. Detailed Implementation

[0039] The invention will now be described in further detail with reference to the accompanying drawings.

[0040] like Figures 1-13 As shown, the present invention includes an oil tank 9 and an iron core 11 disposed within the oil tank 9, wherein... Figure 2 As shown, each phase core column 1101 of the iron core 11 is fitted with a coil assembly, and the coil assembly includes a first grid-side coil 1, a valve-side coil 2, a second grid-side coil 3, and a balance coil 4 arranged sequentially from the inside to the outside. Figures 5-6 As shown, the beginning of each phase's first grid-side coil 1 and the beginning of each phase's second grid-side coil 3 are connected to two parallel grid-side AC cables 6. The ends of each phase's first grid-side coil 1 and the ends of each phase's second grid-side coil 3 are all connected together, as shown. Figure 7As shown, the first end of each phase valve-side coil 2 is connected to the corresponding valve-side DC cable 8, and the ends of each phase valve-side coil 2 are connected together. Additionally, as shown... Figure 3 As shown, the phase balancing coils 4 are connected in sequence.

[0041] like Figure 13 As shown, firstly, to reduce the transformer grid-side voltage to 66kV, this invention employs a dual-input method for the coil assembly, that is, splitting the grid-side winding coil into a first grid-side coil 1 and a second grid-side coil 3. Secondly, to ensure reasonable matching of the full-through impedance between the valve-side coil 2 and the first grid-side coil 1, the half-through impedance between the valve-side coil 2 and the second grid-side coil 3, and the split impedance matching between the first grid-side coil 1 and the second grid-side coil 3, and to meet the split coefficient requirements, this invention splits the grid-side winding coil into a first grid-side coil 1 and a second grid-side coil 3 radially, and arranges the first grid-side coil 1, valve-side coil 2, and second grid-side coil 3 in an order from the inside out. Thirdly, to eliminate the influence of higher-order harmonics, this invention adds a balancing coil 4, and simultaneously checks the impedance of the balancing coil 4 to the grid-side and valve-side coils to meet the short-circuit capability requirements between the various coils of the transformer, thus forming the following... Figure 2 The arrangement of the coils from the inside out, namely "first grid-side coil 1, valve-side coil 2, second grid-side coil 3, and balancing coil 4", is shown. Compared to existing technologies, this invention does not include a tap changer or a voltage regulating coil. Furthermore, since the coil voltage of this invention is ±500kV, the influence of the voltage transmitted through the valve-side coil 2 on the balancing coil 4 is considered. Figure 4 As shown, the present invention increases the distance X between the second mesh side coil 3 and the balancing coil 4, and adds a balancing coil electrostatic plate 12 and a balancing coil corner ring 13 to the balancing coil 4 for protection, wherein the balancing coil electrostatic plate 12 is located at the end of the balancing coil 4, and the balancing coil corner ring 13 is located on the upper side of the balancing coil electrostatic plate 12.

[0042] like Figure 1 and Figures 8-11 As shown, the oil tank 9 is equipped with a wire-side outlet box 19, a first wire-side neutral point bushing 1601, and a second wire-side neutral point bushing 1602, wherein... Figures 5-6 and Figures 9-10 As shown, the grid-side outlet box 19 is equipped with a grid-side sleeve 5, and the starting ends of the first grid-side coil 1 of each phase and the starting ends of the second grid-side coil 3 of each phase are respectively connected to two parallel grid-side AC cables 6 introduced into the grid-side outlet box 19 through the grid-side sleeve 5 in the corresponding grid-side outlet box 19. Figures 5-6 and Figure 8 As shown, the ends of the first grid-side coils 1 of each phase are connected together and led out from the first grid-side neutral point sleeve 1601, and the ends of the second grid-side coils 3 of each phase are connected together and led out from the second grid-side neutral point sleeve 1602.

[0043] like Figure 1 As shown, the first network-side neutral point bushing 1601 and the second network-side neutral point bushing 1602 are respectively located at both ends of the oil tank 9, and each network-side outlet box 19 is located between the first network-side neutral point bushing 1601 and the second network-side neutral point bushing 1602.

[0044] like Figure 1 and Figures 8-11 As shown, the oil tank 9 is equipped with a valve-side outlet box 20 and a valve-side neutral point bushing 15, wherein... Figure 7 and Figures 10-11 As shown, the valve-side outlet box 20 is equipped with a valve-side sleeve 7, and the first end of each phase valve-side coil 2 is connected to the valve-side DC cable 8 introduced into the valve-side outlet box 20 through the corresponding valve-side sleeve 7 in the valve-side outlet box 20. Figure 1 and Figure 7 As shown, the ends of the valve-side coils 2 of each phase are connected together and led out from the valve-side neutral point bushing 15.

[0045] like Figure 1 As shown, a water cooler 17 and an oil drain system 22 are provided on one side of the oil tank 9, and the valve-side neutral point sleeve 15 is located on the side of the oil tank 9 near the water cooler 17. The water cooler 17 and the oil drain system 22 are technologies known in the art.

[0046] like Figure 1 and Figures 8-11 As shown, the oil tank 9 is equipped with a balance sleeve 14, and as Figure 3 As shown, in this embodiment, the B-phase balancing coil 402 is wound to the left, and the A-phase balancing coil 401 and the C-phase balancing coil 403 are wound to the right. The end Wx of the A-phase balancing coil 401 is connected to the beginning Wb of the B-phase balancing coil 402, and the end Wy of the B-phase balancing coil 402 is connected to the beginning Wc of the C-phase balancing coil 403. The beginning Wa of the A-phase balancing coil 401 and the end Wz of the C-phase balancing coil 403 are respectively led out from the corresponding balancing sleeves 14 on the oil tank 9.

[0047] like Figure 1 As shown, the balance sleeve 14 is located on the side of the oil tank 9 away from the water cooler 17, and each valve-side outlet box 20 is located between the balance sleeve 14 and the valve-side neutral point sleeve 15.

[0048] like Figure 5As shown, in this embodiment, the first end A1 of the A-phase first grid-side coil 101 is connected to the parallel grid-side AC cables A11 and A12; the first end B1 of the B-phase first grid-side coil 102 is connected to the parallel grid-side AC cables B11 and B12; and the first end C1 of the C-phase first grid-side coil 103 is connected to the parallel grid-side AC cables C11 and C12. The ends X1 of the A-phase first grid-side coil 101, Y1 of the B-phase first grid-side coil 102, and Z1 of the C-phase first grid-side coil 103 converge at the neutral point O1. Figure 8 As shown, the cable leading from the neutral point 01 is led out through the first network-side neutral point sleeve 1601. Similarly, as... Figure 6 As shown, the first end A2 of the second grid-side coil 301 of phase A is connected to the parallel grid-side AC cables A21 and A22; the first end B2 of the second grid-side coil 302 of phase B is connected to the parallel grid-side AC cables B21 and B22; and the first end C2 of the second grid-side coil 303 of phase C is connected to the parallel grid-side AC cables C21 and C22. The ends X2 of the second grid-side coil 301 of phase A, Y2 of the second grid-side coil 302 of phase B, and Z2 of the second grid-side coil 303 of phase C converge at the neutral point O2. Figure 8 As shown, the cable leading from the neutral point 02 is led out through the second network-side neutral point sleeve 1602.

[0049] like Figure 7 As shown, the first end a of phase A valve-side coil 201, the first end b of phase B valve-side coil 202, and the first end c of phase C valve-side coil 203 are respectively connected to the corresponding valve-side DC cables 8. The ends x of phase A valve-side coil 201, y of phase B valve-side coil 202, and z of phase C valve-side coil 203 converge at the neutral point O, and as shown... Figure 1 As shown, the cable leading from the neutral point O is led out through the valve-side neutral point sleeve 15.

[0050] like Figure 12 As shown, the tank wall 908 of the oil tank 9 is provided with an arc-shaped wall section 901, and a magnetic shield 10 is provided on the arc-shaped wall section 901. In this invention, the arc-shaped wall section 901 structure is locally used at the point where the center line of each coil assembly is closest to the tank wall of the oil tank 9, and a magnetic shield 10 is provided on the arc-shaped wall section 901 according to the leakage magnetic field distribution. This ensures the reliability of the product's insulation and mechanical structures while minimizing installation dimensions and overall weight. Specifically:

[0051] like Figure 12aAs shown, in this embodiment, the tank wall 908 includes staggered arc-shaped wall sections 901 and straight wall sections 902. The arc-shaped wall sections 901 are located on the outside of the corresponding coil assembly, and the arc shape of the arc-shaped wall sections 901 matches the outer arc shape of the corresponding coil assembly. The magnetic shield 10 includes a first magnetic shielding component 904 and a second magnetic shielding component 910. Multiple sets of first magnetic shielding components 904 are provided on the inner side of the arc-shaped wall sections 901, and as shown... Figures 12b-12c As shown, the first magnetic shielding assembly 904 includes a magnetic shielding metal sheet 9041, a mounting base, and a sealing support pad 9042. The magnetic shielding metal sheets 9041 are arranged side-by-side in the mounting base. The mounting base is fixed to the inner side of the corresponding arc-shaped wall section 901 of the fuel tank. A sealing support pad 9042 is provided between the base plate 9043 of the mounting base and the inner wall of the corresponding arc-shaped wall section 901 of the fuel tank. Figure 12a As shown, a second magnetic shielding component 910 is provided on the inner side of the straight wall section 902 of the oil tank. In this embodiment, the second magnetic shielding component 910 can adopt the same structure as the first magnetic shielding component 904. In addition, in this embodiment, the magnetic shielding metal sheet 9041 is a silicon steel sheet.

[0052] like Figure 12a As shown, the width of the fuel tank 9 of the present invention comprises two parts, wherein the maximum width of the arc-shaped wall sections 901 on both sides of the fuel tank is H1, and the width of the straight wall sections 902 on both sides of the fuel tank is H2, and H2 is less than H1. Figure 12d As shown, the width of the oil tank in the prior art is the same as the maximum width of the arc-shaped wall sections 901 on both sides of the oil tank in this invention, both being H1. Therefore, compared with the prior art, this invention reduces the volume and weight of the oil tank 9, thereby reducing the weight and volume of the connecting transformer and also reducing the cost of the offshore flexible DC platform. According to actual production calculations, generally, large-capacity offshore flexible DC connecting transformers using the structure of this invention can reduce the weight of transformer oil and steel plates by approximately 1.5 tons. Additionally, as... Figures 12b-12c As shown, the present invention utilizes a sealing support pad 9042 to ensure that the central axis of each group of first magnetic shielding components 904 is aligned with the arc center of the arc wall section 901 of the oil tank. At the same time, each group of first magnetic shielding components 904 is evenly arranged on the corresponding arc wall section 901 of the oil tank, thereby ensuring the magnetic shielding effect of the arc wall section 901 of the oil tank, and thus ensuring the magnetic shielding effect of the entire transformer oil tank 9 after the structural shape is changed.

[0053] like Figures 12b-12cAs shown, in this embodiment, the mounting base includes a first side plate 9044 and a second side plate 9045. The two first side plates 9044 are respectively disposed on the left and right sides of the base plate 9043, and the two second side plates 9045 are respectively disposed on the front and rear sides of the base plate 9043. The magnetic shielding metal sheet 9041 is disposed in the cavity formed by the first side plate 9044, the second side plate 9045, and the base plate 9043. In this embodiment, the magnetic shielding metal sheet 9041, the first side plate 9044, the second side plate 9045, and the base plate 9043 can be welded together to form a whole. At the same time, the mounting base formed by the first side plate 9044, the second side plate 9045, and the base plate 9043 is welded and fixed to the corresponding arc wall section 901 of the fuel tank. Then, the sealing support pad 9042 is inserted into the gap between the base plate 9043 and the arc wall section 901 of the fuel tank to press the arc wall sections 901 of the fuel tank on both sides and the mounting base tightly. like Figure 12d As shown, in the prior art, since the tank walls on both sides of the tank 9 are entirely straight, and in order to ensure strength, it is necessary to provide block-shaped or strip-shaped reinforcing iron 911 on the tank walls on both sides of the tank 9. Figure 12a As shown, the fuel tank wall of the present invention adopts a structure in which the arc-shaped wall section 901 and the straight wall section 902 are alternately arranged. Multiple sets of first magnetic shielding components 904 are provided on the inner side of the arc-shaped wall section 901, and the mounting base of the first magnetic shielding component 904 can provide reinforcement. Therefore, no other reinforcing structure is needed on the outer wall of the arc-shaped wall section 901. Simultaneously, because the length of the straight wall section 902 is shortened, it does not need to be equipped with a large reinforcing iron 911; instead, the strength of the fuel tank 9 is ensured by providing fuel tank reinforcing ribs 905. This reduces the weight of the fuel tank 9 of the present invention and also reduces production costs. To further ensure the strength of the fuel tank 9, fuel tank side reinforcing ribs 909 are provided on the side plates at both ends of the fuel tank 9.

[0054] like Figure 2 As shown, the iron core 11 has a three-phase five-column structure, in which the three central columns 1101 are fitted with coil assemblies, and the side columns 1102 on both sides serve as magnetic flux circuits without coils.

[0055] like Figure 1 and Figure 10 As shown, an oil storage tank 18 is provided on the upper side of the oil tank 9, and the oil storage tank 18 is a technology known in the art.

[0056] In addition, due to insufficient space on the offshore platform, the 500kV test bushing is eliminated. The withstand voltage test at the valve side center point is conducted through the on-site neutral point GIS test bushing (valve side neutral point bushing 15). Furthermore, to facilitate testing and reduce the total working time, test bushings are installed at both the grid side head end (grid side bushing 5) and the valve side center point (valve side neutral point bushing 15). This allows the three-phase transformer to undergo partial discharge and withstand voltage tests continuously at one time.

[0057] The working principle of this invention is as follows:

[0058] like Figure 13 As shown, to reduce the transformer grid-side voltage to 66kV, this invention employs a dual-input method, splitting the grid-side winding coil into a first grid-side coil 1 and a second grid-side coil 3. To ensure reasonable impedance matching between the valve-side coil 2 and the first grid-side coil 1, the valve-side coil 2 and the second grid-side coil 3, and the split impedance matching between the first grid-side coil 1 and the second grid-side coil 3, and to meet the splitting coefficient requirements, this invention radially splits the grid-side winding coil into the first grid-side coil 1 and the second grid-side coil 3. The transformer connection group of this invention is YNYNyn0+d, and a balancing coil 4 is added to eliminate the influence of higher harmonics. This invention does not include a tap changer or a voltage regulating coil, and the power generated by the offshore wind turbine is directly connected to the offshore platform via a 66kV three-phase cable. This eliminates the need for the original wind farm booster station configuration and also eliminates the need for three-phase cables. This direct connection method saves a significant amount of offshore AC cables. Furthermore, considering the transformer's insulation characteristics, this invention can also boost the valve-side voltage to ±500kV.

[0059] Other examples Figures 7-11 As shown, this invention provides a grid-side outlet box 19, a first grid-side neutral point bushing 1601, a second grid-side neutral point bushing 1602, a valve-side outlet box 20, a valve-side neutral point bushing 15, and a balance bushing 14 on the oil tank 9 to achieve the lead-out of the beginning and end of each coil. Considering the limited space on offshore platforms, this invention eliminates the 500kV test bushing; the valve-side center point withstand voltage test can be conducted using the on-site neutral point GIS test bushing (valve-side neutral point bushing 15). Furthermore, for testing purposes… To facilitate and reduce the overall working time, test bushings are installed at the first end of the grid side (grid side bushing 5) and the center point of the valve side (valve side neutral point bushing 15). This allows the three-phase transformer to undergo partial discharge and withstand voltage tests continuously at one time. At the same time, the present invention uses an arc-shaped section of the tank wall at the point where the center line of the transformer body is closest to the tank wall of the oil tank 9. According to the leakage magnetic field distribution, a magnetic shield 10 is welded on the arc-shaped section of the tank wall. In this way, while ensuring the reliability of the product's insulation structure and mechanical structure, the installation size and overall weight are reduced as much as possible.

Claims

1. A three-phase split transformer for ±500kV offshore wind power flexible DC transmission, characterized in that: The system includes an oil tank (9) and an iron core (11) located within the oil tank (9). Each phase core column (1101) of the iron core (11) is fitted with a coil assembly, which includes a first grid-side coil (1), a valve-side coil (2), a second grid-side coil (3), and a balance coil (4) arranged sequentially from the inside to the outside. The oil tank (9) is equipped with a grid-side outlet box (19), a first grid-side neutral point bushing (1601), a second grid-side neutral point bushing (1602), a valve-side outlet box (20), a valve-side neutral point bushing (15), and a balance bushing (14). The first grid-side coil (1) of each phase and the second grid-side coil (3) of each phase are connected at the beginning of the circuit. Each phase is introduced into the corresponding grid-side outlet box (19) and connected to the corresponding two parallel grid-side AC cables (6). The ends of the first grid-side coils (1) of each phase are connected and led out from the first grid-side neutral point bushing (1601). The ends of the second grid-side coils (3) of each phase are connected and led out from the second grid-side neutral point bushing (1602). The first end of each phase valve-side coil (2) is introduced into the corresponding valve-side outlet box (20) and connected to the corresponding valve-side DC cable (8). The ends of each phase valve-side coil (2) are connected and led out from the valve-side neutral point bushing (15). The balance coils of each phase are connected end to end in sequence and led out from the corresponding balance bushings (14) at both ends.

2. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The grid-side outlet box (19) is provided with a grid-side sleeve (5), and the first end of each phase first grid-side coil (1) and the first end of each phase second grid-side coil (3) are respectively connected to two parallel grid-side AC cables (6) introduced into the grid-side outlet box (19) through the grid-side sleeve (5) in the corresponding grid-side outlet box (19).

3. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The first network-side neutral point bushing (1601) and the second network-side neutral point bushing (1602) are respectively located at both ends of the oil tank (9), and each network-side outlet box (19) is located between the first network-side neutral point bushing (1601) and the second network-side neutral point bushing (1602).

4. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The valve-side outlet box (20) is provided with a valve-side bushing (7), and the first end of each phase valve-side coil (2) is connected to the valve-side DC cable (8) introduced into the valve-side outlet box (20) through the valve-side bushing (7) in the corresponding valve-side outlet box (20).

5. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The balancing coil (4) is provided with a balancing coil electrostatic plate (12) and a balancing coil corner ring (13), wherein the balancing coil electrostatic plate (12) is located at the end of the balancing coil (4), and the balancing coil corner ring (13) is located on the upper side of the balancing coil electrostatic plate (12).

6. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The phase balancing coils are connected end to end in sequence, and the beginning of the phase A balancing coil (401) and the end of the phase C balancing coil (403) are respectively led out from the corresponding balancing sleeve (14) on the oil tank (9).

7. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The oil tank (9) has an arc-shaped wall section (901) on its tank wall (908), and a magnetic shield (10) is provided on the arc-shaped wall section (901).

8. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 7, characterized in that: The tank wall (908) includes staggered arc wall sections (901) and straight wall sections (902), with the arc wall sections (901) located on the outside of the corresponding coil assembly. The magnetic shield (10) includes a first magnetic shield assembly (904) and a second magnetic shield assembly (910), wherein multiple sets of first magnetic shield assemblies (904) are provided on the inner side of the arc wall section (901), and a second magnetic shield assembly (910) is provided on the inner side of the straight wall section (902).

9. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 8, characterized in that: The first magnetic shielding assembly (904) includes a magnetic shielding metal sheet (9041), a mounting base, and a sealing support pad (9042). The magnetic shielding metal sheet (9041) is arranged in parallel in the mounting base. The mounting base is fixed to the inner side of the corresponding arc wall section (901) of the oil tank. A sealing support pad (9042) is provided between the bottom plate (9043) of the mounting base and the inner wall of the corresponding arc wall section (901) of the oil tank.

10. The three-phase split transformer for ±500kV offshore wind power flexible DC transmission according to claim 1, characterized in that: The oil tank (9) is provided with a water cooler (17) and an oil draining system (22) on one side, and an oil storage tank (18) is provided on the upper side of the oil tank (9).

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