Offshore wind power transformer low-voltage lead and wiring method

Abstract

The invention discloses a low-voltage lead of an offshore wind power transformer and a wiring method, and belongs to the field of structural design of the low-voltage lead of the offshore wind power transformer, the low-voltage lead mainly comprises four copper stranded wires and an outer wrapping insulating layer, the four copper stranded wires are stranded, and the outer side of the four stranded copper stranded wires is tightly wrapped by the outer wrapping insulating layer; the upper ends of the first copper stranded wire and the second copper stranded wire are led out of an outer wrapping insulating layer through a first wiring terminal, and the upper ends of the third copper stranded wire and the fourth copper stranded wire are led out of an outer wrapping insulating layer through a second wiring terminal. And the lower ends of the four copper stranded wires are not stranded and are exposed out of the outer insulating layer. Two low-voltage leads are adopted, and wiring terminals of the two low-voltage leads are respectively connected with the two groups of low-voltage sleeves through tail sleeves; and the exposed copper stranded wires of the two low-voltage leads are correspondingly connected through a third wiring terminal. The circulating current problem can be avoided, and the loss is reduced; mechanical strength of the low-voltage lead is enhanced, and deformation and movement of the lead are prevented; and the wiring space of the low-voltage lead and the clamping difficulty of the lead can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of low-voltage lead structure design for offshore wind power transformers, and in particular to a low-voltage lead for offshore wind power transformers and a wiring method thereof. Background Art

[0002] Traditional energy sources are highly polluting and have limited reserves. Wind energy, as a clean and renewable energy source, is widely used in renewable energy generation. Offshore wind resources are abundant (annual average wind speed ≥8m / s), with stable wind speeds higher than onshore, providing a foundation for the development of offshore wind power. With technological advances, the capacity of individual wind turbines has continued to increase, from the initial megawatt level to tens of megawatts, and installation depths have also expanded from shallow waters to deep seas. With innovations in transmission technology, offshore wind power has been able to be stably connected to the grid. New offshore wind power transformers have emerged, featuring high resistance to corrosion, humidity, and vibration. Designed for a lifespan of at least 25 years, they provide a solid foundation for the stable transmission and efficient operation of offshore wind farms.

[0003] In wind power generation systems, onshore wind turbines have exceeded 10MW, and offshore turbines are on their way to 20MW. However, the voltage of the generators on the power generation side is generally 0.69kV / 1.14kV / 1.35kV, which drives the current on the low-voltage side of the transformer to over 10,000A. Traditional low-voltage leads are primarily copper busbars and copper stranded wire. Low-voltage coils are typically wound with copper foil. To withstand a current of 10,000A, the total thickness of the copper foil is generally greater than 3.5mm. This makes coil size difficult to control and leads to large size deviations in the copper busbars leading out of the coils. During lead assembly, using copper busbars for connection often results in installation difficulties due to problems with the fit between the lead and the clamp. In contrast, copper stranded wire, due to its excellent flexibility, can accommodate minor deviations during assembly to a certain extent, making installation more convenient, making it a common choice.

[0004] During the design of low-voltage leads, copper stranded wire connects the transformer's low-voltage bushing and coil. As low-voltage current increases, multiple stranded wires are often required in parallel. Due to the different locations of the low-voltage coil outlet and the bushing connection point, the copper stranded wires have varying lengths and conductor resistance. Due to the complex magnetic field within the transformer, current passing through the magnetic field is subject to the Lorentz force, which acts differently on copper stranded wires at different locations, causing current redistribution and circulating currents, increasing lead losses. Multiple copper stranded wires carrying the same current attract each other. If the currents are inconsistent, the resulting force is unbalanced, causing lead deformation and, in severe cases, threatening the safe operation of the transformer. Furthermore, insulated copper stranded wires are difficult to secure, occupying a large space and making lead clamping difficult. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art of the low-voltage lead of an offshore wind power transformer, such as the uneven current distribution among the copper strands, the mutual attraction of multiple copper strands with current in the same direction, the difficulty in fixing a single copper strand with external insulation, and the difficulty in clamping the lead, and to provide a low-voltage lead and wiring method for an offshore wind power transformer. To achieve this purpose, the present invention adopts the following technical solution: the low-voltage lead includes: a first copper stranded wire, a second copper stranded wire, a third copper stranded wire, a fourth copper stranded wire and an outer insulating layer. The first copper stranded wire, the second copper stranded wire, the third copper stranded wire and the fourth copper stranded wire are twisted to form an integral structure, and the outer insulating layer is tightly wrapped around the outside of the four twisted copper stranded wires; wherein, the upper ends of the first copper stranded wire and the second copper stranded wire are led out of the outer insulating layer by the first wiring terminal, and the upper ends of the third copper stranded wire and the fourth copper stranded wire are led out of the outer insulating layer by the second wiring terminal; the lower ends of the first copper stranded wire, the second copper stranded wire, the third copper stranded wire and the fourth copper stranded wire are not twisted and the outer insulating layer is exposed.

[0006] A further improvement of the present technical solution is that the first copper stranded wire, the second copper stranded wire, the third copper stranded wire and the fourth copper stranded wire are twisted in a centrally symmetrical spiral manner, and the four copper stranded wires are periodically cross-changed during the twisting process. A further improvement of the present technical solution is that the four twisted copper strands are of the same length. According to the twisting method, pitch, and spiral length parameters of the copper strands, the original length required for each copper strand before twisting is calculated to achieve the same length of the four twisted copper strands. The calculation method is as follows:

[0007]

[0008] Where, k is the twist-in coefficient, d is the outer diameter of each copper strand, h is the pitch, L is the spiral length, L 0 is the original length of the twisted portion of the copper wire.

[0009] A further improvement of the technical solution is that the twisting pitch of the copper stranded wire is 8-12 times the outer diameter of a single copper stranded wire.

[0010] A further improvement of the technical solution is that the outer insulation layer uses corrosion-resistant, high and low temperature resistant insulation tape or insulation paint.

[0011] A further improvement of the technical solution is that the thickness of the outer insulating layer is 2-3 mm.

[0012] A further improvement of the technical solution is that the lengths of the parts extending from the upper ends of the four copper strands are consistent, and the lengths of the parts extending from the lower ends are consistent.

[0013] A further improvement of the technical solution is that the axes and surrounding areas of the four copper strands are fixed with glass fiber rods.

[0014] A further improvement of the present technical solution includes a wiring method for the low-voltage leads of an offshore wind power transformer, comprising: using two low-voltage leads, connecting the wiring terminals of the two low-voltage leads to two groups of low-voltage bushings through tail bushings respectively; and connecting the exposed copper strands of the two low-voltage leads to corresponding connections through a third wiring terminal.

[0015] A further improvement of the technical solution is that the connection between the wiring terminal and the copper stranded wire is achieved by cold pressing or welding, and the wiring terminal and the low-voltage bushing are fixedly connected by bolts.

[0016] It can be seen from the above technical solutions that the present invention has the following beneficial effects: by twisting four copper strands together, the structure enhances the mechanical strength of the conductors, forming a more stable overall structure, effectively avoiding the deformation and discharge risks caused by external forces such as vibration and impact that are common in offshore wind power scenarios, improving the transformer's ability to resist short circuits, and ensuring the safe and stable operation of the transformer. The four copper strands are uniformly wrapped with an insulating layer, which reduces the wiring space, facilitates the compact design of the transformer, reduces the difficulty of lead clamping, and improves the convenience of overall production and assembly; reduces the potential risk of errors caused by complex operations during the assembly process, helps to ensure product quality, and promotes the large-scale production and application of offshore wind power transformers. The twisted parts of the four copper strands are of the same length, the upper lead-out parts of the low-voltage leads are of the same length, and the lower lead-out parts are of the same length, which reduces the current unevenness caused by resistance and magnetic field, can avoid circulating current, and reduce lead loss; the current magnitude between the four copper strands is consistent, the force is evenly distributed, and the deformation of the low-voltage leads is effectively avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of the low-voltage lead connection method of the offshore wind power transformer of the present invention.

[0019] Figure 2 This is a stress analysis diagram of the twisted copper wire during the operation of the transformer of the present invention.

[0020] Figure 3This is a cross-sectional view of four copper strands wrapped with an insulation layer after being twisted together according to the present invention.

[0021] Figure 4 This is a schematic diagram of the connection of four parallel copper strands of a traditional low-voltage lead.

[0022] Figure 5 This is a force analysis diagram of the two wires of a traditional low-voltage lead after being energized.

[0023] Figure 6 This is a cross-sectional view of a single stranded wire of a traditional low-voltage lead wire after being wrapped with an insulation layer.

[0024] In the figure, 1, the first low-voltage lead, 2, the second low-voltage lead, 101, the first copper stranded wire, 102, the second copper stranded wire, 103, the third copper stranded wire, 104, the fourth copper stranded wire, 201, the fifth copper stranded wire, 202, the sixth copper stranded wire, 203, the seventh copper stranded wire, 204, the eighth copper stranded wire, 110, the first copper stranded wire before twisting, 120, the second copper stranded wire before twisting, 130, the third copper stranded wire before twisting, 140, the fourth copper stranded wire before twisting, 210, the fifth copper strand before twisting, 220, the sixth copper strand before twisting, 230, the seventh copper strand before twisting, 240, the eighth copper strand before twisting, 3, left low-voltage bushing, 4, right low-voltage bushing, 5, tail bushing, 6, first terminal, 7, second terminal, 8, third terminal, 901, insulation layer wrapped around the copper strand after twisting, 902, insulation layer wrapped around a single copper strand before twisting, 10, copper busbar, 11, fiberglass rod. DETAILED DESCRIPTION

[0025] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions protected by the present invention will be clearly and completely described below using specific embodiments and drawings. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of them. Based on the embodiments in this patent, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this patent.

[0026] Traditional offshore wind power transformer low voltage lead routing method reference Figure 4, the traditional low-voltage lead uses 8 300mm² copper strands. The first copper strand 110 before twisting, the second copper strand 120 before twisting, the third copper strand 130 before twisting, and the fourth copper strand 140 before twisting are connected in parallel and led out as a group; the fifth copper strand 210 before twisting, the sixth copper strand 220 before twisting, the seventh copper strand 230 before twisting, and the eighth copper strand 240 before twisting are connected in parallel and led out as a group. Due to the complex spatial layout of the transformer coil terminals and the bushing position, the actual length difference of the copper strands can reach more than 200mm, resulting in a DC resistance deviation of ≥5%. The magnetic field inside the transformer is unevenly distributed (the axial magnetic field intensity gradient reaches 0.1T / m). Due to the Lorentz force on the copper strands in the magnetic field, the copper strands at different positions are subjected to different forces, causing current redistribution. The measured current deviation between parallel copper strands is as high as 18%, and the proportion of circulating current loss in the total loss increases from 5% to 15%. Reference Figure 5 In traditional low-voltage leads, when the copper strands 110 and 120 are used in parallel, currents in the same direction flow in each copper strand. There is attraction between the copper strands with the same current direction. The uneven current will cause an imbalance in the resultant force (F1≠F2, and the resultant force will cause the conductor to deviate). In severe cases, the insulation layer will be broken down, increasing the risk of transformer operation. Figure 6 The traditional method of insulating and wrapping copper stranded wires is to insulate and wrap each single copper stranded wire separately. Multiple independent copper stranded wires require the design of multiple sets of independent clamping structures, making it difficult to fix the copper stranded wires with a single outer insulation layer, occupying a large space, low space utilization, and difficult to design the lead clamping.

[0027] Example 1: Now refer to Figure 1-3 Taking the actual application scenario of an offshore wind power transformer with a low-voltage current of 10,000 A as an example, the following description is given: the low-voltage lead includes a first copper strand 101, a second copper strand 102, a third copper strand 103, a fourth copper strand 104, and an outer insulating layer 901. The first copper strand 101, the second copper strand 102, the third copper strand 103, and the fourth copper strand 104 are twisted to form an integral structure, and the outer insulating layer 901 is tightly wrapped around the outside of the four twisted copper strands; the upper ends of the first copper strand 101 and the second copper strand 102 are led out of the outer insulating layer through the first terminal, and the upper ends of the third copper strand 103 and the fourth copper strand 104 are led out of the outer insulating layer through the second terminal; the lower ends of the first copper strand 101, the second copper strand 102, the third copper strand 103, and the fourth copper strand 104 are not twisted and the outer insulating layer is exposed.

[0028] In this embodiment, the first copper stranded wire 101, the second copper stranded wire 102, the third copper stranded wire 103, and the fourth copper stranded wire 104 are centrally symmetrically spirally twisted. During the twisting process, the four copper stranded wires are periodically cross-changed to ensure that the four copper stranded wires are evenly distributed.

[0029] In this embodiment, the four copper strands twisted together have the same length. Based on the twisting method, pitch, and spiral length parameters of the copper strands, the original length required for each copper strand before twisting is calculated to achieve the same length of the four copper strands twisted together. The calculation method is as follows:

[0030]

[0031] Where, k is the twist-in coefficient, d is the outer diameter of each copper strand, h is the pitch, L is the spiral length, L 0 is the original length of the twisted portion of the copper wire.

[0032] The twisted parts of the four copper strands are of the same length, which reduces the current unevenness caused by resistance and magnetic field, avoids circulating current, and reduces lead loss; the current between the four copper strands is consistent and the force is evenly distributed, which can effectively prevent deformation of the low-voltage lead.

[0033] In this embodiment, the twisting pitch of the copper stranded wire is 8-12 times the outer diameter of a single copper stranded wire. The ratio of the twisting pitch to the outer diameter is optimized, which ensures the tightness and regularity of the copper stranded wire during the twisting process, so that each copper stranded wire is evenly distributed in the overall structure after twisting, and there will be no local uneven density. At the same time, combined with the precise calculation of the consistency of the wire length, the electrical performance consistency of the four copper stranded wires is further enhanced. Due to the uniform current distribution, the influence of eddy current loss and skin effect is effectively reduced. The reduction of eddy current loss reduces the total energy loss during the transmission process, and the weakening of the skin effect ensures that the current can fully utilize the entire cross-sectional area of the copper stranded wire for transmission, rather than just concentrating on the surface, thereby improving the conductive efficiency of the low-voltage lead of the offshore wind power transformer. In this embodiment, the outer insulation layer 901 uses corrosion-resistant, high and low temperature resistant insulating tape or insulating paint. The insulating tape can isolate the conductor from contact with the outside world, prevent short circuit or leakage caused by water vapor, salt spray, etc., improve the insulation strength of the low-voltage lead, reduce friction or stretching damage caused by vibration of the lead, and protect the outer skin of the wire from mechanical stress damage; after the insulating paint (such as epoxy resin paint, acrylic paint) is applied to the surface of the twisted copper wire, a continuous and dense insulating film is formed, which can significantly improve the withstand voltage level of the outer insulation of the wire, especially maintain stable insulation resistance in a humid environment.

[0034] In this embodiment, the thickness of the outer insulation layer 901 is 2-3 mm. From the perspective of electrical insulation, a thickness of 2-3 mm can provide reliable insulation protection for the low-voltage leads of offshore wind power transformers, effectively preventing the occurrence of electrical faults such as current leakage, short circuit, and corona discharge. At the same time, under the premise of meeting insulation requirements, this thickness helps to reduce the radial space occupied. Offshore wind power transformers usually need to be laid out and designed within a limited space. The thinner thickness of the outer insulation layer 901 frees up the wiring space inside the transformer, thereby facilitating the rational arrangement of other components and leads, and is conducive to improving the overall compactness and integration of the transformer. The thinner thickness of the outer insulation layer 901 also helps to reduce material costs and production costs, and improves the economic benefits of offshore wind power transformers while ensuring their performance and safety.

[0035] like Figure 1 As shown, the lead-out parts of the copper stranded wires are spatially distributed. The lengths of the parts leading out of the upper ends of the four copper stranded wires are consistent, and the lengths of the parts leading out of the lower ends are consistent, thereby ensuring the symmetry and uniformity of the entire copper stranded wire loop, and at the same time ensuring the consistency of the copper stranded wire resistance, thereby making the current flowing through each copper stranded wire the same.

[0036] like Figure 3 As shown, in order to achieve the stable fixation and insulation requirements of the low-voltage lead of the offshore wind power transformer, the axis and surrounding areas of the four copper strands are fixed with glass fiber rods 11. Glass fiber itself has good mechanical properties, and its tensile strength is as high as ≥3000MPa. This high strength property enables the glass fiber rod to effectively resist various mechanical stresses that may occur during operation, such as electromagnetic force, vibration, etc.; at the same time, the glass fiber rod also has a high elastic modulus (≥70GPa), and can maintain its own size and shape stability when facing environmental changes such as thermal expansion and contraction, and will not affect the fixation effect of the copper strands due to deformation; even in the harsh environment of the offshore wind power transformer, such as high humidity, high salt fog and frequent vibration, the glass fiber rod can still be stable for a long time. The fiberglass rod supports the copper strands, ensuring their position remains unchanged and avoiding electrical failures caused by displacement of the copper strands. The fiberglass rod plays an important insulating role between the four copper strands. During the operation of the transformer, the copper strands will generate electromagnetic force and thermal stress due to the passage of current. The insulating properties of the fiberglass rod can effectively isolate these stresses and prevent short circuits or corona discharges between different copper strands or between copper strands and other components. Its good corrosion resistance enables it to maintain its insulation performance in a high salt spray marine environment, ensuring the long-term safe operation of the transformer. The fiberglass rod also has strong flame retardant properties.

[0037] Example 2: Reference Figure 1Taking the actual application scenario of an offshore wind power transformer with a low-voltage current of 10,000A as an example, the following is described: A wiring method for the low-voltage lead of an offshore wind power transformer uses two low-voltage leads, and the wiring terminals of the two low-voltage leads are respectively connected to the two groups of low-voltage bushings through the tail bushing 5; the exposed copper strands of the two low-voltage leads are correspondingly connected through the third wiring terminal 8.

[0038] like Figure 2 As shown, the force analysis of the four twisted copper wires during the operation of the existing offshore wind power transformer is shown. The four copper wires are twisted in a centrally symmetrical spiral manner. After the first copper wire 101, the second copper wire 102, the third copper wire 103, and the fourth copper wire 104 are twisted and uniformly wrapped with an insulating layer 901, according to the Ampere force principle, currents in the same direction produce the same attractive force, and the forces on different strands cancel each other out. The sum of the attractive forces between the first copper wire 101, the second copper wire 102, the third copper wire 103, and the fourth copper wire 104 is 0 (F 12 =F 21 、F 13 =F 31 、F 14 =F 41 、F 23 =F 32 、F 24 =F 42 、F 34 =F 43 This force balance ensures that the low-voltage lead 1 remains stable during operation and prevents displacement. It also optimizes the magnetic field distribution, significantly reducing the impact of magnetic flux leakage on the current of each conductor. Due to the uniform distribution of magnetic flux leakage, the electromagnetic interference experienced by each copper strand is consistent, achieving nearly equal current distribution. This reduces local overheating and losses caused by uneven current flow, thereby improving the efficiency and stability of power transmission. Furthermore, twisting significantly enhances the mechanical strength of the conductors, enabling them to effectively withstand the vibration and impact forces common in offshore wind power scenarios. This prevents the risk of discharge caused by insulation damage, changes in conductor spacing, or deformation due to stress, thereby improving transformer safety.

[0039] In this embodiment, when a short circuit occurs on the low-voltage side of an offshore wind turbine transformer, the instantaneous Ampere force on a single copper strand can reach 500N. However, because the vector sum of the first copper strand 101, the second copper strand 102, the third copper strand 103, the fourth copper strand 104, or the fifth copper strand 201, the sixth copper strand 202, the seventh copper strand 203, and the eighth copper strand 204 is zero, the overall structure is subject only to uniformly distributed internal stress. In this embodiment, coupled with the low-inductance design of the copper strands, low-voltage leads 1 and 2 can withstand a continuous short-circuit current of 0.2s without deformation, improving short-circuit resistance by 40% compared to traditional structures.

[0040] like Figure 1 The figure shows a schematic diagram of a conventional low-voltage lead connection method for an offshore wind turbine transformer. The diagram primarily includes a first low-voltage lead 1 and a second low-voltage lead 2. The first low-voltage lead 1 is twisted together with a first copper strand 101, a second copper strand 102, a third copper strand 103, and a fourth copper strand 104, and then uniformly coated with an insulation layer. The second low-voltage lead 2 is twisted together with a fifth copper strand 201, a sixth copper strand 202, a seventh copper strand 203, and an eighth copper strand 204, and then uniformly coated with an insulation layer. The twist pitch is set at 8-12 times the outer diameter of the stranded wire to optimize electromagnetic performance and reduce eddy current losses and skin effect. After twisting, the outer insulation layer 901 is 2-3 mm thick and is made of corrosion-resistant and high- and low-temperature-resistant (-40°C to +120°C) insulating tape or varnish. This effectively resists corrosion in the offshore salt spray environment and offers high insulation strength (power frequency withstand voltage ≥ 30 kV / mm), ensuring electrical safety. The twisted pitch design ensures uniform current distribution, reduces current unevenness caused by resistance and magnetic fields, reduces lead loss, and improves transformer operating efficiency; the twisted structure improves the mechanical strength of the conductor, avoids the risk of discharge caused by conductor deformation and displacement, and enhances short-circuit resistance; unified insulation wrapping simplifies the production process, improves efficiency, reduces wiring space, and facilitates compact transformer design; the flexibility of copper strands reduces assembly difficulty and adapts to internal space layout.

[0041] In this embodiment, to ensure a more stable structure and a more secure connection for the transformer's low-voltage lead wires, the connection between the terminal block and the copper stranded wire in the low-voltage lead wire is achieved by cold-pressing or welding, and the terminal block and the low-voltage bushing are fixed together by bolts. Cold-pressing uses a specialized mold to apply high pressure to the terminal block and the copper stranded wire, tightly bonding them and creating plastic deformation between the metals. This prevents the wires from loosening or falling off due to vibration, allowing the contact resistance to be controlled below 50µΩ, reducing contact losses during current flow and avoiding local overheating. Welding achieves molecular-level connection through metallurgical bonding, ensuring long-term stability and further reducing contact resistance to below 30µΩ. This eliminates the risk of oxidation and is particularly suitable for use in high-humidity, salt-fog environments at sea. This reliable connection, combined with the electromagnetically balanced design of the twisted structure, reduces contact losses and enhances the mechanical connection strength of the low-voltage lead wire. In the event of a short circuit on the transformer's low-voltage side, the low-impedance connection achieved by cold-pressing or welding can quickly conduct the short-circuit current, preventing arc discharge at the connection point due to excessive resistance. When bolting the low-voltage bushing, bolts of uniform specifications and standardized hole design are used. It is compatible with general tools and supports non-destructive disassembly. When the low-voltage lead needs to be repaired or replaced, on-site personnel can quickly disassemble and reassemble it, effectively improving the maintainability of the offshore wind power transformer. The rigid connection structure fixed with bolts has excellent mechanical properties and can withstand the electric force during operation. Combined with the good mechanical strength of the twisted lead, it ensures that there is no terminal deformation or bolt loosening within 0.2s under short-circuit conditions, thereby ensuring the safe and stable operation of the transformer in all aspects.

[0042] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-voltage lead wire for an offshore wind power transformer, characterized in that: include: A first copper strand (101), a second copper strand (102), a third copper strand (103), a fourth copper strand (104) and an outer insulating layer (901), wherein the first copper strand (101), the second copper strand (102), the third copper strand (103) and the fourth copper strand (104) are twisted to form an integral structure, and the outer insulating layer (901) is tightly wrapped around the outside of the four twisted copper strands; wherein the upper ends of the first copper strand (101) and the second copper strand (102) are led out of the outer insulating layer through the first wiring terminal, and the upper ends of the third copper strand (103) and the fourth copper strand (104) are led out of the outer insulating layer through the second wiring terminal; and the lower ends of the first copper strand (101), the second copper strand (102), the third copper strand (103) and the fourth copper strand (104) are not twisted and the outer insulating layer is exposed.

2. The low-voltage lead of the offshore wind power transformer according to claim 1, characterized in that: The first copper stranded wire (101), the second copper stranded wire (102), the third copper stranded wire (103), and the fourth copper stranded wire (104) are twisted in a centrally symmetrical spiral manner, and the four copper stranded wires are periodically cross-changed during the twisting process.

3. The low-voltage lead of the offshore wind power transformer according to claim 1, characterized in that: The four twisted copper wires are of the same length. The original length of each copper wire before twisting is calculated based on the twisting method, pitch, and spiral length parameters of the copper wires to achieve the same length of the four twisted copper wires. The calculation method is as follows: Where, k is the twist-in coefficient, d is the outer diameter of each copper strand, h is the pitch, L is the spiral length, L 0 is the original length of the twisted portion of the copper wire.

4. The low-voltage lead of the offshore wind power transformer according to claim 3, characterized in that: The twisting pitch of the copper stranded wire is 8-12 times the outer diameter of a single copper stranded wire.

5. The low-voltage lead of the offshore wind power transformer according to claim 1, characterized in that: The outer insulation layer (901) uses corrosion-resistant, high and low temperature resistant insulation tape or insulation paint.

6. The low-voltage lead of the offshore wind power transformer according to claim 5, characterized in that: The thickness of the outer insulating layer (901) is 2-3 mm.

7. The low-voltage lead of the offshore wind power transformer according to claim 1, characterized in that: The lengths of the parts extending from the upper ends of the four copper strands are the same, and the lengths of the parts extending from the lower ends are the same.

8. The low-voltage lead of the offshore wind power transformer according to claim 1, characterized in that: The axis and surrounding areas of the four copper strands are fixed with glass fiber rods (11).

9. A wiring method, characterized in that: include: Two low-voltage leads are used, and the wiring terminals of the two low-voltage leads are connected to the two sets of low-voltage bushings through the tail bushings (5) respectively; the exposed copper strands of the two low-voltage leads are connected correspondingly through the third wiring terminal (8).

10. The wiring method according to claim 9, characterized in that: The connection between the terminal block and the copper stranded wire is cold pressed or welded, and the terminal block and the low-voltage bushing are fixed with bolts.

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