Epoxy resin winding for dry-type transformer and method for manufacturing the same

Abstract

This invention discloses an epoxy resin winding for dry-type transformers and its preparation method, belonging to the technical field of dry-type transformers. It aims to solve the problems of poor environmental adaptability, insufficient mechanical strength, low heat dissipation efficiency, and rapid insulation aging in open-type non-cast dry-type transformer windings. Its structure, from the outside to the inside, includes a high-voltage casting body, an insulating cylinder, and a low-voltage casting body arranged coaxially. The high-voltage casting body has oval-shaped longitudinal heat dissipation holes arranged radially along its long axis; the low-voltage casting body adopts a unitized stress dispersion structure, and annular heat dissipation channels with staggered support bars are provided between adjacent low-voltage epoxy resin rings. The preparation method includes steps such as vacuum preheating and degassing, pressure casting, and stepped curing. This epoxy resin winding can significantly improve the heat dissipation performance and mechanical strength of the winding, suppress partial discharge to an extremely low level, enhance the transformer's short-circuit withstand capability and environmental adaptability, and ensure the safe and reliable operation of the power system.

Description

Technical Field

[0001] This invention belongs to the field of dry-type transformer technology, specifically relating to an epoxy resin winding for a dry-type transformer and its preparation method. Background Technology

[0002] Epoxy resin, as an excellent insulating material, is widely used in the manufacture of dry-type transformers due to its flame-retardant, self-extinguishing, and non-toxic gas-producing properties during operation. These characteristics allow dry-type transformers to be directly installed in densely populated areas such as buildings, subways, and shopping malls without the need for dedicated oil tanks and explosion-proof facilities, significantly enhancing the safety of power facilities and improving the flexibility of spatial layout.

[0003] However, traditional open-type non-cast dry windings still exhibit several technical limitations in actual operation. First, their insulation structure is highly dependent on environmental conditions, easily corroded by air moisture and dust accumulation, leading to a significant decline in insulation performance as the environment deteriorates, thus increasing the probability of creepage and flashover. Second, these windings have relatively weak mechanical strength, often exhibiting insufficient short-circuit withstand capability when subjected to the enormous electrodynamic impact of power system short circuits, easily causing serious faults such as winding loosening, deformation, and even burnout. Furthermore, the heat dissipation mechanism of traditional windings mainly relies on natural convection, resulting in generally low heat dissipation efficiency and limiting the equipment's ability to operate under continuous overload. Due to limitations in existing insulation processing technology, the partial discharge of these windings is usually maintained at a high level, significantly accelerating the electro-aging process of the insulation material, not only shortening the equipment's service life but also leading to a substantial increase in the frequency of subsequent operation, maintenance, and power outage repairs.

[0004] Based on this, the present invention proposes an epoxy resin winding for dry-type transformers and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an epoxy resin winding for dry-type transformers and its preparation method, which solves the problems of poor environmental adaptability, insufficient mechanical strength, low heat dissipation efficiency, and rapid insulation aging in existing open-type non-cast dry-type transformer windings.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a first solution: an epoxy resin winding for a dry-type transformer, comprising, from the outside to the inside, a high-voltage casting body, an insulating cylinder and a low-voltage casting body; The high-pressure casting body is cast and formed on the outside of the high-voltage coil, including a high-voltage epoxy resin winding. Several axially penetrating vertical holes are evenly distributed in the high-voltage epoxy resin winding along the circumferential direction. The cross-section of the vertical holes is long ellipse or waist-shaped, and the long axis of the vertical holes is arranged along the radial direction of the high-voltage epoxy resin winding. The insulating cylinder is concentrically positioned between the high-pressure casting body and the low-pressure casting body; The low-pressure casting body is cast and formed on the outside of the low-pressure coil. It includes multiple interconnected and integrally formed low-pressure epoxy resin rings. Air channels are reserved between two adjacent layers of low-pressure epoxy resin rings. Several air channel support strips are arranged alternately along the circumferential direction in the air channels.

[0007] In a preferred embodiment, the high-voltage casting body further includes a high-voltage outer insulation layer located outside the high-voltage epoxy resin winding and a high-voltage inner insulation layer located inside the high-voltage epoxy resin winding; and the high-voltage outer insulation layer, the high-voltage epoxy resin winding and the high-voltage inner insulation layer are integrally formed through the same vacuum casting cycle.

[0008] In a preferred embodiment, an array of turbulence-inducing elements is formed on the inner surface of the vertical hole, and the array of turbulence-inducing elements is arranged in a spiral ascending manner along the axial direction of the vertical hole.

[0009] In a preferred embodiment, the airway support strip has a hollow structure, and a support rib is provided inside the airway support strip and connected to the side wall of the airway support strip. The internal chamber of the airway support strip is divided into multiple buffer chambers by the support rib. The buffer chambers are connected to the airways on both sides respectively, and the support rib extends continuously in a sinusoidal wave shape along the length of the airway support strip.

[0010] In a preferred embodiment, the air duct support bars are staggered in the circumferential direction between two adjacent air duct layers; and inner insulation and outer insulation are integrally cast on the inner and outer sides of the low-pressure casting body, respectively. The inner insulation and outer insulation are respectively provided with connecting grooves for covering the connection parts of the low-pressure inner copper busbar and the low-pressure outer copper busbar; a high-pressure tap nut seat is integrally cast on the upper part of the high-pressure epoxy resin winding, and a high-pressure tap nut is encapsulated inside the high-pressure tap nut seat.

[0011] This invention provides a second solution: a method for preparing epoxy resin windings for dry-type transformers, comprising the following steps: Step 1: Coil winding and pre-placement arrangement; Step 2: Mold assembly. Place the wound coil into the casting mold for positioning and seal the mold. Step 3: Vacuum preheating treatment; Step 4: Vacuum pressure casting: Inject the epoxy resin mixture and apply dry nitrogen pressure of 0.3MPa to 0.5MPa for impregnation; Step 5: Step curing: Hold at 80℃ for 12 hours, raise the temperature to 100℃ and hold for 4 hours, then raise the temperature to 130℃ and hold for 6 hours, and finally let it cool naturally; the heating rate is 1.5℃ / min. Step Six: Perform demolding and post-processing.

[0012] In a preferred embodiment, in step one, when the coil is wound, if the coil structure is a double-layer cylindrical structure, the double-layer cylindrical coil winding method is used during the winding process; if the coil structure is a multi-layer cylindrical structure, the multi-layer cylindrical coil winding method is used during the winding process.

[0013] In a preferred embodiment, when using the double-layer cylindrical coil winding method, the wires are crossed and interchanged at halfway through the winding of one layer to balance the electromagnetic distribution, and the insulating paper between the layers is staggered by 10mm to 15mm; when using the multi-layer cylindrical coil winding method, a layer of insulating adhesive paper is first wound on the insulating cylinder before winding.

[0014] In a preferred embodiment, step three, vacuum preheating, includes: The assembled mold is placed into a vacuum casting tank, and the vacuum pump is started to reduce the pressure inside the tank to below 100Pa and raise the temperature to 80 to 100℃. Maintained in a high-temperature vacuum environment for 4 to 6 hours; Preheat the resin mixture and the curing agent mixture separately in an oven, then place them in their respective preheating tanks and maintain vacuum degassing for 2 to 4 hours, with the stirring speed controlled at 30 revolutions per minute to remove micro-bubbles from the mixture.

[0015] In a preferred embodiment, the temperature of the final mixing tank is raised to 65 to 70°C 2 hours before pouring, the pouring rate is controlled to be within 50 kg per hour for each pouring head, and vacuuming continues until the bubbles disappear after pouring.

[0016] Compared with the prior art, the present invention provides an epoxy resin winding for a dry-type transformer and its preparation method, which has the following beneficial effects: By setting oval vertical holes arranged radially along the long axis within the high-pressure casting body, combined with the air passages on the low-pressure side, a multi-dimensional three-dimensional heat dissipation network is constructed. This structure significantly increases the heat dissipation surface area, making the temperature distribution inside the winding more uniform and reducing the temperature of the hottest spot, thereby improving the transformer's continuous overload operation capability. At the same time, the oval hole structure also has a mechanical strengthening effect, improving the longitudinal stiffness of the winding.

[0017] The winding structure employs a three-layer sandwich integrated vacuum pressure casting process, which eliminates the physical interface between the insulation layer and the winding coil, thus avoiding partial discharge caused by the concentration of the interface electric field. At the same time, combined with vacuum degassing and high-pressure nitrogen impregnation processes, the amount of partial discharge inside the winding is suppressed to below 3pC, fundamentally delaying the electrical aging process of the insulation material.

[0018] The insulating cylinder acts as a central rigid support to withstand radial compressive force, while the staggered air channel support bars on the low-pressure side provide axial support. The support ribs inside the support bars act as dynamic load buffers. This combination of rigidity and flexibility can effectively resist the huge electro-mechanical stress generated during power system faults and short circuits, absorb the mechanical impact energy of the short circuit, and prevent the winding from undergoing cumulative deformation or brittle cracking.

[0019] The preparation method combines a stepped curing process with pressure impregnation technology, which scientifically balances the relationship between the heat release of resin curing and the heat dissipation of the mold. This solves the technical problem of internal stress cracks easily generated in large-volume epoxy resin castings, ensures the structural integrity of the finished winding throughout its entire life cycle, and reduces the frequency and cost of later operation and maintenance.

[0020] This solves the problems of poor environmental adaptability, insufficient mechanical strength, low heat dissipation efficiency, and rapid insulation aging in existing open-type non-cast dry-type transformer windings. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the dry-type transformer of the present invention.

[0022] Figure 2 This is a diagram showing the installation effect of the epoxy resin winding of the present invention.

[0023] Figure 3 This is an exploded view of the epoxy resin winding of the present invention.

[0024] Figure 4 This is a schematic diagram of the epoxy resin winding structure of the present invention.

[0025] Figure 5 This is a top view of the epoxy resin winding of the present invention.

[0026] Figure 6 This is a schematic diagram of the structure of the low-pressure casting body of the present invention.

[0027] Figure 7 This is a cross-sectional view of the vertical hole in this invention.

[0028] Figure 8 This is a cross-sectional view of the airway of the present invention.

[0029] Figure 9 This is a flowchart illustrating the preparation process of the epoxy resin winding of this invention.

[0030] The components include: 1. High-voltage casting body; 2. Insulating cylinder; 3. Low-voltage casting body; 4. High-voltage epoxy resin winding; 5. High-voltage outer insulation layer; 6. High-voltage inner insulation layer; 7. High-voltage tap nut seat; 8. High-voltage tap nut; 9. Inner insulation; 10. Outer insulation; 11. Air passage; 12. Air passage support bar; 13. Low-voltage epoxy resin ring; 14. Vertical hole; 15. Low-voltage outer copper busbar; 16. Low-voltage inner copper busbar; 17. Tinned copper busbar; 18. High-voltage lead wire; 19. Turbulence unit array; 20. Core rod; 21. Buffer cavity; 22. Support rib. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed following the word and its equivalents, but do not exclude other elements or objects.

[0032] As per the instruction manual Figure 1 To be continued Figure 9 As shown, in view of the problems existing in the prior art, embodiments of the present invention provide an epoxy resin winding, such as... Figure 1 As shown, the epoxy resin winding is installed on the outside of the transformer core lamination group in practical applications. Its structure, from the outside to the inside, includes a high-voltage casting body 1, an insulating cylinder 2, and a low-voltage casting body 3 arranged in concentric cylinders.

[0033] In one embodiment, such as Figure 1 and Figure 2 As shown, the high-voltage casting body 1 is cast and formed on the outside of the high-voltage coil to provide full-dimensional encapsulation and protection for the high-voltage coil, and is connected to the platinum-plated copper busbar 17 and high-voltage lead 18 in the transformer.

[0034] In one embodiment, such as Figure 1 and Figure 2 As shown, the insulating cylinder 2 is concentrically arranged between the high-pressure casting body 1 and the low-pressure casting body 3, and serves to provide insulation and protection.

[0035] In one embodiment, such as Figure 1 and Figure 2As shown, the low-voltage casting body 3 is concentrically arranged inside the insulating cylinder 2 and cast on the outside of the low-voltage coil to protect the low-voltage coil, and is connected to the low-voltage external copper busbar 15 and the low-voltage internal copper busbar 16 in the transformer.

[0036] The high-pressure casting body 1 and the low-pressure casting body 3 described in this invention are both integrally cast onto the outside of the high-pressure coil and the low-pressure coil by epoxy resin casting.

[0037] In one embodiment, such as Figure 2 As shown, the cross-section of the high-voltage casting body 1 presents a three-layer sandwich composite structure, which includes a high-voltage outer insulation layer 5, a high-voltage epoxy resin winding 4, and a high-voltage inner insulation layer 6 from the outside to the inside. The high-voltage epoxy resin winding 4 is cast and formed on the outside of the high-voltage coil, and the high-voltage outer insulation layer 5 and the high-voltage inner insulation layer 6 are used to protect the high-voltage epoxy resin winding 4.

[0038] In one embodiment, such as Figure 2 As shown, the thickness of the high-voltage outer insulation layer 5 and the high-voltage inner insulation layer 6 is determined based on the rated voltage level of the transformer and the lightning impulse withstand voltage requirements. The high volume resistivity of the epoxy resin material blocks the breakdown path of the high-voltage coil to ground and to the low-voltage side.

[0039] In one embodiment, in order to eliminate the physical interface between different insulation layers and prevent partial discharge caused by the accumulation of interface charge, the high-voltage epoxy resin winding 4, the high-voltage outer insulation layer 5, and the high-voltage inner insulation layer 6 are integrally formed in the same vacuum casting cycle.

[0040] In one embodiment, the thickness of the high-voltage outer insulation layer 5 and the high-voltage inner insulation layer 6 is between 3 mm and 5 mm. This thickness parameter has been selected after electric field strength verification to ensure that the maximum electric field strength on the winding surface is within acceptable limits under extreme conditions such as rated operating voltage, switching overvoltage, and lightning impulse voltage. E max The electric field strength is always kept below the air ionization breakdown field strength threshold, so that the electric field strength on the winding surface is always lower than the breakdown field strength of air, thereby preventing corona generation through physical barrier effect.

[0041] In one embodiment, such as Figure 3 As shown, to solve the heat dissipation problem caused by the fully enclosed structure, several vertical holes 14 are evenly distributed along the circumference inside the high-pressure epoxy resin winding 4 to provide support and heat dissipation. The vertical holes 14 are completely through the winding in the axial direction, forming a set of vertical air convection channels.

[0042] In this embodiment, the vertical holes 14, when the transformer operates under load causing the windings to heat up, cause the air inside the vertical holes 14 to expand due to heat, reducing its density. Under buoyancy, the air moves upwards, creating a negative pressure at the bottom of the vertical holes 14 and drawing in cool air. This continuous airflow removes the heat accumulated inside the windings through convective heat transfer, keeping the hottest spot temperature of the high-voltage winding within the heat resistance range of the insulation material. Furthermore, after curing, the slightly elastic support rings formed on the walls of the vertical holes 14 in the vertical direction effectively improve the axial compressive strength of the high-voltage epoxy resin winding 4.

[0043] Furthermore, this embodiment constructs a highly efficient internal circulation heat dissipation system through the vertical holes 14 and the air ducts 11. According to fluid mechanics principles, when the winding temperature rise reaches a set threshold, the airflow velocity within the vertical holes 14 increases significantly. This active convection heat dissipation mechanism allows the heat generated inside the windings to be rapidly conducted through the resin matrix to the hole wall surface and carried away by the airflow. This solution effectively controls the hottest temperature of the transformer under rated load, significantly enhancing the short-term overload capacity of the equipment and enabling it to adapt to operating conditions with drastic load fluctuations.

[0044] In one embodiment, such as Figure 3 As shown, the arrangement of the vertical holes 14 is based on the results of thermodynamic simulation optimization. The cross-section of the vertical holes 14 is preferably elongated ellipse or oval, with the major axis arranged radially along the winding. This geometric design maximizes the heat dissipation surface area without significantly reducing the effective cross-sectional area of ​​the coil. Simultaneously, after curing, the walls of the vertical holes 14 form a longitudinal rigid support surface resembling a biomimetic honeycomb structure. These support structures significantly enhance the axial compressive modulus of the high-voltage casting 1 in the vertical direction, effectively preventing creep deformation of the winding under long-term thermal stress cycling or mechanical tensile loads from the high-voltage leads.

[0045] In one embodiment, such as Figure 7 As shown, a turbulence unit array 19 consisting of several micro-dimples or micro-protrusions is formed on the inner surface of the vertical hole 14 by a mandrel 20. The turbulence unit array 19 is arranged in a spiral upward manner along the axial direction of the vertical hole 14, and the ratio of the radial depth or height of the turbulence unit array 19 to the length of the major axis of the vertical hole 14 is 1:50 to 1:150. This ratio balances the relationship between the turbulence effect and the airflow resistance.

[0046] In this embodiment, the heat generated by the windings is conducted to the wall of the vertical hole 14 when the transformer is running, thanks to the arrangement of the turbulence unit array 19. As the cold air enters from the bottom, it encounters the first-stage spirally arranged fish-scale protrusions during its ascent, causing axial deflection. Subsequently, it undergoes minor impacts with the wall surface, forming localized turbulence, which draws the hot air near the wall of the vertical hole 14 into the center of the hole, achieving efficient heat exchange.

[0047] In one embodiment, such as Figure 4 As shown, a high-voltage tap nut seat 7 is integrally cast in the upper region of the high-voltage epoxy resin winding 4. A high-voltage tap nut 8 is installed inside the high-voltage tap nut seat 7. The high-voltage tap nut 8 is electrically connected to the internal tap of the high-voltage winding through a pre-embedded conductive braided strip or copper foil.

[0048] In this embodiment, the high-voltage casting body 1 is tightly connected to the tinned copper busbar 17 and the high-voltage lead 18 after installation by using the high-voltage tap nut 8. Furthermore, by embedding the entire connection part inside the epoxy resin casting body, the high-potential tip exposed to the air is eliminated, thereby suppressing the generation of corona discharge at the source.

[0049] In addition, the high-pressure tap nut 8 is preferably made of chromium-zirconium-copper alloy (Cu-Cr-Zr), and a silver plating layer is provided on the surface of the high-pressure tap nut 8.

[0050] In one embodiment, such as Figure 1 , Figure 2 and Figure 3 As shown, the insulating cylinder 2 serves as an intermediate barrier connecting the high and low pressure sides. Both its upper and lower end faces are higher than the high pressure casting body 1 and the low pressure casting body 3, and its material is preferably a high-strength glass fiber reinforced epoxy resin matrix composite (GFRP).

[0051] In this embodiment, the insulating cylinder 2 acts as a crucial mechanical skeleton in the entire winding system, providing radial rigid support for the system. When a sudden short-circuit fault occurs on the transformer side, the instantaneous short-circuit current generates enormous electrodynamic force, which manifests as a huge radial expansion or compression tendency in the winding. With its high elastic modulus and high bending strength, the insulating cylinder 2 can effectively resist the radial displacement of the winding, ensuring that the winding can maintain geometric stability when subjected to short-circuit electrodynamic impact, thereby protecting the inter-turn insulation from physical damage.

[0052] In one embodiment, such as Figure 6As shown, the low-pressure casting body 3 is formed by multiple interconnected and integrally molded low-pressure epoxy resin rings 13, which are cast onto the outside of the low-pressure coil. These low-pressure epoxy resin rings 13 are arranged in multiple concentric layers in the radial direction, and annular gaps are reserved between adjacent low-pressure epoxy resin rings 13, thereby forming air channels 11 for heat dissipation.

[0053] In one embodiment, such as Figure 6 As shown, multiple airway support strips 12 are arranged alternately along the circumferential direction within the airway 11. The airway support strips 12 are staggered in the circumferential direction between adjacent airway layers 11, forming an interlaced support network. The airway support strips 12 are preferably prefabricated components made of heat-resistant insulating material, with one outer wall abutting against the outer wall of the inner resin ring and the other outer wall abutting against the inner wall of the outer resin ring.

[0054] This embodiment forms a heat dissipation system through the arrangement of air passage 11 and air passage support 12. The air passage support 12 not only maintains the geometry of air passage 11 by supporting it, but also transmits the force to the entire casting body when the low voltage winding is subjected to the radial expansion force of short-circuit electric force, and uses the high tensile strength of epoxy resin to offset the destructive force.

[0055] In one embodiment, such as Figure 8 As shown, in order to reduce the weight of the airway support strip 12 while ensuring the continuity of the airway 11, the airway support strip 12 is designed to be a hollow structure, and a support rib 22 is provided inside the airway support strip 12 and connected to the side wall of the airway support strip 12. The internal cavity of the airway support strip 12 is divided into multiple buffer chambers 21 by the support rib 22. The buffer chambers 21 are respectively connected to the airways 11 on both sides, and the support rib 22 extends continuously in a sinusoidal wave shape along the length of the airway support strip 12.

[0056] In this embodiment, when the transformer is subjected to instantaneous strong expansion caused by short-circuit current, the support rib 22 absorbs and converts electromagnetic vibration energy through the slight elastic deformation of its geometry, protecting the low-voltage epoxy resin ring 13 from brittle fracture.

[0057] In one embodiment, such as Figure 6As shown, the design width of the air passage 11 is between 8mm and 12mm, and its total cumulative width in the radial direction is preferably 1 / 10 to 1 / 5 of the total radial thickness of the low-pressure casting body 3. This proportional configuration not only ensures the smooth flow of the cooling medium in the passage and reduces flow resistance, but also forms a mechanical stress transmission chain with the air passage support strips 12. When the low-voltage winding is subjected to strong compression by short-circuit electric force, the radial stress is evenly distributed to the circumferential cross-section of the entire casting body through these staggered air passage support strips 12, effectively avoiding stress concentration effects and preventing cracks or brittle fractures of the resin layer due to local overload.

[0058] In one embodiment, such as Figure 6 As shown, the air duct support bars 12 are arranged in a staggered manner during installation, that is, the air duct support bars 12 in two adjacent layers of air ducts 11 are staggered by a certain angle in the circumferential direction. This staggered structure changes the transmission path of electromagnetic force, and evenly distributes the radial pressure during a short circuit to the entire circumference of the winding, thereby improving the deformation resistance of the low-voltage winding by avoiding stress concentration.

[0059] In one embodiment, such as Figure 6 As shown, an inner insulation 9 is integrally cast on the inner side of the low-pressure casting body 3. A connecting groove for embedding and installing the low-pressure inner copper busbar 16 is formed between the inner insulation 9 and the innermost low-pressure epoxy resin ring 13 through a mold.

[0060] In one embodiment, such as Figure 6 As shown, the number of layers of the low-pressure epoxy resin ring 13 is adjusted according to the voltage level and current capacity, typically ranging from 3 to 6 layers. The width of the air passage 11 between adjacent low-pressure epoxy resin rings 13 is maintained between 8 mm and 12 mm.

[0061] In one embodiment, such as Figure 6 As shown, an outer insulation 10 is integrally cast on the outside of the low-pressure casting body 3, and another connecting groove for installing the low-pressure external copper busbar 15 is formed between the outer insulation 10 and the outermost low-pressure epoxy resin ring 13.

[0062] In this embodiment, the low-voltage external copper busbar 15 and the low-voltage internal copper busbar 16 are welded or crimped to the low-voltage coils in their corresponding connection slots. Due to the presence of the inner insulation 9 and the outer insulation 10, these large-section copper busbar connection parts are completely covered in a resin layer with high dielectric strength, which greatly increases the creepage distance at the lead-out end, effectively preventing phase-to-phase flashover even in humid or dusty environments.

[0063] In one embodiment, such as Figure 6As shown, the edges of the inner insulation 9 and the outer insulation 10 preferably use a rounded corner transition structure to optimize the local electric field distribution and avoid electric field concentration.

[0064] In one embodiment, such as Figure 1 As shown, the epoxy resin substrates used in both the high-pressure casting body 1 and the low-pressure casting body 3 contain highly thermally conductive inorganic nanofillers that are uniformly dispersed.

[0065] In one embodiment, such as Figure 1 As shown, the nanofiller comprises nano-sized alumina (Al2O3) or aluminum nitride (AlN) powder modified with KH-560 silane coupling agent. These nanoparticles form a microscopic heat conduction network in the resin matrix through a mixing process. By introducing high thermal conductivity, the thermal resistance path for heat transfer from the inside of the winding conductors to the heat dissipation surface is shortened, effectively suppressing the hot-spot temperature inside the winding within the heat resistance rating of the insulation material (such as F or H class), thus enhancing the transformer's ability to withstand short-term overload operation.

[0066] In one embodiment, such as Figure 1 As shown, the rigid encapsulation structure of the high-voltage casting body 1 and the low-voltage casting body 3 provides robust short-circuit protection for the transformer. When a sudden short circuit occurs in the system, a significant magnetic force is generated between the winding conductors. The cured epoxy resin forms a rigid whole, firmly securing each turn of the conductor. The high-voltage outer insulation layer 5 and the high-voltage inner insulation layer 6 provide radial restraint, while the air duct support bar 12 provides stable radial support on the low-voltage side. This structural design ensures that the winding geometry remains unchanged when faced with extreme short-circuit current impacts, and the inter-turn insulation of the coils is not damaged by physical friction.

[0067] In actual operation, when the transformer is under load, the heat generated by the resistance loss of the coil wires is conducted through the highly thermally conductive resin matrix to the inner wall of the vertical hole 14 and the surface of the air passage 11. Because the vertical hole 14 has an oval design, its heat exchange area is effectively increased, allowing for rapid heat exchange with the air inside the hole. Simultaneously, the turbulence unit array 19 on the hole wall promotes spiral turbulence in the airflow, significantly improving the air's heat exchange efficiency. The heated air is discharged from the top of the winding through convection, while cool air continuously replenishes it from the bottom, forming a stable internal circulation for heat dissipation. On the low-pressure side, the air passage 11, in conjunction with the staggered air passage support bars 12, assists in heat dissipation by guiding airflow.

[0068] Meanwhile, in terms of short-circuit resistance, the windings generate a huge magnetic force under the condition of a sudden short circuit impact from the power grid. The integrated three-layer structure on the high-voltage side forms a rigid whole, converting the electrodynamic force into uniform internal stress in the resin matrix. Due to the reinforcing effect of the nanofillers in the resin, its tensile and shear strengths are significantly improved. On the low-voltage side, the radial expansion force is converted into multi-point distributed circumferential pressure through the staggered air channel support bars 12, while the support ribs 22 inside the air channel support bars 12 absorb the impact energy through slight deformation. The insulating cylinder 2, as the core support structure, ensures that the overall geometry of the winding does not become unstable and deformed, thereby protecting the inter-turn insulation from physical damage.

[0069] Furthermore, in humid, salt spray, or severely dust-polluted environments, the high-voltage tap joints and low-voltage copper busbar connections are encapsulated within an epoxy resin body, and the outer insulation layer provides a long creepage path, resulting in extremely strong anti-flashover capabilities for the windings. Partial discharge is suppressed to below 3 pC, significantly slowing down the electrical aging process of the insulation material. Through the synergistic effect of the above structure and process, this invention achieves a comprehensive improvement in the heat dissipation performance, mechanical strength, insulation life, and environmental adaptability of dry-type transformer windings, ensuring the safe and stable operation of the power system.

[0070] like Figure 9 As shown, embodiments of the present invention also provide a method for preparing epoxy resin windings. This method uses a vacuum pressure casting process to prepare the aforementioned high-pressure casting body 1 and low-pressure casting body 3. It includes: Step 1: Coil winding and pre-placement arrangement; Step 1.1: First, arrange the pre-placed items; When winding the high-voltage coil, core rods 20 made of easily demolded material are inserted at specific corner or radial positions between layers. The geometry of these core rods 20 determines the size of the subsequent vertical holes 14. When winding the low-voltage coil, annular baffles are used to isolate the air passage 11, air passage support strips 12 are placed between layers, and initial positioning is achieved with insulating tape. The buffer cavity 21 of the air passage support strip 12 is sealed with a core. At the same time, the high-voltage tap nut seat 7 and the low-voltage copper busbar with connecting terminals are pre-positioned at the corresponding design coordinates.

[0071] Step 1.2: Wind the high-voltage coil and the low-voltage coil; When winding the coil, high-voltage coils and low-voltage coils are wound separately according to the design drawings. The winding methods include double-layer cylindrical coil winding method and multi-layer cylindrical coil winding method.

[0072] When the winding body coil structure of the high-pressure casting body 1 and the low-pressure casting body 3 is a double-layer cylindrical coil, the double-layer cylindrical coil winding method is adopted. The operation process includes: pulling the wire out of the coil, and according to the winding direction and protrusion length specified in the drawing, using the method of winding from left to right or from right to left, using a curve cutter to complete the 90° right-angle bend of the wire; after bending the protrusion, removing the damaged insulation, adding four layers of crepe paper half-fold wrapping, and wrapping one layer of heat shrink tape; placing the insulated wire protrusion in the baffle slot of the winding mold, positioned on the center line of the baffle; when starting to wind, while winding, evenly placing heat shrink tape along the circumference under the coil, with one end of the heat shrink tape covering the end insulation; winding to a certain point... When the coil ends and the second turn begins, reinforce the insulation on the conductor and place a paper groove, then wrap it with a layer of heat shrink tape in half-overlap. When the conductor is wound to the middle of the first layer, tighten and press the heat shrink tape evenly. When the conductor is wound to the halfway point of the first layer, cross the conductors to balance the electromagnetic distribution. The insulating paper between the layers is staggered by 10 to 15 mm. When the coil is wound to the end, add a paper groove between the last turn and the exit point, wrap it with a layer of heat shrink tape in half-overlap, and tie the heat shrink tape at the end. The outermost layer of the coil is wrapped with a layer of heat shrink tape in half-overlap to enhance mechanical strength.

[0073] When the winding body coil structure is a multi-layer cylinder, a multi-layer cylindrical coil winding method is used. The operation process includes: adjusting the tensioning device to ensure that the conductor is not significantly stretched; before winding, wrap a layer of insulating adhesive paper on the insulating cylinder; when winding the conductor to the next layer, place multiple layers of cable paper as interlayer insulation, with a width slightly larger than the axial dimension of the coil; when winding to the point where there are air channel support strips 12 between layers, place them according to the dimensions and surround the outer layer with insulating cardboard; during the winding process, tighten the conductor, requiring each layer of wire turns to be fully wound and tightly packed, ensuring that the entire coil is firm and compact.

[0074] Step 2: Perform mold assembly; Step 2.1: Place the wound coil into the casting mold; Step 2.2: Ensure the correct position of the connecting grooves of the high-voltage tap nut seat 7, inner insulation 9, and outer insulation 10 by using the positioning pins of the mold; Step 2.3: Coat the inner wall of the mold with an organosilicon release agent to reduce the resistance to demolding after curing; Step 2.4: Before closing the mold, remove all foreign objects, surround with reinforcing insulation materials such as fiberglass mesh as required, and finally close the outer template and the top cover plate; Step 2.5: Tighten the four and center screws to ensure that all screws are tightened to a consistent degree; Step 2.6: Apply sealing adhesive to all seams, and seal areas prone to leakage with silicone sealant. After sealing, let it sit at room temperature for 1 to 2 hours, then place it in an oven for pre-drying.

[0075] Step 3: Vacuum preheating treatment; Step 3.1: Send the assembled mold into the vacuum casting tank, start the vacuum pump to reduce the pressure inside the tank to below 100Pa, and heat it to 80 to 100℃.

[0076] Step 3.2: Maintain the high temperature vacuum environment for 4 to 6 hours to completely remove moisture, air and volatile organic compounds from the coil fiber material using vacuum negative pressure, eliminating the risk of air bubbles or voids during the casting process.

[0077] Step 3.3: Simultaneously, preheat the resin mixture and the curing agent mixture in an oven, then place them in their respective preheating tanks and maintain vacuum degassing for 2 to 4 hours, with the stirring speed controlled at 30 revolutions per minute to ensure that the mixture is free of microbubbles.

[0078] In this process, after the modified nanofiller is added to the resin (to prepare a resin mixture), it is sheared at 3000-5000 rpm for 2 hours using a high-shear disperser, followed by vacuum membrane degassing to ensure that the filler is dispersed as single particles in the resin and does not agglomerate.

[0079] Step 4: Perform vacuum pressure casting; Step 4.1: Under the condition of maintaining vacuum, open the pouring valve and inject the epoxy resin mixture into the mold; the mixture contains nano-sized silica powder or alumina filler to improve the thermal conductivity of the resin. Step 4.2: Two hours before pouring, raise the temperature of the final mixture to 65 to 70°C to reduce its viscosity; Step 4.3: After injection, apply dry nitrogen pressure of 0.3MPa to 0.5MPa into the tank. Under the action of positive and negative pressure difference, the liquid resin is forcefully pressed into the extremely small gaps between the coil wires, achieving complete impregnation. During the pouring process, strictly control the rate, ensuring uniform flow distribution in each pouring pipe to guarantee a steady rise in the resin level. During pouring, place one of the 10 pouring pipes in an empty cylinder. Before pouring begins, perform 3 to 4 strokes as supplementary material. Simultaneously, the pouring rate should be: the pouring volume per pouring pipe should not exceed 1kg per stroke. For each pouring head, the maximum flow rate per hour should be controlled within 50kg, and the interval between each stroke should be as uniform as possible. After pouring, a vacuum must be applied for 15 minutes. If dense air bubbles remain at the pouring port, continue vacuuming until the bubbles essentially disappear. After pouring, allow the pouring system to cool down as quickly as possible and flush the pipes with a flushing agent to remove all remaining material droplets.

[0080] Step 5: Perform stepped curing; The mold is moved into the curing oven and cured according to the preset temperature curve. The curing process first holds the mold at 80°C for 12 hours. During this stage, the resin undergoes primary cross-linking, changing from a liquid state to a gel state and slowly releasing the polymerization shrinkage stress. Then, the temperature is raised to 100°C and held for 4 hours to promote further cross-linking reaction. Finally, the temperature is raised to 130°C and held for 6 hours for complete curing, so that the resin forms a highly stable three-dimensional network molecular structure, achieving the mechanical strength and insulation level required by the design.

[0081] The stepped heating rate is 1.5℃ / min. Excessive heating can cause a large temperature difference between the inside and outside of the winding, generating irreversible thermal stress; while excessively slow heating can lead to a long production cycle and may cause filler settling. The turbulence unit array 19 is formed by removing the mandrel 20 in a semi-cured state.

[0082] Step Six: Perform demolding and post-processing; After the mold has cooled to room temperature, it is demolded. Finally, the winding surface is trimmed to remove burrs. At the same time, an industrial endoscope is used to check the integrity of the inner wall of each vertical hole 14. Accessories such as the high-voltage tap nut 8 are installed to complete the overall preparation.

[0083] To quantitatively verify the superior performance of the technical solution described in this invention, a detailed data demonstration is provided below through a set of specific embodiments and comparative examples.

[0084] Example 1: This embodiment adopts the structural scheme and preparation method described in this invention. The thickness of the high-pressure casting body 1 is set to 4 mm, 15 wt% of nano-alumina filler is added to the resin matrix, and the width of the air channel 11 is 10 mm. It is prepared by the above six-step process.

[0085] Example 2: This embodiment is basically the same as Embodiment 1, except that 12wt% of nano-aluminum nitride filler is added to the resin matrix, and the cross-section of the vertical hole 14 is set to a wider oval shape.

[0086] Comparative Example 1: The windings prepared using the traditional casting process do not have vertical holes on the high-voltage side or air passages on the low-voltage side. The resin matrix is ​​conventional pure epoxy resin (without added high thermal conductivity fillers), and a conventional one-stage high-temperature curing process is used.

[0087] The experimental conditions were strictly implemented in accordance with the GB / T 1094.11 standard, and the experimental test data comparison results are shown in Table 1.

[0088] Table 1: Test Data Table The data comparison in Table 1 clearly demonstrates the technical solution described in this invention: In terms of electrical insulation performance, due to the use of integrated casting and precise thickness control, the partial discharge of the embodiment is controlled to an extremely low level of less than 3pC, which is far superior to Comparative Example 1. This directly indicates the high reliability of the winding under long-term high-voltage operation.

[0089] In terms of heat dissipation performance, thanks to the synergistic effect of high thermal conductivity filler and longitudinal / annular heat dissipation channels, the thermal conductivity of the embodiment is effectively improved, resulting in a significant reduction of temperature rise under rated load by more than 30K. This means that under the same heat dissipation conditions, the winding described in this invention has good overload capacity.

[0090] In terms of mechanical properties, the combination of the insulating cylinder 2 and the longitudinal rigid support structure effectively improves the axial strength, and in the simulated short-circuit impact test, the radial deformation is compressed to a very small range, which fully demonstrates its mechanical reliability.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An epoxy resin winding for a dry-type transformer, characterized in that, From the outside to the inside, it includes a high-pressure casting body (1), an insulating cylinder (2), and a low-pressure casting body (3); The high-pressure casting body (1) is cast and formed on the outside of the high-voltage coil, including the high-voltage epoxy resin winding (4). Several axially penetrating vertical holes (14) are evenly distributed in the high-voltage epoxy resin winding (4) along the circumferential direction. The cross-section of the vertical holes (14) is long ellipse or waist-shaped, and the long axis of the vertical holes (14) is arranged along the radial direction of the high-voltage epoxy resin winding (4). The insulating cylinder (2) is concentrically positioned between the high-pressure casting body (1) and the low-pressure casting body (3); The low-pressure casting body (3) is cast and formed on the outside of the low-pressure coil, including multiple interconnected and integrally formed low-pressure epoxy resin rings (13). An air channel (11) is reserved between two adjacent layers of low-pressure epoxy resin rings (13), and several air channel support strips (12) are arranged alternately along the circumferential direction in the air channel (11).

2. The epoxy resin winding for a dry-type transformer according to claim 1, characterized in that, The high-pressure casting body (1) also includes a high-pressure outer insulation layer (5) located outside the high-pressure epoxy resin winding (4) and a high-pressure inner insulation layer (6) located inside the high-pressure epoxy resin winding (4); and the high-pressure outer insulation layer (5), the high-pressure epoxy resin winding (4) and the high-pressure inner insulation layer (6) are integrally formed by the same vacuum casting cycle.

3. The epoxy resin winding for a dry-type transformer according to claim 1, characterized in that, A turbulence unit array (19) is formed on the inner surface of the vertical hole (14), and the turbulence unit array (19) is arranged in a spiral upward manner along the axial direction of the vertical hole (14).

4. The epoxy resin winding for a dry-type transformer according to claim 1, characterized in that, The airway support strip (12) has a hollow structure. A support rib (22) is provided inside the airway support strip (12) and connected to the side wall of the airway support strip (12). The internal chamber of the airway support strip (12) is divided into multiple buffer chambers (21) by the support rib (22). The buffer chambers (21) are connected to the airways (11) on both sides respectively. The support rib (22) extends continuously in a sinusoidal wave shape along the length of the airway support strip (12).

5. The epoxy resin winding for a dry-type transformer according to claim 1, characterized in that, The air duct support strips (12) are staggered in the circumference of the two adjacent air ducts (11); and the inner insulation (9) and outer insulation (10) are integrally cast on the inner and outer sides of the low-pressure casting body (3), respectively. The inner insulation (9) and outer insulation (10) are respectively provided with connecting grooves for covering the connection parts of the low-pressure inner copper busbar (16) and the low-pressure outer copper busbar (15); the upper part of the high-pressure epoxy resin winding (4) is integrally cast with a high-pressure tap nut seat (7), and the high-pressure tap nut (8) is encapsulated inside the high-pressure tap nut seat (7).

6. A method for preparing epoxy resin windings for dry-type transformers as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Coil winding and pre-positioning; Step 2: Mold assembly. Place the wound coil into the casting mold for positioning and seal the mold. Step 3: Vacuum preheating treatment; Step 4: Vacuum pressure casting: Inject the epoxy resin mixture and apply dry nitrogen pressure of 0.3MPa to 0.5MPa for impregnation; Step 5: Step curing: Hold at 80℃ for 12 hours, raise the temperature to 100℃ and hold for 4 hours, then raise the temperature to 130℃ and hold for 6 hours, and finally cool naturally; the heating rate is 1.5℃ / min. Step Six: Perform demolding and post-processing.

7. The method for preparing epoxy resin windings for dry-type transformers according to claim 6, characterized in that, In step one, when the coil is wound, if the coil structure is a double-layer cylindrical structure, the double-layer cylindrical coil winding method is used during the winding process; if the coil structure is a multi-layer cylindrical structure, the multi-layer cylindrical coil winding method is used during the winding process.

8. A method for preparing epoxy resin windings for dry-type transformers according to claim 7, characterized in that, When using the double-layer cylindrical coil winding method, at halfway through the winding of one layer, the cross positions of the wires are interchanged to balance the electromagnetic distribution, and the insulating paper between the layers is staggered by 10mm to 15mm; when using the multi-layer cylindrical coil winding method, a layer of insulating adhesive paper is first wound on the insulating cylinder (2) before winding.

9. A method for preparing epoxy resin windings for dry-type transformers according to claim 6, characterized in that, Step three, the vacuum preheating process, includes: The assembled mold is placed into a vacuum casting tank, and the vacuum pump is started to reduce the pressure inside the tank to below 100Pa and raise the temperature to 80 to 100℃. Maintained in a high-temperature vacuum environment for 4 to 6 hours; Preheat the resin mixture and the curing agent mixture separately in an oven, then place them in their respective preheating tanks and maintain vacuum degassing for 2 to 4 hours, with the stirring speed controlled at 30 revolutions per minute to remove micro-bubbles from the mixture.

10. A method for preparing epoxy resin windings for dry-type transformers according to claim 6, characterized in that, In step four, the temperature of the final mixing tank is raised to 65 to 70°C two hours before pouring, and the pouring rate is controlled to be within 50 kg per hour for each pouring head. After pouring, vacuuming continues until the bubbles disappear.

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