Oil-immersed transformer

Abstract

The invention belongs to the technical field of power equipment, and particularly relates to an oil-immersed transformer which comprises an oil tank, an iron core winding assembly and an efficient heat dissipation assembly, all the assemblies are nested and linked through a solid structure to form a collaborative system, and the iron core winding assembly adopts a gradient magnetic conductance laminated core and a concentric sectional winding; the efficient heat dissipation assembly comprises an embedded heat dissipation pipe, a circulating oil pump and double-layer annular heat dissipation fins, and oil liquid three-dimensional circulation is achieved through cooperation of the efficient heat dissipation assembly and the conical flow guide plates which are vertically symmetrical. According to the iron core assembly, through layered design and air gap optimization of different magnetic conductive materials, magnetic flux distribution is more uniform, magnetic hysteresis loss and eddy current loss are reduced, the operation efficiency is improved, meanwhile, the winding structure adopts double-layer insulation, the insulation strength is enhanced, the heat dissipation effect of the winding is improved, and the service life of the winding is prolonged. Through the synergistic effect of the inner heat dissipation fins, the flow guide plate and the spiral heat dissipation oil pipe, heat dissipation circulation is formed, the convection speed of insulating oil is increased, the heat dissipation efficiency is improved, and the replacement period of the insulating oil is prolonged.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, specifically to an oil-immersed transformer. Background Technology

[0002] Oil-immersed transformers are widely used in power transmission systems due to their excellent heat dissipation and high insulation strength. The core structure of existing oil-immersed transformers typically includes an iron core, windings, an oil tank, and a heat dissipation device. The iron core is mostly made of single silicon steel sheets laminated together, and the windings are fitted onto the iron core columns and then immersed in insulating oil.

[0003] However, existing technologies have the following shortcomings: First, the magnetic permeability of the core is unevenly distributed, and large hysteresis losses are easily generated in high magnetic density areas, leading to a decrease in transformer operating efficiency. Second, the insulation structure between the winding and the core is mostly wrapped with a single insulating paper, and the insulation strength is greatly affected by temperature. After long-term operation, it is prone to aging and cracking, posing a risk of insulation breakdown. Third, the heat dissipation circulation of the insulating oil relies on natural convection, resulting in low heat dissipation efficiency. Especially during peak load periods, local hot spots are easily formed inside the tank, accelerating the deterioration of the insulating oil and the aging of the insulation structure. Fourth, the support structure between the core and the tank of traditional transformers lacks stability and is prone to displacement under conditions such as transportation or earthquakes, affecting the safety of equipment operation. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides an oil-immersed transformer that features low loss, high insulation strength, efficient heat dissipation, and high stability, thereby improving equipment reliability and service life. It also solves the problems of poor magnetic loss, insulation performance, heat dissipation efficiency, and structural stability in existing oil-immersed transformers.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0008] An oil-immersed transformer includes an oil tank, a core assembly disposed inside the oil tank, a winding assembly mounted on the core assembly, insulating oil filling an oil cavity inside the oil tank, and a heat dissipation assembly disposed outside the oil tank.

[0009] The core assembly adopts a gradient magnetic permeability laminate structure, including a central magnetic column, an intermediate magnetic yoke layer and an outer magnetic shielding layer arranged sequentially from the inside to the outside;

[0010] Furthermore, the central magnetic column is made of high magnetic induction oriented silicon steel sheets stacked together, with a magnetic induction intensity ≥1.9T;

[0011] The intermediate magnetic yoke layer is made of low-loss oriented silicon steel sheets, with an iron loss value ≤0.2W / kg;

[0012] The outer magnetic shielding layer is made of amorphous alloy strip wound together, with a thickness of 0.1-0.3 mm;

[0013] An air gap is provided between the central magnetic column and the intermediate magnetic yoke layer. An insulating support block is arranged in a ring array within the air gap. The support block has an arc-shaped structure, with a radial thickness consistent with the width of the air gap and an axial height consistent with the segment height of the low-voltage winding. It is uniformly distributed along the circumference. A nanocrystalline alloy sheet is embedded inside the insulating support block. The magnetic permeability of the nanocrystalline alloy sheet is consistent with that of the intermediate magnetic yoke layer. It is used to guide the leakage magnetic field at the air gap to the intermediate magnetic yoke layer.

[0014] The surface of the amorphous alloy strip of the outer magnetic shielding layer is coated with a polyamide-imide insulating coating with a thickness of 10-20 μm.

[0015] The outer magnetic shielding layer is an annular sleeve structure with an axial height lower than the middle magnetic yoke layer. There are pre-reserved gaps at the upper and lower ends, and the gaps are filled with insulating buffer pads. The upper and lower end faces of the outer magnetic shielding layer are attached with annular insulating end plates. The outer diameter of the insulating end plates is the same as the outer diameter of the outer magnetic shielding layer, and the inner diameter is the same as the outer diameter of the middle magnetic yoke layer. The inner edge of the annular insulating end plates is provided with arc-shaped magnetic conductive protrusions, which are evenly distributed along the circumference of the insulating end plates.

[0016] The winding assembly includes a low-voltage winding and a high-voltage winding coaxially nested outside the central magnetic column, and is also provided with a composite insulation structure consisting of a primary insulation layer and a secondary insulation layer.

[0017] Furthermore, the high-voltage winding and the low-voltage winding are coaxially nested on the outside of the central magnetic column, and are precisely adapted to the arc-shaped magnetic groove of the intermediate magnetic yoke layer.

[0018] The high-voltage winding adopts a twisted winding segmented structure, and the low-voltage winding adopts a multi-layer dense winding segmented structure. The number of segments in both is the same and they are aligned vertically. An insulating oil separator with built-in adsorbent silicone particles is set between adjacent segments.

[0019] The main insulating layer has a sandwich structure of "insulating paper-nanocomposite layer-insulating paper". The nanocomposite layer is composed of an epoxy resin matrix and nano-aluminum nitride particles dispersed therein. The particle size of the nano-aluminum nitride particles is 50-100nm, and the amount added is 5-8% of the mass of the epoxy resin matrix.

[0020] The secondary insulating layer is a composite layer of polyimide film and aramid paper with a thickness of 0.2-0.4 mm. Its surface is provided with spiral heat dissipation grooves with a groove depth of 0.05-0.1 mm and a pitch of 5-8 mm.

[0021] The oil tank is equipped with internal heat dissipation fins and a guide plate, which together with the external heat dissipation components form a bidirectional heat dissipation structure.

[0022] Furthermore, the internal heat dissipation fins are evenly distributed along the axial direction of the winding assembly, including a spiral main heat dissipation fin fitted on the outside of the high voltage winding and an axial auxiliary heat dissipation fin fitted on the outside of the intermediate magnetic yoke layer. The main heat dissipation fins are segmented and aligned along the axial direction of the high voltage winding, and the auxiliary heat dissipation fins are evenly distributed circumferentially along the intermediate magnetic yoke layer. The bottom of the trapezoidal cross-section of the main heat dissipation fins is provided with a micro-guide groove to guide the oil to flow along the root of the fin.

[0023] The guide plate is divided into an upper guide plate and a lower guide plate. The upper guide plate is in the shape of an inverted cone and is set at the top of the winding assembly, while the lower guide plate is in the shape of a cone and is set at the bottom of the winding assembly.

[0024] The upper guide plate is fixedly connected between the annular step at the upper end of the middle magnetic yoke layer and the upper end plate of the high voltage winding by insulating bolts, and the lower guide plate is fixedly connected between the lower end plate of the low voltage winding and the annular boss at the bottom of the oil tank.

[0025] The conical surface of the guide plate has a spiral guide groove, the direction of which is consistent with the direction of oil flow, in order to enhance the directional flow of oil.

[0026] The heat dissipation component includes a heat dissipation oil pipe and a heat dissipation fin. The heat dissipation oil pipe is spirally wrapped around the outside of the oil tank. Its inlet is connected to the bottom of the oil tank and its outlet is connected to the top of the oil tank. A matching circulating oil pump is connected in series on the heat dissipation oil pipe. The heat dissipation fin is an aluminum corrugated sheet with diamond-shaped ventilation holes on its surface.

[0027] The support base at the bottom of the core assembly is connected to the bottom of the oil tank through an elastic buffer support.

[0028] Furthermore, the elastic buffer support includes an upper support block, a lower support block, and a disc spring assembly disposed between the two, wherein the disc spring assembly consists of at least two disc springs stacked in opposite directions.

[0029] The upper support block is fixed to the support seat of the iron core assembly, and the lower support block is fixedly connected to the bottom of the oil tank;

[0030] A guide post is provided between the upper support block and the lower support block. The guide post is inserted into the guide hole of the lower support block, and a rubber buffer sleeve is provided in the guide hole.

[0031] Furthermore, the top of the oil tank is equipped with a pressure relief valve, an insulating oil sampling valve, and a high-pressure / low-pressure bushing. The operating pressure of the pressure relief valve is 0.05-0.08 MPa, and the sampling valve is equipped with a filter element with a pore size of 0.2-0.5 μm.

[0032] (III) Beneficial Effects

[0033] Compared with the prior art, the present invention provides an oil-immersed transformer, which has the following advantages:

[0034] This invention utilizes a gradient magnetic core structure with layered design of different magnetic materials and optimized air gap to achieve a more uniform magnetic flux distribution within the core, effectively reducing hysteresis and eddy current losses and improving operating efficiency. Simultaneously, the winding structure employs a nano-reinforced primary insulation layer and a secondary insulation layer with heat dissipation grooves, enhancing both insulation strength and heat dissipation, preventing insulation aging caused by localized overheating. The synergistic effect of internal heat dissipation fins, guide plates, and spiral heat dissipation oil pipes forms a heat dissipation cycle, increasing the convection velocity of the insulating oil within the tank, improving heat dissipation efficiency, effectively slowing down the degradation rate of the insulating oil, and extending its replacement cycle. The elastic buffer support, through a combination of disc springs and rubber buffer sleeves, effectively absorbs vibration and shock during transportation and electromagnetic vibration during operation, while avoiding structural fatigue caused by rigid connections, thus improving the operational stability of the equipment under complex working conditions. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention;

[0036] Figure 2 This is a schematic diagram of the internal structure of the fuel tank in this invention;

[0037] Figure 3 This is a schematic diagram showing the assembly state of the core assembly and winding assembly in this invention;

[0038] Figure 4 This is a schematic diagram of the cross-section of the winding conductor in this invention;

[0039] Figure 5 This is a cross-sectional view of the elastic buffer support in this invention.

[0040] In the diagram: 1. Oil tank; 2. Iron core assembly; 201. Central magnetic column; 202. Intermediate magnetic yoke layer; 203. Outer magnetic shielding layer; 3. Winding assembly; 301. High-voltage winding; 302. Low-voltage winding; 303. Main insulation layer; 304. Secondary insulation layer; 305. Heat dissipation groove; 4. Oil cavity; 5. Heat dissipation assembly; 501. Heat dissipation oil pipe; 502. Heat dissipation fins; 6. Inner heat dissipation fins; 7. Guide plate; 701. Upper guide plate; 702. Lower guide plate; 8. Support seat; 9. Elastic buffer support; 901. Upper support block; 902. Lower support block; 903. Disc spring assembly; 904. Guide column; 905. Rubber buffer sleeve; 10. Pressure relief valve; 11. Sampling valve; 12. High-pressure / low-pressure bushing. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example

[0043] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, one embodiment of the present invention proposes an oil-immersed transformer, including an oil tank 1, a core assembly 2 disposed in the oil tank 1, a winding assembly 3 mounted on the core assembly 2, insulating oil filled in an oil cavity 4 inside the oil tank 1, and a heat dissipation assembly 5 disposed on the outside of the oil tank 1.

[0044] The number of core assemblies 2 inside the oil tank 1 needs to be determined according to the number of phases of the transformer. There are two configurations: one for single-phase and three for three-phase (integrated design with a common yoke). The three main magnetic columns share an integrated structure of a ring-shaped yoke, arranged in an equilateral triangle. The center-to-center distance between adjacent main magnetic columns is the sum of the outer diameter of the outer magnetic shielding layer 203 and 50mm. The core assembly 2 adopts a gradient magnetic permeability laminated structure, including a central magnetic column 201, a middle yoke layer 202, and an outer magnetic shielding layer 203 arranged sequentially from the inside out. The permeability is higher inside and lower outside, and the magnetic reluctance is lower inside and higher outside. This is achieved through the three layers... The nested solid structure enables directional guidance of the magnetic field path, reducing leakage magnetic loss and electromagnetic vibration. The three-layer structure is set coaxially and concentrically, and the total height is adapted to the upper and lower clamps of the iron core winding assembly. The whole structure is in the shape of a stepped cylinder. The radial dimensions of the central magnetic column 201, the middle magnetic yoke layer 202, and the outer magnetic shielding layer 203 increase sequentially. Each layer is fixed by an insulating positioning structure without direct metal contact. The three-layer structure is fixed to the upper and lower clamps by positioning pins and insulating bolts to form an integral iron core structure. In conjunction with the elastic tie rod clamping mechanism, it further suppresses iron core vibration.

[0045] The central magnetic column 201 is made of high magnetic induction oriented silicon steel sheets, with a stacking factor of 0.96 and a magnetic induction intensity ≥1.9T. It is stacked perpendicularly along the magnetic field direction (axial direction), and the alignment error between the stacks is ≤0.1mm. Every 10 layers of stacks form a group, and the groups are coated with a 0.03mm thick nano-level insulating adhesive (composition: epoxy resin + alumina nanoparticles) to enhance the integrity of the stack and prevent vibration and loosening. The central magnetic column 201 has 4 evenly distributed positioning holes (diameter φ8mm, depth 20mm) at the top and bottom, which cooperate with the positioning bosses of the upper and lower clamps to achieve radial fixation.

[0046] The intermediate magnetic yoke layer 202 is made of low-loss oriented silicon steel sheets, with an iron loss value ≤0.2W / kg (50Hz, 1.7T). Eight arc-shaped magnetic grooves are uniformly opened on the annular sidewall. The magnetic grooves are axially continuous, with a groove width w=10mm, a groove depth d=15mm, and an arc curvature radius R=50mm, which matches the magnetic field distribution trajectory and reduces magnetic reluctance abrupt changes. The sheet thickness is 0.35mm, and the sheets are stacked along the annular tangent direction (consistent with the magnetic field tangent direction). The joints of the sheets are joined by a bevel joint. The method (overlap angle 45°) avoids interruption of the magnetic circuit. A 0.04mm thick insulating damping coating (with the same material as the overall damping coating of the iron core, epoxy resin + silicon dioxide nanoparticles) is applied between the laminations to balance insulation and vibration reduction. Annular positioning steps (5mm wide, 2mm high) are set on the upper and lower end faces to cooperate with the annular grooves of the upper and lower clamps. A 0.5mm thick polyimide insulating film is pasted on the inner side wall (the side opposite to the central magnetic column 201) to ensure electrical isolation from the central magnetic column 201.

[0047] The outer magnetic shielding layer 203 is made of amorphous alloy strip wound with a thickness of 0.1-0.3mm. Six axial heat dissipation ribs are evenly distributed on the outer surface. These ribs have a trapezoidal cross-section (8mm wide at the top, 12mm wide at the bottom, and 10mm high). They are integrally laminated with the outer magnetic shielding layer 203, serving both magnetic conductivity and heat dissipation functions. The outer layer uses nanocrystalline alloy strip wound and laminated with a strip thickness of 0.02mm and ≥500 layers. The winding tension is controlled at 5-8N to ensure uniform layer density. ≥7.2g / cm³), no additional insulating layer is required between the layers. Insulation is achieved by utilizing the oxide film of the strip itself (film thickness ≤0.001mm), reducing additional magnetic circuit losses. Annular pressure rings (material: epoxy glass cloth board, thickness 5mm) are set at the top and bottom. They are fixed to the middle magnetic yoke layer 202 by four circumferentially evenly distributed insulating bolts (material: polytetrafluoroethylene, diameter φ6mm). A 0.5mm thick ceramic fiber insulating pad is pasted on the inner wall to avoid forming a conductive circuit with the middle magnetic yoke 202.

[0048] An air gap is provided between the central magnetic column 201 and the intermediate magnetic yoke layer 202. An insulating support block is arranged in a ring array within the air gap. The support block has an arc-shaped structure, with a radial thickness consistent with the width of the air gap and an axial height consistent with the segment height of the low-voltage winding 302. It is evenly distributed along the circumference. A nanocrystalline alloy sheet is embedded inside the insulating support block. The permeability of the nanocrystalline alloy sheet is consistent with that of the intermediate magnetic yoke layer 202. It is used to guide the leakage magnetic field at the air gap to the intermediate magnetic yoke layer 202.

[0049] The outer magnetic shielding layer 203 amorphous alloy strip is coated with a polyamide-imide insulating coating with a thickness of 10-20μm.

[0050] The outer magnetic shielding layer 203 is an annular sleeve structure with an axial height lower than the middle magnetic yoke layer 202. Gaps are reserved at the upper and lower ends, and the gaps are filled with insulating buffer pads made of ceramic fiber with a thickness of 5mm. This prevents the central magnetic column 201 and the middle magnetic yoke layer 202 from forming a conductive circuit with the outer magnetic shielding layer 203 due to vibration. At the same time, it meets the insulation distance requirements inside the transformer. Annular insulating end plates are attached to the upper and lower end faces of the outer magnetic shielding layer 203. The outer diameter of the insulating end plate is the same as the outer diameter of the outer magnetic shielding layer 203, and the inner diameter is the same as the outer diameter of the middle magnetic yoke layer 202. Arc-shaped magnetic conductive protrusions are provided on the inner edge of the annular insulating end plate, and the magnetic conductive protrusions are evenly distributed along the circumference of the insulating end plate.

[0051] The upper and lower ends of the central magnetic column 201 and the intermediate magnetic yoke layer 202 need to be directly attached to the annular common yoke (three-phase configuration) or the upper and lower clamps of the iron core (single-phase configuration) to form a closed magnetic circuit. If the outer magnetic shielding layer 203 covers the ends, it will block the conduction path of the main magnetic circuit, causing a surge in magnetic reluctance. The upper and lower ends need to be equipped with fixed components such as elastic pull rods, positioning pins, and annular pressure rings, with a gap reserved to provide operating space for assembly. At the same time, it is ensured that there is no interference between the elastic pull rod and the outer magnetic shielding layer 203. Meanwhile, the gap provides an axial flow channel for insulating oil, forming a three-dimensional circulation of "radial + axial" with the spiral oil guide groove at the bottom of the oil tank 1 and the heat dissipation oil pipe 501, avoiding heat accumulation at the ends of the central magnetic column 201 and the intermediate magnetic yoke layer 202.

[0052] The winding assembly 3 includes a low-voltage winding 302 and a high-voltage winding 301 coaxially nested outside the central magnetic column 201, and is also provided with a composite insulation structure composed of a main insulation layer 303 and a secondary insulation layer 304.

[0053] Among them, the high voltage winding 301 and the low voltage winding 302 are coaxially nested on the outside of the central magnetic column 201, and are precisely matched with the arc-shaped magnetic groove of the intermediate magnetic yoke layer 202.

[0054] The low-voltage winding 302 adopts a multi-layer densely wound segmented structure. The conductor is densely wound clockwise along the axial direction of the central magnetic column 201. Each winding segment consists of 10-15 layers. An insulating oil-separating plate is set between adjacent segments. The plate is made of epoxy glass cloth with a thickness of 10mm and has built-in honeycomb through holes and adsorption-type silicone particles to achieve segmented heat dissipation and humidity control. All segments are wound clockwise to ensure a uniform magnetic field direction and avoid magnetic field cancellation between segments. Annular end plates are set at the top and bottom. The plates are made of epoxy glass cloth with a thickness of 8mm. The outer diameter matches the outer diameter of the low-voltage winding, and the inner diameter matches the outer diameter of the central magnetic column 201. They are cured together with the winding ends by epoxy resin to suppress axial vibration. The outer side of each winding segment is aligned with the arc-shaped magnetic groove of the middle yoke layer 202 (the groove width is 10mm, which matches the width of the winding segment) to ensure directional coupling of the magnetic field along the magnetic groove and reduce leakage magnetic loss.

[0055] The high-voltage winding 301 adopts a twisted winding segmented structure. The conductor is wound clockwise along the outside of the main insulation layer 303. The twisted winding reduces the electric field concentration at the winding ends. Each segment consists of 8-10 layers of winding. An insulating oil separator (with the same specifications as the low-voltage winding 302, 10mm thick) is also installed between adjacent segments, corresponding one-to-one with the segments of the low-voltage winding 302, forming a segmented structure of "vertical alignment and internal and external coordination". The winding direction is consistent with that of the low-voltage winding 302 to ensure the superposition and enhancement of the main magnetic field and avoid the increase of magnetic reluctance. The outside of the high-voltage winding is wrapped with a semi-conductive shielding layer (volume resistivity 10³-10). 5 Ω・m, thickness 1.5mm), with a 0.3mm thick conductive cloth between the shielding layer and the winding to ensure uniform potential distribution. Spiral heat dissipation fins (aluminum alloy material, thickness 2mm, height 15mm, pitch 50mm) are welded to the outside of the shielding layer and connected to the winding heat dissipation structure. The fins are axially connected and do not block the oil circulation.

[0056] The segmented winding and integrated design of the insulating oil separator achieves heat dissipation zoning. The two segments have the same number and are aligned vertically. An insulating oil separator with built-in adsorbent silica gel particles is set between adjacent segments. The silica gel particles adsorb the insulating oil and moisture, improving the insulation reliability.

[0057] The main insulating layer 303 has a sandwich structure of "insulating paper-nanocomposite layer-insulating paper". The nanocomposite layer is composed of an epoxy resin matrix and nano-aluminum nitride particles dispersed therein. The particle size of the nano-aluminum nitride particles is 50-100nm, and the amount added is 5-8% of the mass of the epoxy resin matrix.

[0058] The secondary insulating layer 304 is a composite layer of polyimide film and aramid paper with a thickness of 0.2-0.4 mm. Spiral heat dissipation grooves 305 are provided on its surface with a groove depth of 0.05-0.1 mm and a pitch of 5-8 mm.

[0059] The oil tank 1 is equipped with internal heat dissipation fins 6 and guide plates 7, which together with the external heat dissipation components 5 form a bidirectional heat dissipation structure.

[0060] The inner heat dissipation fins 6 are evenly distributed along the axial direction of the winding assembly 3, including a spiral main heat dissipation fin fitted on the outside of the high voltage winding 301 and an axial auxiliary heat dissipation fin fitted on the outside of the intermediate magnetic yoke layer 202. The main heat dissipation fins are segmented and aligned along the axial direction of the high voltage winding 301, and the auxiliary heat dissipation fins are evenly distributed circumferentially along the intermediate magnetic yoke layer 202. The bottom of the trapezoidal cross section of the main heat dissipation fins is provided with a micro guide groove to guide the oil to flow along the root of the fin.

[0061] The main heat dissipation fins are not directly fitted onto the core assembly 2 to avoid interfering with the magnetic circuit or obstructing the air gap oil flow. They directly contact the high-voltage winding 301, quickly transferring the heat generated by winding losses to the insulating oil. The spiral structure guides the oil to spiral upwards along the axial direction, increasing the heat exchange area. The auxiliary heat dissipation fins transfer the hysteresis loss heat of the intermediate yoke layer to the oil, while simultaneously agitating the oil flow to prevent the formation of a stagnant zone on the outside of the intermediate yoke layer 202. This forms an "inner-outer" double-layer heat dissipation with the main heat dissipation fins, improving overall heat dissipation efficiency. The bottom layer oil... The oil flows upward through the spiral guide groove at the bottom of the oil tank 1. Part of it flows through the arc-shaped magnetic guide groove (axial) of the intermediate magnetic yoke layer 202 and through the channel between the auxiliary heat dissipation fins. After absorbing heat, it flows upward. The other part enters the inner side of the high-voltage winding 301 through the air gap (radial) between the low-voltage winding 302 and the intermediate magnetic yoke layer 202. Then it flows upward along the spiral channel of the main heat dissipation fins and finally merges with the oil on the side of the auxiliary heat dissipation fins. It flows into the top of the oil cavity 4 and enters the heat dissipation oil pipe 501 for circulation, forming a three-dimensional circulation of "radial penetration + axial spiral guide".

[0062] The guide plate 7 is divided into an upper guide plate 701 and a lower guide plate 702. The upper guide plate 701 is in the shape of an inverted cone and is set at the top of the winding assembly 3. The lower guide plate 702 is in the shape of a cone and is set at the bottom of the winding assembly 3. The cone structure guides the oil to flow in a directional manner and enhances the oil exchange efficiency between the upper and lower parts of the winding.

[0063] The upper guide plate 701 is fixedly connected between the upper annular step of the middle magnetic yoke layer 202 and the upper plate of the high voltage winding 301 by insulating bolts, and the lower guide plate 702 is fixedly connected between the lower plate of the low voltage winding 302 and the annular boss at the bottom of the oil tank 1.

[0064] The conical surface of the guide plate 7 has a spiral guide groove, the direction of which is consistent with the direction of oil flow, in order to enhance the directional flow of oil;

[0065] The heat dissipation component 5 includes a heat dissipation oil pipe 501 and a heat dissipation fin 502. The heat dissipation oil pipe 501 is spirally wrapped around the outside of the oil tank 1. Its inlet is connected to the bottom of the oil tank 1 and its outlet is connected to the top of the oil tank 1. A matching circulating oil pump is connected in series on the heat dissipation oil pipe 501. The circulating oil pump is located in the oil chamber 4 inside the oil tank 1 and is located at the center oil outlet at the bottom of the oil tank 1. The heat dissipation fin 502 is an aluminum corrugated fin with diamond-shaped ventilation holes on its surface.

[0066] The heat dissipation oil pipe 501 is also equipped with a spiral guide vane to enhance the turbulence of the oil and improve the heat exchange efficiency.

[0067] In order to better control the oil circulation, a platinum resistance PT100 temperature sensor can be installed near the winding to monitor the oil temperature in real time. When the oil temperature is below 45℃, the opening degree of the matching temperature control valve (paraffin type) is ≤30% to reduce the circulation flow rate; when the oil temperature is above 65℃, the valve is fully opened (100% opening degree), and the circulation flow rate is increased to 50L / min to ensure that the oil temperature is stable within a safe range.

[0068] The support base 8 at the bottom of the iron core assembly 2 is connected to the bottom of the oil tank 1 through the elastic buffer support 9;

[0069] The elastic buffer support 9 includes an upper support block 901, a lower support block 902, and a disc spring assembly 903 disposed between the two. The disc spring assembly 903 is composed of at least two disc springs stacked in opposite directions.

[0070] The upper support block 901 is fixed to the support seat 8 of the iron core assembly 2, and the lower support block 902 is fixedly connected to the bottom of the oil tank 1;

[0071] A guide post 904 is provided between the upper support block 901 and the lower support block 902. The guide post 904 is inserted into the guide hole of the lower support block 902, and a rubber buffer sleeve 905 is provided in the guide hole.

[0072] The oil tank 1 is equipped with a pressure relief valve 10, an insulating oil sampling valve 11, and a high-pressure / low-pressure bushing 12 at the top. The pressure relief valve 10 has an operating pressure of 0.05-0.08 MPa, and the sampling valve 11 is equipped with a filter element with a pore size of 0.2-0.5 μm.

[0073] The specific working process of this transformer is as follows:

[0074] The power system current passes through the high-voltage / low-voltage bushing 12 at the top of the oil tank and is connected to the high-voltage winding 301 and low-voltage winding 302 of the transformer, respectively. After the current is introduced, the winding immediately generates an alternating magnetic field and starts the energy conversion preparation.

[0075] In the initial stage, the winding assembly 3 and the core assembly 2 begin to slowly heat up due to electromagnetic induction. The heat is gradually transferred to the surface insulation layer, and at the same time, the insulating oil in the oil tank 1 is slightly preheated and begins to flow slowly and naturally.

[0076] The alternating magnetic field generated by the winding preferentially acts on the central magnetic column 201. The central magnetic column 201 bears more than 90% of the main magnetic field flux, realizing efficient magnetic field conduction and completing the initial conversion of "electrical energy → magnetic field energy".

[0077] The edge magnetic field of the central magnetic column 201 is smoothly transitioned through the intermediate magnetic yoke layer 202. The arc-shaped magnetic groove of the intermediate magnetic yoke layer 202 precisely guides the magnetic field to couple with the segmented winding, reducing magnetic reluctance abrupt changes and improving magnetic coupling efficiency.

[0078] Leakage magnetic field not absorbed by the main magnetic circuit is absorbed by the outer magnetic shielding layer 203 to prevent leakage magnetic field from spreading to the oil tank 1 or surrounding components and causing eddy current loss.

[0079] In a three-phase configuration scenario, the magnetic fields of the three iron core units form a closed magnetic circuit through the upper and lower annular common magnetic yokes. The three-phase magnetic circuits are symmetrically distributed to ensure the balance of the three-phase current. Finally, the "magnetic field energy → electrical energy" conversion is completed through magnetic field coupling, and stable power is output through the low-voltage winding 302 and the low-voltage bushing.

[0080] The spiral oil guide groove of the arc-shaped guide seat at the bottom of oil tank 1 guides the low-temperature insulating oil at the bottom of oil chamber 4 to the lower part of the winding, and then distributes it evenly to all sides through the lower conical guide plate 702:

[0081] A portion of the oil flows along the conical surface of the lower guide plate 702 to the arc-shaped magnetic groove of the middle magnetic yoke layer 202, absorbing the hysteresis loss heat of the middle magnetic yoke layer 202.

[0082] Another part of the oil enters the inside of the low-voltage winding 302 through the air gap formed by the insulating support block between the low-voltage winding 302 and the intermediate magnetic yoke layer 202, and absorbs the copper loss heat of the low-voltage winding 302.

[0083] After absorbing heat, the oil continues to flow upward, with a portion flowing through the axial auxiliary heat dissipation fins on the outside of the middle magnetic yoke layer 202. The heat is quickly conducted to the main body of the oil through the fins, while the fins disturb the oil flow to prevent stagnation.

[0084] Another portion of the oil passes through the segment gap of the low-voltage winding 302 and enters the air gap of the main insulation layer, absorbing the heat loss from the copper of the high-voltage winding 301, and the oil temperature gradually increases.

[0085] The heated oil flows upward to the upper part of the winding and converges through the upper inverted conical guide plate 701;

[0086] A portion of the oil flows along the conical surface of the upper guide plate 701 to the spiral main heat dissipation fins on the outside of the high-voltage winding 301. The spiral structure guides the oil to rise axially in a spiral manner, increasing the heat exchange area and quickly dissipating heat.

[0087] Another portion of the oil flows to the top of oil chamber 4;

[0088] The oil at the top of the oil chamber 4 is drawn by the circulating oil pump and sent into the cooling oil pipe 501. The spiral guide vanes in the cooling oil pipe 501 enhance heat exchange, and the heat of the oil is transferred to the outside of the oil tank 1 to achieve cooling.

[0089] The cooled oil flows back to the bottom of the oil chamber through the outlet of the heat dissipation oil pipe 501, forming a closed loop.

[0090] If the transformer is overloaded or malfunctions, causing a sudden rise in temperature and pressure inside the oil tank 1, when the pressure exceeds the set value of 0.05MPa, the aluminum foil explosion-proof membrane of the pressure relief valve 10 at the top of the oil tank 1 will rupture, quickly releasing pressure and preventing the oil tank 1 from deforming or being damaged.

[0091] When shutting down, the power input to the high-voltage bushing is cut off, the winding stops generating a magnetic field, energy conversion ends, the heat dissipation components and insulation protection components stop simultaneously, and the oil gradually cools down naturally to the ambient temperature.

[0092] Oil samples can be collected and the status of insulating oil monitored through the quick-connect type oil sampling valve 11 on oil tank 1 without draining the insulating oil.

[0093] When internal components need to be inspected, open the side access door, remove the insulating bolts to take out the core winding assembly, and then carry out the inspection and maintenance.

[0094] After the component maintenance is completed, the iron core winding assembly is installed back into oil tank 1, insulating oil is added to the standard level, and oil tank 1 is sealed before it can be put back into operation.

[0095] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An oil-immersed transformer, comprising an oil tank (1), a core assembly (2) disposed within the oil tank (1), a winding assembly (3) mounted on the core assembly (2), insulating oil filling an oil cavity (4) inside the oil tank (1), and a heat dissipation assembly (5) disposed outside the oil tank (1), characterized in that: The core assembly (2) adopts a gradient magnetic permeability laminate structure, including a central magnetic column (201), an intermediate magnetic yoke layer (202) and an outer magnetic shielding layer (203) arranged sequentially from the inside to the outside. The winding assembly (3) includes a low-voltage winding (302) and a high-voltage winding (301) coaxially nested outside the central magnetic column (201), and is also provided with a composite insulation structure composed of a main insulation layer (303) and a secondary insulation layer (304); The oil tank (1) is equipped with internal heat dissipation fins (6) and a flow guide plate (7), which together with the external heat dissipation components (5) form a bidirectional flow heat dissipation structure. The support base (8) at the bottom of the core assembly (2) is connected to the bottom of the oil tank (1) through an elastic buffer support (9).

2. The oil-immersed transformer according to claim 1, characterized in that: The central magnetic column (201) is made of high magnetic induction oriented silicon steel sheets stacked together, with a magnetic induction intensity ≥1.9T; The intermediate magnetic yoke layer (202) is made of low-loss oriented silicon steel sheets with an iron loss value ≤0.2W / kg; The outer magnetic shielding layer (203) is made of amorphous alloy strip wound together, with a thickness of 0.1-0.3 mm; An air gap is provided between the central magnetic column (201) and the intermediate magnetic yoke layer (202). An insulating support block is arranged in a ring array within the air gap. The support block has an arc-shaped structure, with its radial thickness consistent with the width of the air gap and its axial height consistent with the segment height of the low-voltage winding (302). It is evenly distributed along the circumference. A nanocrystalline alloy sheet is embedded inside the insulating support block. The permeability of the nanocrystalline alloy sheet is consistent with that of the intermediate magnetic yoke layer (202), which is used to guide the leakage magnetic field at the air gap to the intermediate magnetic yoke layer (202).

3. An oil-immersed transformer according to claim 2, characterized in that: The amorphous alloy strip of the outer magnetic shielding layer (203) is coated with a polyamide-imide insulating coating with a thickness of 10-20 μm. The outer magnetic shielding layer (203) is an annular sleeve structure with an axial height lower than that of the middle magnetic yoke layer (202). There are gaps at the upper and lower ends, and the gaps are filled with insulating buffer pads. The upper and lower end faces of the outer magnetic shielding layer (203) are attached with annular insulating end plates. The outer diameter of the insulating end plates is the same as the outer diameter of the outer magnetic shielding layer (203), and the inner diameter is the same as the outer diameter of the middle magnetic yoke layer (202). The inner edge of the annular insulating end plates is provided with arc-shaped magnetic conductive protrusions, which are evenly distributed along the circumference of the insulating end plates.

4. An oil-immersed transformer according to claim 1, characterized in that: The high-voltage winding (301) and the low-voltage winding (302) are coaxially nested on the outside of the central magnetic column (201) and are precisely matched with the arc-shaped magnetic groove of the intermediate magnetic yoke layer (202). The high voltage winding (301) adopts a twisted winding segmented structure, and the low voltage winding (302) adopts a multi-layer dense winding segmented structure. The number of segments of the two are the same and they are aligned vertically. An insulating oil separator with built-in adsorbent silicone particles is set between adjacent segments. The main insulating layer (303) has a sandwich structure of "insulating paper-nanocomposite layer-insulating paper". The nanocomposite layer is composed of an epoxy resin matrix and nano-aluminum nitride particles dispersed therein. The particle size of the nano-aluminum nitride particles is 50-100nm, and the amount added is 5-8% of the mass of the epoxy resin matrix. The secondary insulating layer (304) is a composite layer of polyimide film and aramid paper with a thickness of 0.2-0.4 mm. Its surface is provided with spiral heat dissipation grooves (305) with a groove depth of 0.05-0.1 mm and a pitch of 5-8 mm.

5. An oil-immersed transformer according to claim 1, characterized in that: The inner heat dissipation fins (6) are evenly distributed along the axial direction of the winding assembly (3), including a spiral main heat dissipation fin fitted on the outside of the high voltage winding (301) and an axial auxiliary heat dissipation fin fitted on the outside of the intermediate magnetic yoke layer (202). The main heat dissipation fins are segmented and aligned along the axial direction of the high voltage winding (301), and the auxiliary heat dissipation fins are evenly distributed along the circumference of the intermediate magnetic yoke layer (202). The bottom of the trapezoidal cross section of the main heat dissipation fins is provided with a micro guide groove to guide the oil to flow along the root of the fin. The guide plate (7) is divided into an upper guide plate (701) and a lower guide plate (702). The upper guide plate (701) is in the shape of an inverted cone and is set at the top of the winding assembly (3). The lower guide plate (702) is in the shape of a cone and is set at the bottom of the winding assembly (3). The upper guide plate (701) is fixedly connected between the upper annular step of the middle magnetic yoke layer (202) and the upper plate of the high voltage winding (301) by insulating bolts, and the lower guide plate (702) is fixedly connected between the lower plate of the low voltage winding (302) and the bottom annular boss of the oil tank (1). The conical surface of the guide plate (7) is provided with a spiral guide groove, the direction of which is consistent with the direction of oil flow, in order to enhance the directional flow of oil; The heat dissipation component (5) includes a heat dissipation oil pipe (501) and a heat dissipation fin (502). The heat dissipation oil pipe (501) is spirally wrapped around the outside of the oil tank (1). Its inlet is connected to the bottom of the oil tank (1) and its outlet is connected to the top of the oil tank (1). A matching circulating oil pump is connected in series on the heat dissipation oil pipe (501). The heat dissipation fin (502) is an aluminum corrugated sheet with diamond-shaped ventilation holes on its surface.

6. An oil-immersed transformer according to claim 1, characterized in that: The elastic buffer support (9) includes an upper support block (901), a lower support block (902), and a disc spring assembly (903) disposed between the two. The disc spring assembly (903) consists of at least two disc springs stacked in opposite directions. The upper support block (901) is fixed to the support seat (8) of the iron core assembly (2), and the lower support block (902) is fixedly connected to the bottom of the oil tank (1); A guide post (904) is provided between the upper support block (901) and the lower support block (902). The guide post (904) is inserted into the guide hole of the lower support block (902), and a rubber buffer sleeve (905) is provided in the guide hole.

7. An oil-immersed transformer according to claim 1, characterized in that: The top of the oil tank (1) is equipped with a pressure relief valve (10), an insulating oil sampling valve (11), and a high-pressure / low-pressure bushing (12). The operating pressure of the pressure relief valve (10) is 0.05-0.08MPa, and the sampling valve (11) is equipped with a filter element with a pore size of 0.2-0.5μm.

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