A megawatt high-voltage-resistant intermediate-frequency isolation transformer

Abstract

The application discloses a megawatt high-voltage intermediate frequency isolation transformer, which comprises a core, a winding and an insulation mechanism; the core is stacked by oriented silicon steel sheets; the winding is wound on the core; and the insulation mechanism comprises insulation paper, an end sealing layer, an insulation bottom cylinder and a primary and secondary side separation plate. The megawatt high-voltage intermediate frequency isolation transformer has good insulation performance, meets the insulation requirement of AC 50KV, has strong heat dissipation capacity, and limits the water temperature rise to below 60 DEG C; and has the advantages of high-efficiency transmission, low temperature rise, high voltage resistance and low noise.

Description

Technical Field

[0001] This invention belongs to the field of transformer design technology, and specifically relates to a megawatt-class high withstand voltage medium frequency isolation transformer. Background Technology

[0002] Medium frequency isolation transformers are mainly used in bidirectional active full-bridge (DAB) operation, such as... Figure 1 As shown, it is placed between full-bridge H1 and H2, and both the primary and secondary sides of full-bridge H1 and H2 generate square wave voltages with a duty cycle of 50%. The transformer port outputs a square wave voltage with an amplitude of 2000-2500V. A trapezoidal current flows through the transformer, with an effective current value of 500-600A. The transformer capacity reaches 1.5MVA per unit, and the operating frequency is between 500-1000Hz. Furthermore, considering the transformer's operating environment, its withstand voltage level is also very high; the requirements for primary and secondary insulation, primary-to-ground insulation, and secondary-to-ground insulation all meet AC50KV. Currently, there are no megawatt-level medium-frequency isolation transformers with such high isolation levels produced, nor are there any relevant manufacturing specifications.

[0003] On the one hand, the megawatt-level capacity and 500-1000Hz operating frequency of transformers result in significant losses, while the heat dissipation area of ​​a single transformer is limited, making heat dissipation design crucial. On the other hand, the transformer operates under DAB conditions in power grid systems (DC voltage can reach up to 20KV). Although the rated voltage is 2000V, a single transformer can withstand voltages as high as 20KV. Furthermore, the voltage across the transformer is a square wave with a 50% duty cycle, resulting in a large du / dt ratio, thus placing high demands on insulation. Current manufacturing standards are not well-suited for the design and fabrication of such transformers. Therefore, there is an urgent need to develop a megawatt-level high-voltage intermediate-frequency isolation transformer to overcome the problems of poor insulation and heat dissipation in existing transformers. Summary of the Invention

[0004] To address the above problems, this invention discloses a megawatt-class high withstand voltage intermediate frequency isolation transformer, comprising: an iron core, windings, and an insulation mechanism;

[0005] The core is made of stacked grain-oriented silicon steel sheets;

[0006] The winding is wound around the iron core;

[0007] The insulation mechanism includes insulating paper, end sealing layer, insulating bottom cylinder, and primary and secondary side partition plates.

[0008] Furthermore, the winding includes a primary winding and a secondary winding;

[0009] The winding is made of a single layer of copper foil;

[0010] The primary winding and the secondary winding are both wound on the same iron core column, with the secondary winding located outside the primary winding.

[0011] Furthermore, an insulating paper is wrapped around the surface of the single-layer copper foil.

[0012] Furthermore, the two ends of the winding are provided with end caps of a set thickness;

[0013] The end-capping material is epoxy resin.

[0014] Furthermore, the lateral and longitudinal distances between the iron core and the primary winding are both set lengths;

[0015] The lateral distance between the iron core and the secondary winding is a set length;

[0016] An insulating bottom cylinder is wound inside the primary winding, and the insulating bottom cylinder is higher than the primary winding.

[0017] Furthermore, a primary-secondary side partition plate is provided between the primary winding and the secondary winding.

[0018] Furthermore, it also includes: a heat dissipation mechanism;

[0019] The heat dissipation mechanism includes a first cold water plate and a second cold water plate;

[0020] Multiple first cold water plates are spaced apart in the iron core.

[0021] Furthermore, the second cooling plate is disposed in the winding and is in direct contact with the copper foil.

[0022] Furthermore, the second cooling plate is higher than the winding.

[0023] Furthermore, the lower ends of the first and second cold water plates are provided with water inlets and water outlets.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1) The transformer has good insulation performance, meeting the insulation requirements of AC50KV, and strong heat dissipation capacity, limiting the water temperature rise to below 60℃;

[0026] 2) It has the advantages of high-efficiency transmission, low temperature rise, high withstand voltage and low noise;

[0027] 3) Power transmission efficiency up to 99%.

[0028] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The operating conditions of a transformer according to an embodiment of the present invention are shown;

[0031] Figure 2 A schematic diagram of a portion of the transformer according to an embodiment of the present invention is shown;

[0032] Figure 3 A schematic diagram of a transformer according to an embodiment of the present invention is shown;

[0033] Figure 4 A diagram showing the arrangement of the first cold water plate according to an embodiment of the present invention is provided;

[0034] Figure 5 A diagram showing the arrangement of the second cold water plate according to an embodiment of the present invention is provided.

[0035] Reference numerals in the attached diagram: 1. Iron core; 2. Winding; 21. Primary winding; 22. Secondary winding; 3. Insulating paper; 4. End sealing layer; 5. Insulating bottom cylinder; 6. Primary and secondary side partition plate; 7. First cooling water plate; 8. Second cooling water plate; 9. Copper foil. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0037] Figure 1 The operating conditions of a transformer according to an embodiment of the present invention are shown. For example... Figure 1As shown, the insulation requirements for transformers applied to DAB operating conditions are: insulation between the primary winding 21 and the secondary winding 22, insulation between the primary winding 21 and ground (core 1), and insulation between the secondary winding 22 and ground (core 1) reach AC50KV; insulation class: H class (180℃).

[0038] The transformer is positioned between bridges H1 and H2. Both the primary and secondary sides of bridges H1 and H2 generate square wave voltages with a 50% duty cycle. The transformer terminals produce square wave voltages with an amplitude of 2000-2500V. A trapezoidal current flows through the transformer, with an effective current value of 500-600A. The transformer has a capacity of 1.5MVA per unit and operates at a frequency between 500-1000Hz.

[0039] Figure 2 A schematic diagram of a portion of a transformer according to an embodiment of the present invention is shown. Figure 2 As shown, in view of the insulation requirements and insulation class of transformers applied to DAB operating conditions, the present invention proposes a megawatt-class high withstand voltage medium frequency isolation transformer, including: iron core 1, winding 2, insulation mechanism and heat dissipation mechanism;

[0040] The iron core 1 is made of stacked oriented silicon steel sheets;

[0041] The winding 2 is wound on the iron core 1;

[0042] The insulation mechanism includes insulating paper 3, end sealing layer 4, insulating bottom cylinder 5, and primary and secondary side partition plate 6;

[0043] The heat dissipation mechanism includes a first cold water plate 7 and a second cold water plate 8.

[0044] like Figure 3 As shown, winding 2 includes primary winding 21 and secondary winding 22;

[0045] The winding 2 is made of a single layer of copper foil 9. The primary winding 21 and the secondary winding 22 are both wound on the same iron core column, with the primary winding 21 on the inner side and the secondary winding 22 on the outer side. The transformer includes two iron cores 1, both of which adopt the same winding structure. The primary windings 21 on the two iron core columns are connected in series with each other, and the secondary windings 22 are connected in series with each other.

[0046] The two ends of the winding 2 are provided with end sealing layers 4 of a set thickness.

[0047] Inter-turn insulation: Inter-turn insulation between windings 2 is achieved using insulating paper 3 and epoxy resin injection. A layer of insulating paper 3 is pre-wound onto a single layer of copper foil 9 using a foil winding machine. Preferably, the thickness of the insulating paper 3 is 0.15 mm, capable of withstanding several kilovolts, before winding 2 is wound. After winding 2 is completed, end-sealing layers 4 of a predetermined thickness are provided at the upper and lower ends of winding 2. Specifically, end-sealing layers 4 are formed by casting epoxy resin three times on both sides of the upper and lower ends of winding 2, sealing the upper and lower openings of winding 2. The thickness of end-sealing layer 4 is preferably 30 mm. By providing end-sealing layers 4 at the upper and lower ends of winding 2, the creepage distance can be increased, enhancing the insulation characteristics of winding 2.

[0048] The lateral and longitudinal distances between the iron core 1 and the primary winding 21 are both set lengths;

[0049] The lateral distance between the iron core 1 and the secondary winding 22 is a set length; preferably, the set length is 60mm.

[0050] An insulating bottom cylinder 5 is wound inside the primary winding 21, and the insulating bottom cylinder 5 is higher than the primary winding 21.

[0051] Insulation between primary winding 21 and core 1: The transformer insulation requirement is AC50KV, therefore, an insulation distance of 60mm is set according to relevant manufacturing specifications. This insulation distance is the length of the air gap, and the lateral and longitudinal distances between the primary winding 21 and core 1 are both set to 60mm. Furthermore, considering the possibility of highly non-uniform electric fields, a 6mm thick insulating base cylinder 5 is wound inside the primary winding 21. The insulating base cylinder 5 has strong withstand voltage; 1mm can withstand tens of thousands of volts. Simultaneously, the insulating base cylinder 5 is higher than the primary winding 21, increasing the creepage distance and effectively suppressing creepage breakdown.

[0052] Insulation between secondary winding 22 and core 1: Given that secondary winding 22 is on the outside, the longitudinal distance meets the insulation requirements; the lateral distance between secondary winding 22 and core 1 is set to 60mm.

[0053] A primary-secondary side partition plate 6 is provided between the primary winding 21 and the secondary winding 22. The primary-secondary side partition plate 6 is an insulating and withstand voltage plate inserted between the primary winding 21 and the secondary winding 22, and is fixed by inserting small epoxy resin modules.

[0054] Insulation between primary winding 21 and secondary winding 22: The transformer insulation requirement is AC50KV, therefore a 60mm air gap insulation distance is set according to relevant manufacturing specifications. Simultaneously, a 4mm thick primary-secondary side partition plate 6 is installed in the middle of the gap between primary winding 21 and secondary winding 22. The 1mm thick partition plate 6 can withstand tens of thousands of volts, enhancing insulation through insulation coordination and increasing creepage distance to suppress creepage breakdown. To further enhance insulation, after the basic winding 2 is wound, more than 10 layers of insulating paper 3, higher than the winding 2, are wrapped around the outside of winding 2.

[0055] Under the above insulation design of the transformer, after electric field simulation and withstand voltage test, no flashover, breakdown or arcing phenomena were found. It can be concluded that: under this insulation design, the insulation between the primary winding 21 and the secondary winding 22, the insulation between the primary winding 21 and the ground (core 1), and the insulation between the secondary winding 22 and the ground (core 1) fully meet the insulation requirements of AC50KV. The insulation performance is good, which can effectively insulate and ensure the long-term stable operation of the transformer, and significantly reduce the failure of the transformer caused by weak insulation.

[0056] The heat dissipation mechanism includes a first cooling plate 7 and a second cooling plate 8;

[0057] Multiple first cold water plates 7 are spaced apart in the iron core 1.

[0058] Core 1 heat dissipation: Many dry-type transformers typically use natural heat dissipation, but this method is clearly unsuitable for such ultra-large capacity transformers. Considering the operating environment and heat dissipation requirements of this type of transformer, this invention employs a water-cooled plate cooling system for core 1 heat dissipation.

[0059] Figure 4 A diagram showing the arrangement of a first cold water plate according to an embodiment of the present invention is provided. Figure 4 As shown, the first cooling plate 7 is arranged as follows: the core 1 is a laminated core of grain-oriented silicon steel sheets, and the first cooling plate 7 is arranged within the core 1. The arrangement position is determined by analyzing the temperature rise of various parts of the core 1 using ICEPAK simulation. Preferably, the final position of the first cooling plate 7 is determined as: 1 / 4 thickness core 1 + first cooling plate 7 + 1 / 2 thickness core 1 + first cooling plate 7 + 1 / 4 thickness core 1. This ensures that the thermal resistance from the outermost core 1 to the first cooling plate 7 is uniform, which can significantly reduce the temperature of local areas of the core 1 and avoid overheating in local areas of the core 1.

[0060] The second cooling plate 8 is located at the center of the winding 2 and is in direct contact with the copper foil 9; the second cooling plate 8 is higher than the winding 2.

[0061] The cold water plate includes a first cold water plate 7 and a second cold water plate 8, both of which have the same structure. The lower ends of the first cold water plate 7 and the second cold water plate 8 are provided with water inlets and water outlets.

[0062] Figure 5 A diagram showing the arrangement of a second cold water plate according to an embodiment of the present invention is provided. Figure 5 As shown, cooling of winding 2: The transformer uses copper foil winding 2, so a direct water-cooling method cannot be used. Therefore, cooling of winding 2 also adopts a cold water plate cooling method. The layout of the second cold water plate 8 is shown in the figure. Figure 5 As shown, the darker area on winding 2 indicates the installation location of the second cooling plate 8. The second cooling plate 8 is positioned in the middle region of winding 2, ensuring consistent thermal resistance between the outermost copper foil 9 and the second cooling plate 8. This arrangement significantly reduces the temperature in localized areas of winding 2, preventing overheating. Due to the inter-turn insulation of winding 2, the installation of the second cooling plate 8 requires special attention. The position of the second cooling plate 8 should be carefully arranged according to the position of the inter-turn insulation paper 3. In this transformer, the second cooling plate 8 will be slightly higher than winding 2; preferably, it should be about 1 cm higher. This prevents damage to the inter-turn insulation when replacing the cooling plate interface. Furthermore, the aluminum second cooling plate 8 does not have additional insulation paper 3 between it and the copper foil 9, allowing direct contact for heat dissipation.

[0063] Water pipe layout and flow resistance pressure holding experiment: Deionized water from the water pump flows into the cooling water plate through water pipes around the transformer. For example, the transformer uses eight cooling water plates, all with cooling water flowing in from the lower inlet and out from the lower outlet, increasing the heat dissipation efficiency of the cooling water plates. Simultaneously, a centralized water interface is installed on both sides of the transformer, located below the cooling water plates, facilitating water pump connection. Although the above description uses eight cooling water plates as an example to illustrate the transformer's heat dissipation design, the present invention is not limited to this; it can use different numbers of cooling water plates, such as six, ten, or twelve. Those skilled in the art can comprehensively consider the actual application situation based on the heat dissipation design principles and structure of the present invention, as long as the principle of the present invention can be achieved.

[0064] Since a water-cooled plate cooling method is used, it is essential to ensure that the water-cooling circuit is sufficiently airtight and has strong stability under water pressure. Therefore, a flow resistance and pressure holding test was specifically conducted to meet these requirements.

[0065] Flow resistance test: Measure the obstruction of water flow by the transformer's water cooling circuit, and determine the required water pressure to ensure the target flow velocity.

[0066] Method: Given a flow rate, calculate the pressure difference between the inlet and outlet; the difference is the flow resistance value.

[0067] result:

[0068] Tests showed that a water flow rate of 15 L / min could be maintained at a water pressure of 0.39 bar.

[0069] Tests showed that a water flow rate of 20 L / min could be maintained at a water pressure of 0.58 bar.

[0070] Tests showed that a water flow rate of 25 L / min could be maintained at a water pressure of 0.77 bar.

[0071] Tests showed that a water flow rate of 30 L / min could be maintained at a water pressure of 1.03 bar.

[0072] At a water pressure of 0.77 bar, the cooling water flow rate can reach 25 L / min, which meets the requirements.

[0073] Pressure holding test: to check whether the transformer water cooling circuit leaks and the stability of water pressure.

[0074] The water system showed no leakage for 30 minutes under a water pressure of 1 MPa, with little change in pressure (1 MPa = 10 bar).

[0075] Initial water pressure: 10.8 bar;

[0076] Stable water pressure: 9.7 bar. The pressure value changes little, proving that the transformer water cooling circuit meets the requirements.

[0077] Transformer heat dissipation performance: After physical stress testing and simulation comparison, the transformer, after reaching thermal equilibrium, exhibits a maximum temperature of approximately 95℃ for core 1, with a water temperature rise of 59.8℃ and an air temperature rise of 68.9℃. The maximum temperature for transformer winding 2 is 81.8℃, with a water temperature rise of 46.6℃ and an air temperature rise of approximately 55℃. Furthermore, thermal imaging revealed no localized overheating in core 1 or winding 2, indicating that the transformer's H-class insulation will not fail. Therefore, the heat dissipation design effectively meets the transformer's cooling requirements, preventing accelerated aging of transformer components due to high temperatures and ensuring long-term stable operation.

[0078] Power transmission efficiency: Using the megawatt-class high-voltage intermediate-frequency isolation transformer designed above for power transmission, the transmission power can reach 1.5MVA, with iron losses of approximately 7600W and copper losses of approximately 4000W. Calculations show that the transmission efficiency is as high as 99% or more. The transformer has the advantages of high-efficiency transmission, low temperature rise, high withstand voltage, and low noise.

[0079] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A megawatt-class high-voltage intermediate-frequency isolation transformer, characterized in that, include: Iron core (1), windings (2) and insulation mechanism; The iron core (1) is made of stacked oriented silicon steel sheets; The winding (2) is wound on the iron core (1); The insulation mechanism includes insulating paper (3), end sealing layer (4), insulating bottom cylinder (5) and primary and secondary side partition plate (6). The winding (2) includes a primary winding (21) and a secondary winding (22). The winding (2) is made of a single layer of copper foil (9); The primary winding (21) and the secondary winding (22) are both wound on the same iron core column, with the secondary winding (22) located outside the primary winding (21); The surface of the single-layer copper foil (9) is wrapped with a layer of insulating paper (3). The lateral and longitudinal distances between the iron core (1) and the primary winding (21) are both set lengths; The lateral distance between the iron core (1) and the secondary winding (22) is a set length; An insulating bottom cylinder (5) is wound inside the primary winding (21), and the insulating bottom cylinder (5) is higher than the primary winding (21). A primary-secondary side partition plate (6) is provided between the primary winding (21) and the secondary winding (22). The winding (2) is surrounded by an insulating paper (3) that is higher than the winding (2). It also includes: heat dissipation mechanisms; The heat dissipation mechanism includes a first cold water plate (7) and a second cold water plate (8); Multiple first cold water plates (7) are spaced apart in the iron core (1); The second cold water plate (8) is disposed in the winding (2) and is in direct contact with the copper foil (9); The second cooling plate (8) is higher than the winding (2); The winding (2) has end caps (4) of a set thickness at both ends.

2. The megawatt-class high-voltage intermediate-frequency isolation transformer according to claim 1, characterized in that, The end cap (4) is made of epoxy resin.

3. The megawatt-class high-voltage intermediate-frequency isolation transformer according to claim 1, characterized in that, The lower ends of the first cold water plate (7) and the second cold water plate (8) are provided with water inlet and water outlet.

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