Graphene high-conductivity copper coil set, graphene high-conductivity copper winding and processing method thereof, dry-type transformer

Abstract

The embodiment of the application discloses a graphene high-conductivity copper coil group, a graphene high-conductivity copper winding and a processing method thereof and a dry-type transformer. The graphene high-conductivity copper coil group comprises a first-end coil group, a middle coil group and a last-end coil group which are sequentially stacked. The outer diameter of the first-end coil group and the outer diameter of the last-end coil group are smaller than the outer diameter of the middle coil group, and the inner diameter of the first-end coil group and the inner diameter of the last-end coil group are larger than the inner diameter of the middle coil group. The outer diameter of the first-end coil group and the last-end coil group is smaller than the outer diameter of the middle coil group, and the inner diameter of the first-end coil group and the last-end coil group is larger than the inner diameter of the middle coil group, so that the insulation distance between the first-end coil and the last-end coil and the inner and outer walls of the insulator can be increased, the electric field intensity of the first-end coil and the last-end coil is reduced, and the probability of discharge breakdown is reduced. Since the insulation distance of the first-end coil group and the last-end coil group is increased, the filling space of the casting material is larger, so that the bubbles have more migration channels, and the partial discharge amount of the first-end coil group and the last-end coil group is reduced.

Description

Technical Field

[0001] This application relates to the field of dry-type transformer technology, specifically to a graphene high-conductivity copper coil group, a graphene high-conductivity copper winding and its processing method, and a dry-type transformer. Background Technology

[0002] Epoxy resin cast dry-type transformers are widely used in urban power grids, data centers, and rail transportation due to their flame-retardant, safe, and maintenance-free characteristics. The high-voltage coil is the core component of a dry-type transformer. Since the beginning and end of the high-voltage coil are the areas with the most concentrated electric field, according to the electric field distribution law, the electric field strength at the beginning and end of the coil relative to ground is much higher than that in the middle of the coil. In related technologies, the insulation distance between the beginning and end of the high-voltage coil and the outer wall of the epoxy resin is usually consistent with that in the middle of the coil. This makes the ends of the high-voltage coil in epoxy-cast dry-type transformers more susceptible to discharge breakdown due to insufficient insulation distance.

[0003] In response to the above situation, industry experience often suggests increasing the insulation distance by adding insulating end rings at the beginning and end of the coil or reducing the number of turns. However, changing the number of turns will increase the current density of the turns, and these methods fail to fully coordinate with the casting process, thus failing to fundamentally solve the problem of partial discharge and discharge breakdown risks in the high-voltage windings of dry-type transformers. Summary of the Invention

[0004] This application provides a graphene high-conductivity copper coil assembly, a graphene high-conductivity copper winding and its processing method, and a dry-type transformer, aiming to solve the problems of partial discharge and discharge breakdown in high-voltage windings.

[0005] This application provides a graphene high-conductivity copper coil assembly, comprising a first coil assembly, a middle coil assembly, and an end coil assembly stacked sequentially. The outer diameters of the first coil assembly and the end coil assembly are both smaller than the outer diameter of the middle coil assembly, and the inner diameters of the first coil assembly and the end coil assembly are both larger than the inner diameter of the middle coil assembly.

[0006] Optionally, in some embodiments of this application, the difference between the outer diameter of the first coil group and the outer diameter of the middle coil group is 3mm to 5mm; and / or The difference between the inner diameter of the first coil group and the inner diameter of the middle coil group is 3mm~5mm; and / or The difference between the outer diameter of the end coil group and the outer diameter of the middle coil group is 3mm to 5mm; and / or The difference between the inner diameter of the end coil group and the inner diameter of the middle coil group is 3mm to 5mm.

[0007] Optionally, in some embodiments of this application, the first coil group, the middle coil group, and the last coil group are formed by winding wires, and the bending radius of the wires of the first coil group and the last coil group is greater than the bending radius of the wires of the middle coil group.

[0008] Optionally, in some embodiments of this application, the bending radius of the conductor of the first-end coil group is greater than or equal to 5 times the width of the conductor of the first-end coil group; and / or The bending radius of the conductor in the end coil group is greater than or equal to five times the width of the conductor in the end coil group; and / or The bending radius of the conductor in the middle coil group is 2.5 to 3 times the width of the conductor in the middle coil group.

[0009] Optionally, in some embodiments of this application, the first coil group, the middle coil group, and the last coil group each include multiple coil layers, and each coil layer includes multiple coils from the inside out; Wherein, the gap between the coils in the coil layer of the first coil group is greater than the gap between the coils in the coil layer of the middle coil group; and / or The gap between the coils in the coil layers of the end coil group is greater than the gap between the coils in the coil layers of the middle coil group.

[0010] Optionally, in some embodiments of this application, the gap between the coils of the coil layer in the first-end coil group is 0.08mm to 0.15mm; and / or The gap between the coils in the coil layers of the end coil group is 0.08mm~0.15mm; and / or The gap between the coils in the coil layer of the middle coil group is 0.02mm~0.04mm.

[0011] Optionally, in some embodiments of this application, the first coil group includes a plurality of first coil layers stacked from the inside out. Along the axial direction away from the first coil group, the outer diameter of the first coil layer closer to the axial direction of the first coil group is larger than the outer diameter of the first coil layer farther from the axial direction of the first coil group; and / or The end coil group includes multiple second coil layers stacked from the inside out. Along the axial direction of the end coil group, the outer diameter of the second coil layer on the side closer to the axial direction of the end coil group is larger than the outer diameter of the second coil layer on the side farther from the axial direction of the end coil group.

[0012] Optionally, in some embodiments of this application, the first-end coil group includes a plurality of first coil layers stacked from the inside out, and a first insulating layer is provided between adjacent first coil layers and / or on one radial side of the plurality of first coil layers; and / or The end coil group includes multiple second coil layers stacked from the inside out, and a second insulating layer is provided between adjacent second coil layers and / or on one radial side of multiple second coil layers.

[0013] Optionally, in some embodiments of this application, the thickness of the first insulating layer is 0.35 mm to 0.4 mm; and / or The thickness of the second insulating layer is 0.35mm~0.4mm.

[0014] Accordingly, this application also provides a graphene high-conductivity copper winding, including the above-mentioned graphene high-conductivity copper coil assembly and an insulator covering the graphene high-conductivity copper coil assembly.

[0015] Optionally, in some embodiments of this application, the insulator includes an inner insulator and an outer insulator disposed radially along the graphene high-conductivity copper coil assembly, the inner insulator and the outer insulator being chemically bonded.

[0016] Optionally, in some embodiments of this application, an air passage is provided through the insulator.

[0017] Accordingly, this application also provides a method for processing graphene high-conductivity copper windings, including: The wire is wound into a coil to obtain a coil assembly; A first casting material is injected into the inner side of the coil assembly to carry out a first gel reaction, causing the first casting material to form a gel state. Then, a second casting material is injected into the outer side of the coil assembly to carry out a second gel reaction, forming an insulator covering the coil assembly, thus obtaining a graphene high-conductivity copper winding.

[0018] Optionally, in some embodiments of this application, the viscosity of the first castable is lower than the viscosity of the second castable; and / or The mass ratio of the first castable to the second castable is (0.6~1):1.

[0019] Optionally, in some embodiments of this application, the first casting material includes a first epoxy resin, the first epoxy resin having a viscosity of 800 mPa·s to 1200 mPa·s at 25°C. The first casting material includes a second epoxy resin, the second epoxy resin having a viscosity of 4000 mPa·s to 6000 mPa·s at 25°C.

[0020] Optionally, in some embodiments of this application, before injecting the first casting material into the inner side of the coil assembly, the method further includes: applying a coupling agent to the surface of the coil assembly; and / or After the first casting material is injected, the process also includes: subjecting the system to first electromagnetic oscillation and / or ultrasonic treatment; and / or During the injection of the second castable, the system is subjected to a second electromagnetic oscillation and / or ultrasonic treatment; and / or After the second casting material is injected, the process also includes: letting the system stand in a vacuum environment for 25 to 35 minutes.

[0021] Optionally, in some embodiments of this application, the coil group includes a first-end coil group, a middle coil group, and an end coil group stacked sequentially. During the process of winding the wire into a coil, the winding tension of the wire in the first-end coil group is 15% to 20% of the winding tension of the wire in the middle coil group; and / or The first electromagnetic oscillation is performed in an environment with a vacuum level of less than or equal to 30 Pa, the electromagnetic frequency of the first electromagnetic oscillation is 20 Hz to 50 Hz, and the duration of the first electromagnetic oscillation is 20 min to 40 min; and / or The injection rate of the first castable is 1.5 kg / min to 2 kg / min, the first castable is injected from bottom to top, and the first castable is injected under a vacuum of less than or equal to 30 Pa; and / or The first gelation reaction is carried out under a vacuum of 30 Pa or less, and includes: heating to 88°C to 92°C at a heating rate of 15°C / h and holding at that temperature for 2 to 3 hours; and / or The Shore hardness A of the gel formed by the first gelation reaction is 20-30; and / or The injection rate of the second refractory is 2.0 kg / min to 3.0 kg / min, and the second refractory is injected from bottom to top. During the injection of the second refractory, the top pressure of the coil assembly is 0.1 MPa to 0.3 MPa; and / or The electromagnetic frequency of the second electromagnetic oscillation is 30Hz~60Hz, and the second electromagnetic oscillation continues for 15min~25min after the second castable is injected; and / or The second gelation reaction includes: heating to 105℃~115℃ at a heating rate of 8℃ / h~12℃ / h and holding at that temperature for 3.5h~4.5h, then heating to 125℃~135℃ at a heating rate of 13℃ / h~17℃ / h and holding at that temperature for 5.5h~6.5h.

[0022] In addition, this application also provides a dry-type transformer, including the above-mentioned graphene high-conductivity copper winding, or the graphene high-conductivity copper winding processed by the above-mentioned processing method.

[0023] This application increases the insulation distance between the first and last coils and the inner wall of the insulator by making the outer diameter of the first and last coil groups smaller than that of the middle coil group, and the inner diameter of the first and last coil groups larger than that of the middle coil group. This reduces the electric field strength at the first and last coils, thereby reducing the probability of discharge breakdown. Due to the increased insulation distance between the first and last coil groups, the filling space of the castable is larger when the castable is injected, providing more migration channels for air bubbles, which in turn reduces the partial discharge of the first and last coil groups. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of a coil assembly provided in an exemplary embodiment of this application.

[0025] Explanation of reference numerals in the attached drawings: 1-First coil group; 11-First coil layer; 2-Middle coil group; 3-End coil group; 31-Second coil layer; 4-First insulation layer; 5-Second insulation layer; 6-Winding mold. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] The high-voltage coil is the core component of a dry-type transformer, and its casting quality directly determines the partial discharge, insulation life, and operational reliability of the transformer. The casting process for high-voltage coils mainly employs two methods: integral vacuum casting or segmented casting.

[0028] Vacuum casting involves placing the finished high-voltage coil blank into a vacuum casting tank and injecting an epoxy resin mixture in one go. While this process is simple, the complex interlayer structure of the windings makes it easy for air bubbles to form at corners and air passage junctions during resin penetration. After curing, these air bubbles can create voids or micro-cracks, becoming sources of partial discharge. In recent years, partial discharge exceeding standards in dry-type transformers has accounted for 15% to 20% of cases solely due to air bubbles during casting.

[0029] Segmented casting involves first casting the inner winding and then casting the outer layer after it has fully cured. While this process reduces the amount of material poured at one time and the amount of air bubbles generated to some extent, the clearly defined time intervals during casting result in a physical bond between the cured epoxy resin and the newly cast material at the interlayer interface. During the heating process of dry-type transformer operation, the bonding strength at the interface is low, making it highly susceptible to delamination and cracking between the intermediate layers, which can then lead to surface discharge breakdown.

[0030] This application provides a graphene high-conductivity copper coil assembly, a graphene high-conductivity copper winding and its processing method, and a dry-type transformer. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in a range format; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the counted range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is specified in this document, it means that any referenced number (fraction or integer) within the range is included.

[0031] Please see Figure 1 This application provides a graphene high-conductivity copper coil assembly, comprising a first coil assembly 1, a middle coil assembly 2, and a last coil assembly 3 stacked sequentially. The outer diameters of the first coil assembly 1 and the last coil assembly 3 are both smaller than the outer diameter of the middle coil assembly 2, and the inner diameters of the first coil assembly 1 and the last coil assembly 3 are both larger than the inner diameter of the middle coil assembly 2.

[0032] In this application, by making the outer diameter of the first coil group 1 and the outer diameter of the last coil group 3 smaller than the outer diameter of the middle coil group 2, and the inner diameter of the first coil group 1 and the inner diameter of the last coil group 3 larger than the inner diameter of the middle coil group 2, the insulation distance between the first and last coils and the inner and outer walls of the insulator can be increased, thereby reducing the electric field strength at the first and last ends, and thus reducing the probability of discharge breakdown. Since the insulation distance between the first coil group 1 and the last coil group 3 is increased, the filling space of the casting material is larger when the casting material is injected into the first coil group 1 and the last coil group 3, which makes the air bubbles have more migration channels, thereby reducing the partial discharge of the first coil group 1 and the last coil group 3.

[0033] It is understood that the first coil group 1, the middle coil group 2, and the last coil group 3 may include multiple coil layers stacked from the inside out. The first coil group 1, the middle coil group 2, and the last coil group 3 may each include multiple coil groups.

[0034] Optionally, in some embodiments of this application, the difference between the outer diameter of the first coil group 1 and the outer diameter of the middle coil group 2 is 3mm to 5mm, for example, 3.0mm, 3.3mm, 3.5mm, 3.7mm, 4.0mm, 4.3mm, 4.5mm, 4.7mm, 5.0mm, etc. This increases the insulation distance between the first coil group 1 and the outer wall of the insulator, allowing for a larger filling space for the casting material in the first coil group 1 during injection. This provides more migration channels for air bubbles, thereby reducing the partial discharge of the first coil group 1.

[0035] Optionally, in some embodiments of this application, the difference between the inner diameter of the first coil group 1 and the inner diameter of the middle coil group 2 is 3mm to 5mm, for example, it can be 3.0mm, 3.3mm, 3.5mm, 3.7mm, 4.0mm, 4.3mm, 4.5mm, 4.7mm, 5.0mm, etc. This increases the insulation distance between the first coil group 1 and the inner wall of the insulator, allowing for a larger filling space for the castable refractory in the first coil group 1 during injection, thus providing more migration channels for air bubbles and reducing the partial discharge of the first coil group 1.

[0036] As an example, the middle coil group 2 is cylindrical.

[0037] Optionally, in some embodiments of this application, the difference between the outer diameter of the end coil group 3 and the outer diameter of the middle coil group 2 is 3mm to 5mm, for example, 3.0mm, 3.3mm, 3.5mm, 3.7mm, 4.0mm, 4.3mm, 4.5mm, 4.7mm, 5.0mm, etc. This increases the insulation distance between the end coil group 3 and the outer wall of the insulator, allowing for a larger filling space for the casting material in the end coil group 3 during injection. This provides more migration channels for air bubbles, thereby reducing the partial discharge of the end coil group 3.

[0038] Optionally, in some embodiments of this application, the difference between the inner diameter of the end coil group 3 and the inner diameter of the middle coil group 2 is 3mm to 5mm, for example, 3.0mm, 3.3mm, 3.5mm, 3.7mm, 4.0mm, 4.3mm, 4.5mm, 4.7mm, 5.0mm, etc. This increases the insulation distance between the end coil group 3 and the inner wall of the insulator, resulting in a larger filling space for the castable material in the end coil group 3 during injection. This provides more migration channels for air bubbles and reduces dead zones where air bubbles may accumulate. This facilitates the directional migration and discharge of air bubbles accumulated in the end coil group 3, thereby reducing the partial discharge of the end coil group 3.

[0039] Optionally, in some embodiments of this application, the first coil group 1, the middle coil group 2, and the last coil group 3 are formed by winding wires, and the bending radius of the wires of the first coil group 1 and the last coil group 3 is greater than the bending radius of the wires of the middle coil group 2.

[0040] It is understandable that by making the bending radius of the wires of the first coil group 1 and the last coil group 3 greater than that of the wires of the middle coil group 2, the wires of the first coil group 1 and the last coil group 3 can be in a loose state during the winding process. This allows the first coil group 1 to be in an outwardly expanding step shape, thereby reducing the dead angle of bubble retention. This facilitates the directional migration and discharge of bubbles accumulated in the first coil group 1 and the last coil group 3, thereby reducing the electric field strength at the first and last ends and reducing the partial discharge at the first and last ends.

[0041] Optionally, in some embodiments of this application, the bending radius of the conductor of the first coil group 1 is greater than or equal to 5 times the width of the conductor of the first coil group 1, for example, it can be 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 12 times, 14 times, 15 times, etc.

[0042] It is understandable that the bending radius refers to the bending rate between segments of the guide wire. If the bending radius is too small, the cross-sectional area of ​​the wire will change after bending, which may lead to a short circuit. If the bending radius is greater than or equal to 5 times the width of the wire, the first coil group 1 can be in a loose state during the winding process, which is conducive to the expulsion of air bubbles during the casting process.

[0043] As an example, when the conductor is round, its width is its diameter; when the conductor is flat, the length of its wide side is its width.

[0044] Optionally, in some embodiments of this application, the bending radius of the conductor of the end coil group 3 is greater than or equal to 5 times the width of the conductor of the end coil group 3, for example, it can be 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 12 times, 14 times, 15 times, etc.

[0045] It is understandable that the bending radius refers to the bending rate between segments of the guide wire. If the bending radius is too small, the cross-sectional area of ​​the wire will change after bending, which may lead to a short circuit. If the bending radius is greater than or equal to 5 times the width of the wire, the first coil group 1 can be in a loose state during the winding process, which is conducive to the expulsion of air bubbles during the casting process.

[0046] Optionally, in some embodiments of this application, the bending radius of the conductor of the middle coil group 2 is 2.5 to 3 times the width of the conductor of the middle coil group 2, for example, it can be 2.5 times, 2.6 times, 2.7 times, 2.8 times, 2.9 times, 3 times, etc.

[0047] Optionally, in some embodiments of this application, the first coil group 1, the middle coil group 2 and the last coil group 3 each include multiple coil layers from the inside out, and each coil layer includes multiple coils; Among them, the gap between the coils in the coil layer of the first coil group 1 is greater than the gap between the coils in the coil layer of the middle coil group 2.

[0048] Understandably, the larger gap between the coils in the first coil group 1 allows for a larger gap for filling and flowing of the casting material, facilitating the flow of the casting material into the narrow areas between the first bends and layers, reducing the closed gaps formed by tightly attached wires, and reducing voids generated during the casting process. At the same time, it is beneficial for air bubbles inside the gaps to rise and escape outwards, allowing the air bubbles to drift out of the coil along the gap channels formed by the loose wires, reducing the number of air bubbles trapped at the end.

[0049] Optionally, in some embodiments of this application, the gap between the coils of the coil layer in the end coil group 3 is greater than the gap between the coils of the coil layer in the middle coil group 2.

[0050] Understandably, the larger gap between the coils in the end coil group 3 allows for a larger gap for filling and flowing of the casting material, facilitating the flow of the casting material into the end bend and narrow interlayer area, reducing the closed dead gaps formed by the tightly attached wires, and reducing voids generated during the casting process. At the same time, it is beneficial for air bubbles inside the gaps to rise and escape outwards, allowing the air bubbles to float out of the coil along the gap channels formed by the loose wires, reducing the number of air bubbles trapped at the end.

[0051] Optionally, in some embodiments of this application, the gap between the coils of the coil layer of the first coil group 1 is 0.08mm to 0.15mm, for example, it can be 0.08mm, 0.09mm, 0.11mm, 0.12mm, 0.13mm, 0.14mm, 0.15mm, etc.

[0052] Optionally, in some embodiments of this application, the gap between the coils of the coil layer of the end coil group 3 is 0.08mm to 0.15mm, for example, it can be 0.08mm, 0.09mm, 0.11mm, 0.12mm, 0.13mm, 0.14mm, 0.15mm, etc.

[0053] Optionally, in some embodiments of this application, the gap between the coils of the coil layer in the middle coil group 2 is 0.02mm to 0.04mm, for example, it can be 0.020mm, 0.023mm, 0.025mm, 0.027mm, 0.030mm, 0.033mm, 0.035mm, 0.037mm, 0.040mm, etc.

[0054] Optionally, in some embodiments of this application, the first-end coil group 1 includes a plurality of first coil layers 11 stacked from the inside out. Along the axial direction away from the first-end coil group 1, the outer diameter of the first coil layer 11 on the side closer to the axial direction of the first-end coil group 1 is larger than the outer diameter of the first coil layer 11 on the side farther from the axial direction of the first-end coil group 1. In this way, the first-end coil group 1 has an outwardly expanding stepped shape, which can increase the insulation distance at the first end of the first-end coil group 1, reduce the electric field strength at the first end, and keep the wires of the first-end coil group 1 in a loose state during the winding process, which is conducive to the discharge of air bubbles.

[0055] As an example, the number of turns of the first coil layer 11 stacked from the inside out in the first coil group 1 can be 10 turns, 10 turns, 8 turns, 8 turns, 6 turns, and 6 turns in sequence, so that the first coil group 1 can present an outwardly expanding stepped shape.

[0056] Optionally, in some embodiments of this application, the end coil group 3 includes a plurality of second coil layers 31 stacked from the inside out. Along the axial direction of the end coil group 3, the outer diameter of the second coil layer 31 on the side closer to the axial direction of the end coil group 3 is larger than the outer diameter of the second coil layer 31 on the side farther from the axial direction of the end coil group 3. In this way, the end coil group 3 has an outwardly expanding stepped shape, which can increase the end insulation distance of the end coil group, thereby reducing the end electric field strength. This allows the wires of the end coil group 3 to be in a loose state during the winding process, which is conducive to the discharge of air bubbles.

[0057] As an example, the number of turns of the second coil layer 31 stacked from the inside out in the end coil group 3 can be 10 turns, 10 turns, 8 turns, 8 turns, 6 turns, and 6 turns in sequence, so that the end coil group 3 can present an outwardly expanding stepped shape.

[0058] As an example, the conductor is a film-coated graphene copper flat wire, that is, a graphene copper flat wire coated with an epoxy resin or polymer film. The epoxy resin or polymer film itself is gas-repellent, and graphene has properties such as high temperature resistance and dense surface. Compared with elemental metal conductors, film-coated graphene copper flat wire has high temperature resistance, dense surface, and high conductivity at room temperature. During repeated heating in the casting process, it is conducive to the expulsion of air bubbles and can more effectively reduce the accumulation of microbubbles on the surface of elemental materials, which is more in line with the processing technology of this application.

[0059] Optionally, in some embodiments of this application, a first insulating layer 4 is provided between adjacent first coil layers 11 and / or on one radial side of multiple first coil layers 11.

[0060] It is understandable that by adding an insulation layer to the first coil group 1, the creepage distance can be increased, the interlayer voltage breakdown strength of the first coil group 1 can be improved, and the insulation performance of the first coil group 1 can be enhanced, which can be applied to the end of a 35kV high voltage coil.

[0061] As an example, the first insulating layer 4 can be disposed where the outer diameter of the first coil group 1 changes relative to the outer diameter of the middle coil group 2. The first insulating layer 4 can be manually added to the first coil layers 11 of the first coil group 1 during the winding process of the first coil group 1.

[0062] As an example, the first insulating layer 4 can be a three-layer flexible composite insulating material DMD, the structure of which is a polyester fiber nonwoven fabric, a polyester film, and a polyester fiber nonwoven fabric bonded together with an adhesive. The first insulating layer 4 can also be an end ring formed of materials such as epoxy resin preimpregnated glass fiber cloth.

[0063] Optionally, in some embodiments of this application, the thickness of the first insulating layer 4 is 0.35mm to 0.4mm, for example, it can be 0.35mm, 0.36mm, 0.37mm, 0.38mm, 0.39mm, 0.40mm, etc.

[0064] Optionally, in some embodiments of this application, a second insulating layer 5 is provided between adjacent second coil layers 31 and / or on one radial side of multiple second coil layers 31.

[0065] It is understandable that by adding an insulation layer to the end coil group 3, the creepage distance can be increased, the interlayer voltage breakdown strength of the end coil group 3 can be improved, and the insulation performance of the end coil group 3 can be enhanced, which can be applied to the end of a 35kV high voltage coil.

[0066] As an example, the second insulating layer 5 can be disposed where the outer diameter of the end coil group 3 changes relative to the outer diameter of the middle coil group 2. The second insulating layer 5 can be manually added to the second coil layer 31 of the end coil group 3 during the winding process of the end coil group 3.

[0067] As an example, the second insulating layer 5 can be a three-layer flexible composite insulating material (DMD), the structure of which is a polyester fiber nonwoven fabric, a polyester film, and a polyester fiber nonwoven fabric bonded together with an adhesive. The second insulating layer 5 can also be an end ring formed of materials such as epoxy resin pre-impregnated glass fiber cloth.

[0068] Optionally, in some embodiments of this application, the thickness of the second insulating layer 5 is 0.35mm to 0.4mm, for example, it can be 0.35mm, 0.36mm, 0.37mm, 0.38mm, 0.39mm, 0.40mm, etc.

[0069] This application also provides a graphene high-conductivity copper winding, including the above-mentioned graphene high-conductivity copper coil group and an insulator covering the graphene high-conductivity copper coil group.

[0070] Optionally, in some embodiments of this application, the insulator includes an inner insulator and an outer insulator arranged radially along the graphene high-conductivity copper coil assembly, and the inner and outer insulators are chemically bonded. This eliminates the overall interlayer stress in the high-voltage coil casting, improves the bonding strength at the interface between the inner and outer insulators, reduces the probability of delamination cracking, and consequently lowers the probability of interface discharge breakdown.

[0071] As an example, the chemical bond between the inner insulator and the outer insulator is a covalent ester bond.

[0072] Optionally, in some embodiments of this application, an air passage is provided through the insulator. This allows air to circulate within the air passage in the insulator, thereby carrying away the heat generated during coil operation.

[0073] It is understandable that the air channel can be formed in the following way: before the coil is cast with the refractory, an air channel rod is placed inside the casting mold; after the refractory forms the insulator, the air channel rod is pulled out, thus forming an air channel within the insulator. As an example, the material of the air channel rod is polytetrafluoroethylene (PTFE). The air channel rod is oblong, making it easy to pull out when removing the winding mold 6, forming an exposed air channel.

[0074] Optionally, in some embodiments of this application, multiple air passages are distributed at equal intervals along the axial direction of the coil.

[0075] This application also provides a method for processing graphene high-conductivity copper windings, including: The wire is wound into a coil to obtain a coil assembly; A first casting material is injected into the inner side of the coil assembly to carry out a first gel reaction, causing the first casting material to form a gel state. Then, a second casting material is injected into the outer side of the coil assembly to carry out a second gel reaction, forming an insulator covering the coil assembly, thus obtaining a graphene high-conductivity copper winding.

[0076] Optionally, in some embodiments of this application, the viscosity of the first castable is lower than that of the second castable.

[0077] Understandably, by differentiating the viscosity gradient of the castable material and injecting it in stages, firstly, a low-viscosity first castable material is poured into the inner side of the coil, causing the winding coil group to partially solidify and form a semi-formed gel state. Then, a high-viscosity second castable material is poured into the outer side, achieving controlled layer-by-layer filling from the inside out, and realizing interlayer chemical bonding through the gel state transition. Injecting the low-viscosity first castable material first ensures that the complex gap between the first coil group 1 and the last coil group 3 is fully filled, thereby reducing the partial discharge of the first coil group 1 and the last coil group 3.

[0078] Understandably, the fluid properties of low-viscosity castable make it suitable for narrow, tortuous gaps. When combined with the pre-widened gaps in the coil winding structure at the beginning and end of the coil, it can reduce dead corners and thus improve the filling rate of the complex gaps in the beginning coil group 1 and the end coil group 3.

[0079] Optionally, in some embodiments of this application, the mass ratio of the first casting material to the second casting material is (0.6~1):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, etc. In this way, the insulator formed by the first casting material can fully cover the inner side of the coil assembly, and the external dimensions of the insulator can be controlled by the second casting material, thereby enhancing the insulation characteristics of the entire winding.

[0080] Optionally, in some embodiments of this application, the first casting material includes a first epoxy resin, the viscosity of which at 25°C is 800 mPa·s to 1200 mPa·s, for example, 800 mPa·s, 850 mPa·s, 900 mPa·s, 950 mPa·s, 1000 mPa·s, 1050 mPa·s, 1100 mPa·s, 1150 mPa·s, 1200 mPa·s, etc. Thus, the epoxy resin molecules at this viscosity are smaller and have stronger fluidity. Combined with the vacuum negative pressure environment, this allows for thorough encapsulation of the coil assembly, reducing the generation of microbubbles.

[0081] As an example, the first casting material is composed of 100 parts of bisphenol A epoxy resin (viscosity of 800 mPa·s to 1200 mPa·s at 25°C), 85 parts of methyl hexahydrophthalic anhydride curing agent, and 1.5 parts of trimerizing catalyst.

[0082] Optionally, in some embodiments of this application, the first casting material includes a second epoxy resin, the viscosity of which at 25°C is 4000 mPa·s to 6000 mPa·s, for example, 4000 mPa·s, 4200 mPa·s, 4500 mPa·s, 4700 mPa·s, 5000 mPa·s, 5200 mPa·s, 5500 mPa·s, 5700 mPa·s, 6000 mPa·s, etc. Thus, the higher viscosity of the second epoxy resin makes it less prone to interpenetration with the first epoxy resin, and the outer insulating layer formed by the second epoxy resin has better insulation and crack resistance. Simultaneously, the high-viscosity epoxy resin system is less prone to sagging after molding, and the outer circle and end face contours of the cured winding are regular, less prone to unevenness and flow marks caused by resin flow.

[0083] As an example, the second casting material is composed of 100 parts of bisphenol A epoxy resin (viscosity of 4000 mPa·s to 6000 mPa·s at 25°C), 80 parts of methyl hexahydrophthalic anhydride curing agent, 35 parts of silica powder filler, and 1.2 parts of trimerizing catalyst.

[0084] It is understandable that the elastic gel formed by the low-viscosity epoxy resin in the first casting material after heating will retain a large number of unreacted hydroxyl and epoxy group active sites. When the second casting material is injected, the liquid second casting material will wet the inner gel, achieving close molecular-level contact. During the second gel reaction, the active functional groups remaining on the surface of the inner gel will undergo esterification and ring-opening reactions with the epoxy and acid anhydride components in the second casting material, thereby generating covalent ester bonds at the interface between the inner and outer layers, achieving chemical bonding between the inner and outer insulators.

[0085] Optionally, in some embodiments of this application, the coil group includes a first coil group 1, a middle coil group 2, and a last coil group 3 stacked sequentially. During the process of winding the wire into a coil, the winding tension of the wire in the first coil group 1 is 15% to 20% of the winding tension of the wire in the middle coil group 2, for example, 15%, 16%, 17%, 18%, 19%, 20%, etc. This allows the wire arrangement of the first coil group 1 to be looser.

[0086] Optionally, in some embodiments of this application, the winding tension of the conductors of the end coil group 3 is 15% to 20% of the winding tension of the conductors of the middle coil group 2, for example, 15%, 16%, 17%, 18%, 19%, 20%, etc. In this way, the conductors of the end coil group 3 can be arranged more loosely.

[0087] Optionally, in some embodiments of this application, before injecting the first casting material into the inner side of the coil assembly, the process further includes drying the coil assembly. This removes moisture and humidity absorbed by the wires during the winding process.

[0088] Optionally, in some embodiments of this application, the drying temperature is 115℃~125℃, for example, 115℃, 117℃, 118℃, 120℃, 122℃, 123℃, 125℃, etc., and the drying time is 4h~6h, for example, 4.0h, 4.3h, 4.7h, 5.0h, 5.3h, 5.7h, 6.0h, etc.

[0089] As an example, after drying, the coil assembly is allowed to cool naturally to 55°C~65°C before being removed from the oven.

[0090] Optionally, in some embodiments of this application, before injecting the first casting material into the inner side of the coil assembly, a coupling agent is further disposed on the surface of the coil assembly. This can enhance the interfacial bonding force between the coil assembly and the casting material.

[0091] As an example, the coupling agent can be the silane coupling agent KH-550.

[0092] Optionally, in some embodiments of this application, before injecting the first casting material into the casting mold, the coil assembly is further subjected to a heat treatment. This ensures that the air inside the coil assembly is fully expelled.

[0093] As an example, the heat treatment can be carried out at 70°C for 1 hour, and the heat treatment can be carried out in an environment with a vacuum degree of <20Pa.

[0094] Optionally, in some embodiments of this application, the injection rate of the first casting material is 1.5 kg / min to 2 kg / min, for example, it can be 1.5 kg / min, 1.6 kg / min, 1.7 kg / min, 1.8 kg / min, 1.9 kg / min, 2 kg / min, etc. The first casting material is injected from bottom to top, and the first casting material is injected in an environment with a vacuum degree of less than or equal to 30 Pa, for example, it can be 30 Pa, 27 Pa, 25 Pa, 23 Pa, 20 Pa, 17 Pa, 15 Pa, 13 Pa, 10 Pa, etc. In this way, the first casting material can fully penetrate into the gaps between the inner layers of the coil (including between conductors, between layers, at the beginning and end bends, around the air passages, etc.).

[0095] Understandably, the casting process and pre-casting stages are conducted in a vacuum environment, and the first batch of casting material, injected from bottom to top, slowly rises axially between the coil assemblies. This vacuum environment reduces air pockets between the coil assemblies, thereby increasing the coil fill factor.

[0096] Optionally, in some embodiments of this application, after the first castable is injected, the process further includes subjecting the system to first electromagnetic oscillation and / or ultrasonic treatment. This helps to remove air bubbles generated during the injection process of the first castable.

[0097] It is understandable that eddy currents are induced in the conductor in an alternating magnetic field. The interaction between the eddy currents and the magnetic field generates a Lorentz force. As a non-conductive material, the bubble experiences a different force than the conductive substrate in the electromagnetic field, resulting in relative motion. Under the action of buoyancy, the bubble migrates upward and is discharged from the casting mold, especially the bubbles gathered in the first coil group 1 and the last coil group 3, thereby increasing the coil filling rate. The ultrasonic cavitation effect can cause the bubbles to break and migrate, thus causing them to migrate upward and be discharged from the casting mold, thereby reducing the partial discharge of the first coil group 1 and the last coil group 3. By using electromagnetic oscillation, ultrasonic debubbling, and structural improvements to the first coil group 1 and the last coil group 3 in synergy, the efficiency and effect of bubble discharge at the first and last ends can be improved.

[0098] Optionally, in some embodiments of this application, the first electromagnetic oscillation is performed in an environment with a vacuum degree of less than or equal to 30 Pa, such as 30 Pa, 27 Pa, 25 Pa, 23 Pa, 20 Pa, 17 Pa, 15 Pa, 13 Pa, 10 Pa, etc. The electromagnetic frequency of the first electromagnetic oscillation is 20 Hz to 50 Hz, such as 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz, 50 Hz, etc. The duration of the first electromagnetic oscillation is 20 min to 40 min, such as 20 min, 23 min, 27 min, 30 min, 33 min, 37 min, 40 min, etc.

[0099] Understandably, the combined effect of vacuum suction and buoyancy results in higher efficiency and better removal of air bubbles.

[0100] Optionally, in some embodiments of this application, the first gelation reaction is carried out in an environment with a vacuum degree of less than or equal to 30 Pa, such as 30 Pa, 27 Pa, 25 Pa, 23 Pa, 20 Pa, 17 Pa, 15 Pa, 13 Pa, 10 Pa, etc. The first gelation reaction includes: heating to 88°C~92°C at a heating rate of less than or equal to 15°C / h (such as 15°C / h, 13°C / h, 12°C / h, 10°C / h, 8°C / h, 6°C / h, 5°C / h, etc.), such as 88°C, 89°C, 90°C, 91°C, 92°C, etc., and holding at this temperature for 2h~3h, such as 2.0h, 2.2h, 2.3h, 2.5h, 2.7h, 2.8h, 3.0h, etc. In this way, the first casting material can undergo a gelation reaction to form a gel body. The vacuum environment can reduce the air in the gaps between the coil groups, thereby improving the coil filling rate.

[0101] Optionally, in some embodiments of this application, the Shore A hardness of the gel formed by the first gel reaction is 20 to 30, for example, it can be 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, etc.

[0102] Optionally, in some embodiments of this application, the injection speed of the second casting material is 2.0 kg / min to 3.0 kg / min, for example, it can be 2.0 kg / min, 2.2 kg / min, 2.3 kg / min, 2.5 kg / min, 2.7 kg / min, 2.8 kg / min, 3.0 kg / min, etc. The second casting material is injected from bottom to top. During the injection of the second casting material, the top pressure of the coil assembly is 0.1 MPa to 0.3 MPa, for example, it can be 0.10 MPa, 0.13 MPa, 0.17 MPa, 0.20 MPa, 0.23 MPa, 0.27 MPa, 0.30 MPa, etc.

[0103] Understandably, the vacuum environment at the bottom of the coil assembly and the positive pressure at the top allow the second casting material to fully bond with the gel-state inner gel and better fill the small areas in the coil assembly that are not completely wetted.

[0104] Optionally, in some embodiments of this application, the system is subjected to second electromagnetic oscillation and / or ultrasonic treatment during the injection of the second castable. This helps to remove air bubbles generated during the injection process of the second castable.

[0105] It is understandable that eddy currents are induced in the conductor in an alternating magnetic field. The interaction between the eddy currents and the magnetic field generates a Lorentz force. As a non-conductive material, the bubble experiences a different force than the conductive substrate in the electromagnetic field, resulting in relative motion. Under the action of buoyancy, the bubble migrates upward and is discharged from the casting mold, especially the bubbles gathered in the first coil group 1 and the last coil group 3, thereby increasing the coil filling rate. The ultrasonic cavitation effect can cause the bubbles to break and migrate, thus causing them to migrate upward and be discharged from the casting mold, thereby reducing the partial discharge of the first coil group 1 and the last coil group 3. By using electromagnetic oscillation, ultrasonic debubbling, and structural improvements to the first coil group 1 and the last coil group 3 in synergy, the efficiency and effect of bubble discharge at the first and last ends can be improved.

[0106] Optionally, in some embodiments of this application, the electromagnetic frequency of the second electromagnetic oscillation is 30Hz~60Hz, for example, it can be 30Hz, 35Hz, 40Hz, 45Hz, 50Hz, 55Hz, 60Hz, etc., and the second electromagnetic oscillation continues for 15min~25min after the second casting material is injected, for example, it can be 15min, 17min, 19min, 20min, 22min, 23min, 25min, etc.

[0107] Optionally, in some embodiments of this application, after the injection of the second casting material is completed, the process further includes: allowing the system to stand in a vacuum environment for 25 to 35 minutes, for example, 25 minutes, 27 minutes, 29 minutes, 30 minutes, 31 minutes, 33 minutes, 35 minutes, etc. This allows the second casting material to fully penetrate the small amount of incompletely wetted areas in the coil assembly, and the vacuum environment reduces the air in the gaps between the coil assemblies, thereby improving the coil filling rate.

[0108] Optionally, in some embodiments of this application, the second gelation reaction includes: heating to 105°C~115°C at a heating rate of 8°C / h~12°C / h (e.g., 8.0°C / h, 9°C / h, 10°C / h, 11°C / h, 12°C / h, etc.), for example, 105°C, 107°C, 108°C, 110°C, 112°C, 113°C, 115°C, etc., and holding at this temperature for 3.5h~4.5h, for example, 3.5h, 3.7h, 3.8h, 4.0h, 4.2h. The temperature is raised to 125℃~135℃ at a rate of 13℃ / h~17℃ / h (e.g., 13℃ / h, 14℃ / h, 15℃ / h, 16℃ / h, 17℃ / h, etc.), for example, 125℃, 127℃, 128℃, 130℃, 132℃, 133℃, 135℃, etc., and held at that temperature for 5.5h~6.5h (e.g., 5.5h, 5.7h, 5.8h, 6.0h, 6.2h, 6.3h, 6.5h, etc.).

[0109] Understandably, during the heat treatment process of raising the temperature to 110℃, the second casting material begins to gel, while the gel formed by the first casting material continues to cross-link. The inner and outer layers undergo simultaneous curing reactions. During the heat treatment process of raising the temperature to 130℃, the inner and outer gel layers simultaneously complete their final cross-linking, forming an overall chemical bond to eliminate interlayer interfaces. The segmented step heating allows the inner layer gel and the outer layer of newly cast material to complete their final curing simultaneously, eliminating the overall interlayer stress of the coil. At the same time, it ensures that the inner and outer layers of the first coil group 1 and the last coil group 3 are simultaneously and densely cured, thereby reducing the partial discharge of the first coil group 1 and the last coil group 3.

[0110] As an example, after the first gel reaction, the system is cooled to 60°C at a rate of 20°C / h, and after the pressure is restored, the casting mold and winding are removed.

[0111] This application also provides a dry-type transformer, including the above-described graphene high-conductivity copper winding.

[0112] Example 1 A graphene-based high-conductivity copper winding, the processing method of which includes: Graphene copper flat wire coated with epoxy resin film is wound into coil groups using a winding mold. Each coil group comprises a first coil group, a middle coil group, and a last coil group, stacked sequentially. Each of these groups includes multiple coil layers. During the winding of the first and last coil groups, a 0.38mm DMD insulating pad is inserted between adjacent coil layers. The winding tension of the first and last coil groups is 18% of the winding tension of the middle coil group. Along the direction away from the middle coil group, the outer diameter of the coils in the first and last coil groups is equal to the outer diameter of the coil in the middle coil group. The outer diameter of the coils in the first and last coil groups gradually decreases from the same as that in the middle coil group to a larger than that in the middle coil group. The average outer diameter of the first and last coil groups is 4mm smaller than that in the middle coil group. The inner diameter of the coils in the first and last coil groups is the same as that in the middle coil group, gradually increasing to a larger than that in the middle coil group. The average inner diameter of the first and last coil groups is 4mm larger than that in the middle coil group. The bending radius of the coils in the first and last coil groups is 5 times the width of the graphene copper flat wire coated with epoxy resin film. The bending radius of the coils in the middle coil group is 3 times the width of the graphene copper flat wire coated with epoxy resin film. After removing the winding mold, place the coil assembly in a high-temperature oven and dry it at an ambient temperature of 120℃ for 5 hours. After drying, allow it to cool naturally to 60℃ before removing it from the oven. Apply silane coupling agent KH-550 to the surface of the coil assembly, then assemble the coated coil assembly into the casting mold. Insert a polytetrafluoroethylene gas channel rod between the casting mold and the coil assembly along the circumference of the coil assembly. Place the casting mold containing the coil assembly into the vacuum casting tank, close the tank door, start the vacuum pump, evacuate the tank to a vacuum level of 10 Pa, and maintain this state for 30 minutes. Then, start the heating device and heat to 70°C and maintain for 1 hour. Next, inject the casting material (by mass, 100 parts of bisphenol A epoxy resin heated to 60°C (viscosity 1000 mPa·s at 25°C), cured with methylhexahydrophthalic anhydride) from the bottom of the casting mold to the inside of the coil assembly using a metering pump at a flow rate of 1.8 kg / min. The mixture of 85 parts of the reagent and 1.5 parts of 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30, trimerizing catalyst) was vacuumed for 3 hours to obtain the product. During the injection process, the vacuum degree inside the vessel was maintained at 10 Pa. After injection, the vacuum state inside the vessel was maintained for 30 minutes, and an electromagnetic oscillation platform was started to perform low-frequency oscillation at a frequency of 35 Hz. After the electromagnetic oscillation continued for 30 minutes, the electromagnetic oscillation system was turned off, and the vacuum state was maintained. The temperature was increased to 90℃ at a heating rate of 15℃ / h. After maintaining the temperature for 3 hours, a nitrogen positive pressure of 0.2 MPa was applied to the top of the casting mold. Simultaneously, casting material (by mass, prepared by mixing 100 parts of bisphenol A epoxy resin heated to 65℃ (viscosity 5000 mPa·s at 25℃), 80 parts of methyl hexahydrophthalic anhydride curing agent, 35 parts of silica powder filler, and 1.2 parts of trimerizing catalyst, and then vacuuming for 2 hours) was injected from the bottom of the mold to the outside of the coil assembly. During the injection process, the electromagnetic induction was restarted. The oscillation system uses electromagnetic vibration at a frequency of 45Hz to oscillate continuously until 20 minutes after injection. After injection, the vacuum state inside the tank is maintained for 30 minutes. Then, the temperature is increased to 110℃ at a heating rate of 10℃ / h and held for 4 hours. Next, the temperature is increased to 130℃ at a heating rate of 15℃ / h and held for 6 hours. Finally, the temperature is decreased to 60℃ at a cooling rate of 20℃ / h to restore the gas pressure inside the tank. The casting tank is then opened, the casting mold is removed, and the winding is demolded by pulling out the air channel rod.

[0113] Example 2 This embodiment is basically the same as Embodiment 1, except that the bending radius of the coils of the first coil group and the last coil group in this embodiment is 10 times the width of the graphene copper flat wire covered by epoxy resin film.

[0114] Example 3 This embodiment is basically the same as Embodiment 1, except that the bending radius of the coils of the first coil group and the last coil group in this embodiment is 15 times the width of the graphene copper flat wire covered with epoxy resin film.

[0115] Example 4 This embodiment is basically the same as embodiment 1, except that the 0.38mm DMD insulating pad is not set in this embodiment.

[0116] Example 5 This embodiment is basically the same as Embodiment 1, except that the winding tension of the first and last coil groups is the same as that of the middle coil group in this embodiment.

[0117] Example 6 This embodiment is basically the same as Embodiment 1, except that electromagnetic oscillation is not used in this embodiment.

[0118] Example 7 This embodiment is basically the same as Embodiment 1, except that the viscosity of the bisphenol A epoxy resin in the first injection of the casting material is 800 mPa·s.

[0119] Example 8 This embodiment is basically the same as Embodiment 1, except that the viscosity of the bisphenol A epoxy resin in the first injection of the casting material is 1200 mPa·s.

[0120] Example 9 This embodiment is basically the same as Embodiment 1, except that the viscosity of the bisphenol A epoxy resin in the second injection of the casting material is 4000 mPa·s.

[0121] Example 10 This embodiment is basically the same as Embodiment 1, except that the viscosity of the bisphenol A epoxy resin in the second injection of the casting material is 6000 mPa·s.

[0122] Comparative Example 1 This comparative example is basically the same as Example 1, except that the second injection of casting material is replaced with the first injection of casting material.

[0123] Comparative Example 2 This comparative example is basically the same as Example 1, except that the inner and outer diameters of the coils of the first and last coil groups are equal to those of the coils of the middle coil group.

[0124] Test example: The performance of the graphene high-conductivity copper windings obtained in the examples and comparative examples was tested, and the test results are shown in Table 1.

[0125] Maximum electric field strength test method: The electric field simulation calculation of the three-dimensional model of the coil is carried out using finite element electric field simulation software, and the maximum electric field strength at the bending position at the beginning and end of the coil is extracted.

[0126] Interlayer interface shear strength test method: Take an integral sample of inner and outer layers from the cast coil and conduct an interlayer shear test using a material testing machine to characterize the interlayer chemical bonding effect with shear strength.

[0127] Partial discharge quantity test method: According to GB / T 1094.11-2021 standard, the partial discharge quantity at the beginning and end of the coil is tested using a partial discharge detector under power frequency withstand voltage conditions.

[0128] Breakdown test method: The winding is tested by a power frequency withstand voltage boost test, and the sample is observed to see if discharge breakdown occurs. No breakdown means the withstand voltage test is passed, and breakdown failure means that the sample has experienced discharge breakdown.

[0129] Table 1. Test Data Table

[0130] As can be seen from Table 1: Compared with Examples 1, 2, and 3, Example 3 has the smallest maximum electric field strength and the smallest partial discharge at the beginning and end of the winding. It can be seen that by increasing the bending radius of the coils at the beginning and end of the winding, the wires of the coils at the beginning and end of the winding can be in a loose state during the winding process. The coils at the beginning can be made to have an outwardly expanding step shape, which can reduce the dead angle of bubble retention. This is conducive to the directional migration and discharge of bubbles accumulated in the coils at the beginning and end of the winding, thereby reducing the electric field strength and the partial discharge at the beginning and end of the winding.

[0131] Compared with Example 4, Example 1 has a smaller maximum electric field strength at the beginning and end of the winding, a smaller partial discharge at the beginning and end, and a larger interlayer shear strength. It can be seen that by adding DMD insulating pads to the beginning and end coil groups, the creepage distance can be increased, the interlayer voltage breakdown strength of the beginning and end coil groups can be improved, thereby reducing the electric field strength at the beginning and end, reducing the partial discharge at the beginning and end, and increasing the interlayer shear strength of the insulator.

[0132] Compared with Example 5, Example 1 has a smaller maximum electric field strength at the beginning and end of the winding, a smaller partial discharge at the beginning and end, and a larger interlayer shear strength. It can be seen that by making the winding tension of the beginning and end coil groups less than that of the middle coil group, the wire arrangement of the beginning and end coil groups can be looser, which is conducive to the migration of bubbles accumulated in the beginning and end coil groups, thereby reducing the electric field strength at the beginning and end, reducing the partial discharge at the beginning and end, and increasing the interlayer shear strength of the insulator.

[0133] Compared with Example 6, Example 1 has a smaller maximum electric field strength at the beginning and end of the winding, a smaller partial discharge at the beginning and end, and a larger interlayer shear strength. It can be seen that when injecting the casting material, the efficiency and effect of bubble removal at the beginning and end can be improved by using electromagnetic oscillation, thereby increasing the coil filling rate, reducing the electric field strength at the beginning and end, reducing the partial discharge at the beginning and end, and increasing the interlayer shear strength of the insulator.

[0134] Compared with Examples 1, 7, and 8, Example 7 has a smaller maximum electric field strength at the beginning and end of the winding, a smaller partial discharge at the beginning and end, and a larger interlayer shear strength. It can be seen that when the viscosity of the first epoxy resin of the first casting material is within 800 mPa·s to 1200 mPa·s at 25°C, the lower the viscosity of the first casting material, the more fully the complex gap between the beginning and end coil groups is filled, and the stronger the bond between the inner and outer insulators. This can reduce the electric field strength at the beginning and end, reduce the partial discharge at the beginning and end, and increase the interlayer shear strength of the insulator.

[0135] Compared with Examples 1, 9, and 10, Example 1 has the smallest maximum electric field strength at the beginning and end of the winding, the smallest partial discharge at the beginning and end, and the largest interlayer shear strength. It can be seen that by controlling the viscosity of the first epoxy resin of the first casting material, the bonding force between the inner and outer insulators can be improved, the insulation and crack resistance of the outer insulator can be improved, thereby reducing the electric field strength at the beginning and end, reducing the partial discharge at the beginning and end, and increasing the interlayer shear strength of the insulator.

[0136] Compared with Comparative Example 1, Examples 1-10 show that Comparative Example 1 has the largest maximum electric field strength at the beginning and end of the winding, the largest partial discharge at the beginning and end, and the smallest interlaminar shear strength. It can be seen that by injecting low-viscosity castable first and then high-viscosity castable, the insulation and crack resistance of the insulator can be improved, thereby reducing the electric field strength at the beginning and end, reducing the partial discharge at the beginning and end, and increasing the interlaminar shear strength and breakdown resistance of the insulator.

[0137] Compared with Comparative Example 2, Examples 1-10 show that Comparative Example 2 has the largest maximum electric field strength at the beginning and end of the winding, the largest partial discharge at the beginning and end, and the smallest interlayer shear strength. It can be seen that by making the outer diameter of the beginning and end coil group smaller than that of the middle coil group, and the inner diameter of the beginning and end coil group larger than that of the middle coil group, the insulation distance between the beginning and end coil and the outer wall of the insulator can be increased, which is conducive to the migration of bubbles. This can reduce the electric field strength at the beginning and end, reduce the partial discharge at the beginning and end, and increase the interlayer shear strength and breakdown resistance of the insulator.

[0138] The foregoing has provided a detailed description of a graphene high-conductivity copper coil assembly, a graphene high-conductivity copper winding and its processing method, and a dry-type transformer provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A graphene high-conductivity copper coil assembly, characterized in that, It includes a first coil group (1), a middle coil group (2) and an end coil group (3) stacked in sequence. The outer diameter of the first coil group (1) and the outer diameter of the end coil group (3) are both smaller than the outer diameter of the middle coil group (2), and the inner diameter of the first coil group (1) and the inner diameter of the end coil group (3) are both larger than the inner diameter of the middle coil group (2).

2. The graphene high-conductivity copper coil assembly according to claim 1, characterized in that, The difference between the outer diameter of the first coil group (1) and the outer diameter of the middle coil group (2) is 3mm to 5mm; and / or The difference between the inner diameter of the first coil group (1) and the inner diameter of the middle coil group (2) is 3mm to 5mm; and / or The difference between the outer diameter of the end coil group (3) and the outer diameter of the middle coil group (2) is 3mm to 5mm; and / or The difference between the inner diameter of the end coil group (3) and the inner diameter of the middle coil group (2) is 3mm to 5mm.

3. The graphene high-conductivity copper coil assembly according to claim 1, characterized in that, The first coil group (1), the middle coil group (2) and the last coil group (3) are formed by winding wires. The bending radius of the wires of the first coil group (1) and the last coil group (3) is greater than the bending radius of the wires of the middle coil group (2).

4. The graphene high-conductivity copper coil assembly according to claim 3, characterized in that, The bending radius of the conductor of the first-end coil group (1) is greater than or equal to 5 times the width of the conductor of the first-end coil group (1); and / or The bending radius of the conductor of the end coil group (3) is greater than or equal to 5 times the width of the conductor of the end coil group (3); and / or The bending radius of the conductor of the middle coil group (2) is 2.5 to 3 times the width of the conductor of the middle coil group (2).

5. The graphene high-conductivity copper coil assembly according to claim 1, characterized in that, The first coil group (1), the middle coil group (2) and the last coil group (3) each include multiple coil layers from the inside out, and each coil layer includes multiple coils; Wherein, the gap between the coils in the coil layer of the first coil group (1) is greater than the gap between the coils in the coil layer of the middle coil group (2); and / or The gap between the coils in the coil layer of the end coil group (3) is greater than the gap between the coils in the coil layer of the middle coil group (2).

6. The graphene high-conductivity copper coil assembly according to claim 5, characterized in that, The gap between the coils in the coil layer of the first coil group (1) is 0.08mm~0.15mm; and / or The gap between the coils in the coil layer of the end coil group (3) is 0.08mm~0.15mm; and / or The gap between the coils in the coil layer of the middle coil group (2) is 0.02mm~0.04mm.

7. The graphene high-conductivity copper coil assembly according to claim 1, characterized in that, The first coil group (1) includes a plurality of first coil layers (11) stacked from the inside out. Along the axial direction away from the first coil group (1), the outer diameter of the first coil layer (11) closer to the axial direction of the first coil group (1) is larger than the outer diameter of the first coil layer (11) farther from the axial direction of the first coil group (1); and / or The end coil group (3) includes a plurality of second coil layers (31) stacked from the inside out. Along the axial direction of the end coil group (3), the outer diameter of the second coil layer (31) closer to the axial direction of the end coil group (3) is larger than the outer diameter of the second coil layer (31) farther away from the axial direction of the end coil group (3).

8. The graphene high-conductivity copper coil assembly according to claim 1, characterized in that, The first coil group (1) includes multiple first coil layers (11) stacked from the inside out, and a first insulating layer (4) is provided between adjacent first coil layers (11) and / or on one radial side of multiple first coil layers (11); and / or The end coil group (3) includes a plurality of second coil layers (31) stacked from the inside out, and a second insulating layer (5) is provided between adjacent second coil layers (31) and / or on one radial side of the plurality of second coil layers (31).

9. The graphene high-conductivity copper coil assembly according to claim 8, characterized in that, The thickness of the first insulating layer (4) is 0.35 mm to 0.4 mm; and / or The thickness of the second insulating layer (5) is 0.35mm~0.4mm.

10. A graphene-based high-conductivity copper winding, characterized in that, Includes the graphene high-conductivity copper coil assembly as described in any one of claims 1-9 and the insulator covering the graphene high-conductivity copper coil assembly.

11. The graphene high-conductivity copper winding according to claim 10, characterized in that, The insulator includes an inner insulator and an outer insulator arranged radially along the graphene high-conductivity copper coil assembly, wherein the inner insulator and the outer insulator are chemically bonded.

12. The graphene high-conductivity copper winding according to claim 10, characterized in that, An air passage is provided through the insulator.

13. A method for processing graphene high-conductivity copper windings, characterized in that, include: The wire is wound into a coil to obtain a coil assembly; A first casting material is injected into the inner side of the coil assembly to carry out a first gel reaction, causing the first casting material to form a gel state. Then, a second casting material is injected into the outer side of the coil assembly to carry out a second gel reaction, forming an insulator covering the coil assembly, thus obtaining a graphene high-conductivity copper winding.

14. The processing method of the graphene high-conductivity copper winding according to claim 13, characterized in that, The viscosity of the first castable is lower than that of the second castable; and / or The mass ratio of the first castable to the second castable is (0.6~1):

1.

15. The processing method of the graphene high-conductivity copper winding according to claim 14, characterized in that, The first casting material includes a first epoxy resin, the first epoxy resin having a viscosity of 800 mPa·s to 1200 mPa·s at 25°C; The first casting material includes a second epoxy resin, the second epoxy resin having a viscosity of 4000 mPa·s to 6000 mPa·s at 25°C.

16. The processing method of the graphene high-conductivity copper winding according to claim 13, characterized in that, Before injecting the first casting material into the inner side of the coil assembly, the method further includes: applying a coupling agent to the surface of the coil assembly; and / or After the first castable is injected, the method further includes: subjecting the system to first electromagnetic oscillation and / or ultrasonic treatment; and / or During the injection process of the second castable, the system is subjected to second electromagnetic oscillation and / or ultrasonic treatment; and / or After the second casting material is injected, the process also includes: allowing the system to stand in a vacuum environment for 25 to 35 minutes.

17. The processing method of the graphene high-conductivity copper winding according to claim 16, characterized in that, The coil group includes a first coil group (1), a middle coil group (2), and a last coil group (3) stacked sequentially. During the process of winding the wire into a coil, the winding tension of the wire in the first coil group (1) is 15% to 20% of the winding tension of the wire in the middle coil group (2); and / or The first electromagnetic oscillation is performed in an environment with a vacuum level of less than or equal to 30 Pa, the electromagnetic frequency of the first electromagnetic oscillation is 20 Hz to 50 Hz, and the duration of the first electromagnetic oscillation is 20 min to 40 min; and / or The injection rate of the first castable is 1.5 kg / min to 2 kg / min. The first castable is injected from bottom to top. The first castable is injected in an environment with a vacuum degree of less than or equal to 30 Pa. and / or The first gelation reaction is carried out under a vacuum of 30 Pa or less, and includes: heating to 88°C to 92°C at a heating rate of 15°C / h and holding at that temperature for 2 to 3 hours; and / or The Shore A hardness of the gel formed by the first gel reaction is 20-30; and / or The injection rate of the second castable is 2.0 kg / min to 3.0 kg / min, and the second castable is injected from bottom to top. During the injection of the second castable, the top pressure of the coil assembly is 0.1 MPa to 0.3 MPa; and / or The electromagnetic frequency of the second electromagnetic oscillation is 30Hz~60Hz, and the second electromagnetic oscillation continues for 15min~25min after the second castable is injected; and / or The second gelation reaction includes: heating to 105℃~115℃ at a heating rate of 8℃ / h~12℃ / h and holding at that temperature for 3.5h~4.5h, then heating to 125℃~135℃ at a heating rate of 13℃ / h~17℃ / h and holding at that temperature for 5.5h~6.5h.

18. A dry-type transformer, characterized in that, This includes the graphene high-conductivity copper winding as described in any one of claims 10-12, or the graphene high-conductivity copper winding processed by the processing method described in any one of claims 13-17.

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