A three-phase three-winding converter transformer suitable for high voltage direct current transmission systems

Abstract

The application provides a three-phase three-winding converter transformer suitable for a high-voltage direct current transmission system, the converter transformer comprising: a transformer oil tank, internally comprising a winding structure immersed in oil, the winding structure comprising a grid-side outgoing line, a valve Y-side outgoing line and a valve D-side outgoing line; a grid-side bushing group comprising three grid-side bushings arranged at the top of the transformer oil tank; a valve-side bushing group comprising three valve Y-side bushings and three valve D-side bushings arranged on the side wall of the transformer oil tank; each valve Y-side bushing and each valve D-side bushing are aligned in the height direction of the transformer oil tank, and the three valve Y-side bushings and the three valve D-side bushings are arranged at intervals along the height direction perpendicular to the transformer oil tank. Through the three-phase three-winding converter transformer provided by the application, the problems of large equipment volume, low integration, complex system structure and high cost of the current converter transformer are solved.

Description

Technical Field

[0001] This application relates to the field of converter transformer technology, and in particular to a three-phase three-winding converter transformer suitable for high-voltage direct current transmission systems. Background Technology

[0002] Transformers, as common and important equipment in power systems, are widely used in AC transmission projects to achieve voltage level conversion. In DC transmission projects, transformers are usually called converter transformers, which connect the AC system to the converter hall, completing the energy transfer and isolation between AC and DC. In existing DC transmission projects, typical converter transformer structures include single-phase two-winding converter transformers, single-phase three-winding converter transformers, and three-phase two-winding converter transformers, which are specifically designed for traditional air-insulated valve halls.

[0003] In engineering applications, air-insulated valve halls rely on air as the insulating medium, and their valve bodies are generally large in size, occupying a large area and having high ceilings. Therefore, single-phase two-winding converter transformers, single-phase three-winding converter transformers, and three-phase two-winding converter transformers are designed primarily to meet capacity requirements and electrical isolation, and are generally characterized by their large size and complex structure.

[0004] A common configuration involves a single-phase multi-unit combination, using six single-phase dual-winding converter transformers or three single-phase three-winding converter transformers to form a three-phase system. This approach generally suffers from large equipment size, low integration, complex system structure, and high cost. To address the shortcomings of the single-phase multi-unit combination, the industry has proposed a three-phase dual-winding converter transformer solution. However, in today's typical converter station configurations, two three-phase dual-winding converter transformers and multiple sets of converter valves are still required to meet the requirements of multi-pulse converter operation. This makes it difficult to further reduce or minimize footprint, system complexity, and construction and maintenance costs, hindering the trend towards more compact and integrated converter stations.

[0005] Therefore, existing converter transformer structures are insufficient to fully meet the urgent needs of DC transmission projects to become more compact, more functionally integrated, and more economical. Utility Model Content

[0006] To address the aforementioned problems, this utility model provides a three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems, thereby solving the issues of large equipment size, low integration, complex system structure, and high cost of current converter transformers.

[0007] This utility model provides a three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems. The technical solution adopted is as follows: A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems, the converter transformer comprising: The transformer tank includes a winding structure immersed in oil, the winding structure including a grid-side outlet, a valve Y-side outlet, and a valve D-side outlet; Cooling mechanisms include natural circulation cooling structures and forced circulation cooling structures; The grid-side bushing assembly includes three grid-side bushings installed on the top of the transformer tank, which are used to lead out the grid-side outgoing lines. The valve side bushing assembly includes a valve Y side bushing assembly and a valve D side bushing assembly disposed on the side wall of the transformer tank. The valve Y side bushing assembly is used to lead out the valve Y side outlet line, and the valve D side bushing assembly is used to lead out the valve D side outlet line. The valve Y-side bushing group includes three valve Y-side bushings, and the valve D-side bushing group includes three valve D-side bushings; each valve Y-side bushing and each valve D-side bushing are aligned one-to-one in the height direction of the transformer tank, and the three valve Y-side bushings and the three valve D-side bushings are respectively spaced apart in the height direction perpendicular to the transformer tank.

[0008] As one of the preferred embodiments, each of the grid-side bushings extends vertically from the top of the transformer tank, and each of the valve Y-side bushings and each of the valve D-side bushings extends horizontally from the side wall of the transformer tank.

[0009] As one of the preferred embodiments, the arrangement direction of the multiple mesh-side sleeves is parallel to the arrangement direction of the multiple valve Y-side sleeves.

[0010] As one of the preferred solutions, the valve Y-side output line is connected to the input terminal of the first group of three-phase six-pulse converter valves using a Y-connection method, and the valve D-side output line is connected to the input terminal of the second group of three-phase six-pulse converter valves using a Δ-connection method.

[0011] As one of the preferred embodiments, the transformer tank has a height of 12.6m, a length of 7.5m, and a width of 5.9m; the spacing between two adjacent valve Y-side bushings is greater than 1.5m; and the spacing between each pair of valve Y-side bushings and valve D-side bushings is 1.5m-2m.

[0012] As one of the preferred solutions, the grid-side bushing, the valve Y-side bushing assembly, and the valve D-side bushing assembly are all fixed on the transformer tank.

[0013] As one preferred embodiment, the inner side of the target sidewall of the transformer tank is provided with two rows of support structures, the target sidewall being the sidewall of the transformer tank where the valve side bushing assembly is located; the two rows of support structures are spaced apart along the height direction of the transformer tank, and the valve Y side bushing assembly is fixed to the upper sidewall of the transformer tank through the upper row of support structures, and the valve D side bushing assembly is fixed to the lower sidewall of the transformer tank through the lower row of support structures.

[0014] As one of the preferred solutions, the winding structure includes multiple iron core columns and a three-phase winding; The plurality of iron core columns include three iron core main columns, and each iron core main column is wound with a corresponding phase winding, the phase winding including a grid-side winding, a voltage regulating winding, a valve Y-side winding and a valve D-side winding; In the radial direction of the core column, the mesh-side winding is located between the valve Y-side winding and the valve D-side winding.

[0015] As one of the preferred options, each of the iron core main columns is wound with a valve Y-side winding, a mesh-side winding, a voltage regulating winding and a valve D-side winding in sequence from the radial inner side to the radial outer side.

[0016] As one of the preferred embodiments, the plurality of core columns also includes two core side columns, which are respectively disposed on the radial edges of the three core columns.

[0017] Compared with the prior art, this application has the following advantages: The converter transformer provided in this application, compared to traditional converter transformer structures, integrates three-phase, three-winding functions through a unified tank structure and bushing arrangement, effectively simplifying wiring structure and on-site construction, and improving system integrity and coordination. Adopting a three-phase, three-winding integrated structure, the converter transformer is led out horizontally from the tank on the valve side, making it more suitable for scenarios with height restrictions. This reduces the overall installation height of the transformer, significantly reducing the station layout area and effectively accommodating the connection and installation of increasingly smaller converter valve halls in the future. A single converter transformer achieves simultaneous three-phase commutation, reducing the workload of operation and maintenance. The previous multi-unit operation and maintenance has been reduced to a single unit, lowering maintenance risks and improving substation operation and maintenance efficiency. By placing the AC ABC three-phase windings, the valve-side Y winding, and the valve-side D winding in the same converter transformer, 12-pulse commutation can be achieved with only a single converter transformer, maximizing the reduction in the number of devices and significantly reducing the required bushings, voltage regulating devices, tanks, and other components, resulting in significantly optimized overall manufacturing, transportation, and installation costs. Attached Figure Description

[0018] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a three-dimensional structural diagram of a three-phase three-winding converter transformer applicable to a high-voltage direct current transmission system according to an embodiment of this application; Figure 2 This is an electrical wiring schematic diagram of a three-phase, three-winding converter transformer applicable to a high-voltage direct current transmission system according to an embodiment of this application; Figure 3 This is a cross-sectional view of the winding structure of a three-phase three-winding converter transformer suitable for a high-voltage direct current transmission system according to an embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 1. Transformer oil tank; 2. Grid-side bushing; 31. Valve Y-side bushing; 32. Valve D-side bushing; 4. Valve D-side winding; 5. Voltage regulating winding; 6. Grid-side winding; 7. Valve Y-side winding. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be noted that a single-phase dual-winding converter transformer consists of a primary winding connected to the AC system and a secondary winding connected to the converter. It emphasizes high performance and large capacity. Six single-phase dual-winding converter transformers, configured with six double-valve towers, achieve 12-pulse converter operation and are core equipment for UHVDC transmission. A single-phase three-winding converter transformer consists of a primary winding connected to the AC system and two secondary windings connected to two converters or different converter stages, respectively. It emphasizes economy and simplicity, and is suitable for small to medium capacity 6-pulse converter operation. This type of single-phase multi-unit combination is the most mature in engineering practice. Because a single-phase transformer uses at least three converter transformers to form a unit, according to fire protection requirements, firewalls and separate fire protection systems are needed between each transformer. This method requires the most equipment, is the largest in size, has the lowest integration, and has the highest construction and maintenance costs.

[0023] Each phase of a three-phase dual-winding converter transformer contains one primary winding and one secondary winding, totaling three phases. Two three-phase dual-winding converter transformers are connected in parallel and configured with a 12-pulse converter for high-capacity DC transmission. Although this improves upon the single-phase multi-unit combination mode in terms of the number of units, to meet the same multiple converter requirements, such as two sets of three-phase six-pulse converters, more units are still needed. The electrical connections, busbar layout, and protection configuration remain complex, and the overall size and system complexity are still high. The overall space requirements of the converter station are large, limiting the compactness of the station area. There is significant room for improvement in achieving the compact design goals of future DC transmission projects.

[0024] Furthermore, existing converter transformers inherently rely on the large space of the air-insulated valve hall, achieving 12-pulse commutation through the combination of multiple devices, and are not strongly constrained by the volume of the converter valve hall. Therefore, even if the equipment is large and complex in structure, it can be installed and maintained in the valve hall with sufficient operating space. For example, in electrical connections, increasing the electrical spacing between windings is sufficient to meet electrical isolation requirements. However, the volume of converter valve halls is trending towards compactness, making the traditional method of increasing spacing to meet electrical isolation no longer applicable. Traditional converter transformer structures struggle to achieve high-voltage insulation within compact spaces, failing to meet the installation requirements of future miniaturized and modular valve halls.

[0025] Currently, three-phase three-winding converter transformers remain only in the theoretical and exploratory stages, with limited engineering applications and no mature engineering practice structure yet established. Therefore, there is an urgent need to propose a more compact, functionally integrated, and economical solution for three-phase three-winding converter transformers. This solution would utilize a single three-phase three-winding converter transformer to achieve equivalent electrical performance to a combination of multiple single-phase transformers or at least two three-phase two-winding converter transformers, fundamentally solving the problems of low integration, large size, complex system construction, and high cost inherent in existing technologies.

[0026] Reference Figure 1 As shown, Figure 1 This is a schematic diagram illustrating the overall structure of a three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems, as shown in this utility model. Figure 1 As shown, this utility model provides a three-phase three-winding converter transformer suitable for high-voltage direct current transmission systems. The converter transformer includes: a transformer tank 1, which includes a winding structure immersed in oil, the winding structure including a grid-side outlet, a valve Y-side outlet, and a valve D-side outlet; a grid-side bushing 2 group, including three grid-side bushings 2 set on the top of the transformer tank 1, the grid-side bushings 2 being used to lead out the grid-side outlet; and a valve-side bushing group, including a valve Y-side bushing group and a valve D-side bushing group set on the side wall of the transformer tank 1, the valve Y-side bushing group being used to lead out the valve Y-side outlet, and the valve D-side bushing group being used to lead out the valve D-side outlet. The valve Y-side bushing group includes three valve Y-side bushings 31, and the valve D-side bushing group includes three valve D-side bushings 32. Each valve Y-side bushing 31 and each valve D-side bushing 32 are aligned one by one in the height direction of the transformer tank 1, and the three valve Y-side bushings 31 and the three valve D-side bushings 32 are respectively arranged at intervals in the height direction perpendicular to the transformer tank 1.

[0027] Specifically, this utility model embodiment is a three-phase, three-winding converter transformer for DC power transmission. It mainly achieves high performance, miniaturization, low cost, and engineering friendliness of the converter transformer equipment in the converter transformer system by technically modifying the tank structure, electrical wiring method, and winding structure arrangement strategy. This transforms the AC system voltage to the commutation voltage required by the connected converter. Therefore, other components of the converter transformer that are not detailed herein should be obtainable from known technologies, including but not limited to cooling devices, bushing structures, insulation support structures, pressure relief valves, gas relays, temperature and oil level monitoring devices, grounding and sampling accessories, etc. For clarity and brevity, these will not be elaborated upon further in this document.

[0028] Specifically, regarding the tank structure, transformer tank 1 is filled with insulating oil for insulation and cooling. To meet the AC / DC conversion requirements of the converter system, a three-winding structure was designed based on the electromagnetic relationships of the three-phase, three-winding system (multi-phase, multi-winding phase-to-phase coupling, DC bias model, harmonic loss model), engineering practices (insulation loss, protection mechanisms), and operating characteristics (short-circuit impedance, wiring method, voltage regulation range). Each phase's three-winding structure corresponds to the grid-side output, valve Y-side output, and valve D-side output. The grid-side output is used to connect to the external AC system, while the valve Y-side and valve D-side outputs are used to connect to the AC-side output of the converter. The three grid-side outputs of the converter transformer are located at the top of transformer tank 1 and are directly connected to the substation overhead line or high-voltage cable via high-voltage grid-side bushing 2. The six valve-side outputs of the converter transformer are arranged on any one of the four sides of transformer tank 1 and are led out via the corresponding valve-side bushings. Among them, the three valve Y-side outgoing lines and the three valve D-side outgoing lines each correspond to a set of three phases, which are led out through the three valve Y-side bushing 31 and the three valve D-side bushing 32 respectively, and combined with the external converter to realize 12-pulse commutation.

[0029] Therefore, in terms of grid-side layout, the top-entry method matches the insulation layout requirements of the high-voltage system. Simultaneously, the top-entry grid-side outgoing lines are structurally located away from the ground control cabinet and secondary systems, effectively reducing electromagnetic interference and improving the system's electrical safety. Combined with a lifting maintenance platform, the operation and maintenance process is simplified, and maintenance efficiency is improved. In terms of valve-side layout, the outgoing lines of the two sets of valve Y-side bushing groups and valve D-side bushing groups are respectively located on the side wall of transformer tank 1, using a side-outgoing method to connect to the rectifier valve group. The valve-side outgoing lines on the same side wall not only facilitate symmetrical arrangement of the converter transformer, shortening cable length and reducing wiring inductance, but also provide a suitable installation and maintenance height, improving the safety and efficiency of human-machine operation. The side-outgoing line structure can effectively cooperate with the compact converter system. This design can output DC voltage from ±50kV to ±500kV, meeting the high-efficiency, low-cost, and high-reliability requirements of the high-voltage DC transmission system for new energy transmission.

[0030] As a specific illustration of this embodiment, the valve Y-side bushings 31 and valve D-side bushings 32 corresponding to the output lines of the two secondary windings Y and D are aligned in the height direction of the oil tank, and the three valve Y-side bushings 31 or three valve D-side bushings 32 in the valve side bushing group can be spaced apart along the length or width direction of the transformer oil tank 1. Therefore, the valve Y-side bushing group and the valve D-side bushing group are arranged in two rows on the side wall of the transformer oil tank 1, with three valve side bushings in each row. The arrangement direction of the valve D-side bushings 32 is the same as the arrangement direction of the valve Y-side bushings 31. Each corresponding valve Y-side bushing 31 and valve D-side bushing 32 are arranged side by side, for example, the valve Y-side bushing 31 of phase A1 is arranged side by side below the valve Y-side bushing 31 of phase A2. For example, if the valve side bushing group is set on the left / right side wall of the transformer oil tank 1, the three valve Y-side bushings 31 are spaced apart along the width direction. If the valve side bushing assembly is installed on the front / rear side wall of the transformer tank 1, the three valve Y side bushings 31 are spaced apart along the length direction.

[0031] In some embodiments, in a double-row, three-column design, the corresponding valve Y-side sleeve 31 and valve D-side sleeve 32 in the same column can be staggered rather than side-by-side. In some embodiments, in a double-row, three-column design, the three valve Y-side sleeves 31 or the three valve D-side sleeves 32 in the same row can be arranged along a direction inclined to the length / width direction.

[0032] Preferably, when the transformer tank 1 is a rectangular enclosure, the valve-side bushing assembly is installed on the side wall along the length of the enclosure (i.e., the length-height enclosing surface), and the three valve Y-side bushings 31 are arranged along the length direction. This allows for full utilization of the installation space within the limited volume of the transformer tank 1. Correspondingly, the arrangement direction of the multiple grid-side bushings 2 is parallel to the arrangement direction of the multiple valve Y-side bushings 31; that is, the three grid-side bushings 2 are also arranged along the length direction on the top wall of the enclosure (i.e., the length-width enclosing surface). This maximizes the utilization of the enclosure wall's installation space and allows for the design of appropriate electrical spacing.

[0033] Preferably, the high losses of a three-phase, three-winding converter transformer, due to the superposition of copper losses in the three windings, additional losses caused by commutation harmonics, and increased iron losses from DC bias, result in significantly higher heat dissipation requirements compared to traditional converter transformer structures. Traditional single-mode heat dissipation is insufficient to meet these requirements. This embodiment incorporates a cooling mechanism, including a natural circulation cooling structure and a forced circulation cooling structure. The natural circulation cooling structure is located inside the transformer tank 1, for example, using guide oil channels to guide the transformer oil through temperature fluctuations within the tank, achieving natural oil circulation cooling. The forced circulation cooling structure is located outside the transformer tank 1, for example, using a combination of an oil pump and a radiator. The radiator pumps the cooled transformer oil back into the tank 1 to cool the heat-generating components (mainly the winding structure), and then the heated oil flows back to the radiator, achieving forced oil circulation cooling. Therefore, this dual heat dissipation mode satisfies the higher heat dissipation requirements of the three-phase, three-winding converter transformer.

[0034] Therefore, compared with the traditional structure of converter transformers, the embodiments of this utility model have at least the following advantages: 1. Due to the need for high insulation levels (to cope with commutation overvoltage and DC components), strong heat dissipation capacity (due to high harmonic losses), and special winding structures (such as winding shielding layers and complex wiring), traditional transformer tanks have larger volumes and core diameters than conventional transformers. This utility model embodiment integrates three-phase, three-winding functions by unifying the tank structure and bushing arrangement, effectively simplifying the wiring structure and on-site construction, and improving the overall system integrity and coordination.

[0035] 2. Traditional converter transformers inherently rely on the large space conditions of air-insulated valve halls, and the electrical spacing is not limited by volume. This utility model embodiment adopts a three-phase, three-winding integrated structure, with the converter transformer led out horizontally from the oil tank on the valve side. This is more suitable for scenarios with height restrictions, reducing the overall installation height of the transformer and significantly reducing the site layout area. It can effectively accommodate the connection and installation of converter valve halls that are becoming increasingly smaller in the future.

[0036] 3. Single-phase converter transformers can only meet the single-phase conversion function. If three-phase simultaneous conversion is required, a three-phase system consisting of three single-phase transformers per pole is needed. When multiple devices are arranged in parallel to meet the three-phase requirements, it leads to complex wiring, numerous outgoing lines, and lengthy signal and power transmission paths, increasing the assembly, debugging, operation, and maintenance costs of the system. In this embodiment, a single converter transformer achieves three-phase simultaneous conversion, reducing the workload of operation and maintenance. The number of units required for maintenance has been reduced from 6 / 3 / 2 to a single unit, thus reducing the risk of operation and maintenance and improving the efficiency of substation operation and maintenance.

[0037] 4. The converter transformer needs to withstand mixed AC / DC voltage, commutation overvoltage, and DC bias, therefore the winding insulation (paper, oil, barrier) requires special design; the harmonics generated by the converter will cause additional transformer losses (copper losses and iron losses increase by 10%-20%), which need to be offset by special design; the winding, insulation assembly, and overall drying processes require extremely high precision; in a 12-pulse converter system, the total cost of connecting 6 single-phase double-winding converter transformers / 3 single-phase three-winding converter transformers / 2 three-phase double-winding converter transformers is too expensive, requiring more bushings, tap changers, and matching transformer tanks, significantly increasing the total system investment. This utility model embodiment places the AC ABC three-phase windings, valve-side Y winding, and valve-side D winding in the same converter transformer, achieving 12-pulse converter with only a single converter transformer, greatly reducing the number of equipment, the required bushings, voltage regulating devices, tanks, and other components, and significantly optimizing the overall manufacturing, transportation, and installation costs.

[0038] It is worth mentioning that, in this embodiment of the utility model, the six valve-side bushings in the valve-side bushing assembly can also be arranged in a single row of six columns, three rows of double columns, or six rows of single columns on the side wall of the transformer tank 1, integrating the Y-connected and Δ-connected valve-side windings into one unit, and completing 12-pulse commutation with a single unit. Compared with the traditional structure of the converter transformer, this can still be considered an optimized solution, resulting in a smaller footprint, fewer bushings, and the highest system integration. In actual design, the arrangement of the valve-side bushings of the converter transformer directly affects the safety, reliability, and economy of the equipment. This embodiment is based on multiple dimensions of design goals, including space optimization, mechanical strength, converter valve connection, insulation performance, balancing cost, and engineering implementation difficulty. Through dedicated simulation tools, it optimizes from scratch and designs a double-row parallel arrangement, achieving multiple goals.

[0039] Specifically, in the actual implementation process: In terms of mechanical strength: Transformer tank 1 has a box-type structure with vertical plane structures on its sides (side walls). It primarily bears the radial load (horizontal outward force generated by its own weight) and short-circuit electrodynamic force (horizontal impact force) of the bushings. Its stress logic differs from that of the top (which primarily bears vertical loads). This embodiment uses this design to distribute the radial load across two height ranges of the side walls, reducing the load per row by 50%. Therefore, two rows of support structures can be installed on the inner side wall of transformer tank 1, with the support structures and valve-side bushing assemblies located on the same side wall of transformer tank 1. The two rows of support structures are spaced apart along the height direction of transformer tank 1, with the valve Y-side bushing assembly fixed to the upper side wall of transformer tank 1 via the upper row of support structures, and the valve D-side bushing assembly fixed to the lower side wall of transformer tank 1 via the lower row of support structures. This adapts to the stress characteristics of the side walls and reduces the risk of deformation. Thus, the support structures (such as reinforcing ribs) can be arranged in a distributed manner (each row of bushings corresponds to an independent small reinforcing frame), resulting in a more uniform stress distribution in the overall structure.

[0040] For example, please refer again Figure 1 Two rows of valve Y-side bushings and valve D-side bushings extend outward from the right side wall of transformer tank 1, and corresponding upper and lower rows of support structures are set on the inner side of the right side wall of transformer tank 1.

[0041] Regarding the connection with external converters: Converter valves are typically located on the side of the converter transformer (on the same side as the bushing), stacked vertically in a "tower" shape (height can reach 10m-20m). The connection between the valve-side bushing and the converter valve is mainly via horizontal rigid busbars (copper busbars or aluminum tubes), and the path length and orientation directly affect electrical performance. This embodiment, through this design, directly corresponds to the layered structure of the converter valves (the upper row of valve-side bushings connects to the upper-level modules in the valve tower, and the lower row of converter bushings connects to the lower-middle modules), shortening the busbar path to 2-3 meters (straight horizontal connection), controlling stray inductance within 10-15μH, and reducing overvoltage amplitude by 20%-30%. Furthermore, the shorter busbars offer better rigidity, eliminating the need for intermediate supports and reducing electric field distortion points; simultaneously, the thermal expansion and contraction of the horizontal busbars can be easily compensated for by end expansion joints (single-row long busbars require multi-stage compensation), resulting in higher connection reliability.

[0042] Regarding transportation: The transportation of converter transformers must meet width, height, and weight restrictions. The arrangement of the side bushings directly affects the equipment's "outline dimensions" and weight distribution. This embodiment utilizes a design where the double-row valve-side bushings are staggered in the height direction, with the lateral protrusion width determined only by the diameter of a single valve-side bushing (0.8-1.2 meters). This eliminates the need to exceed transportation width restrictions, enabling "integrated transportation" (pre-installed bushings) and saving on-site installation time. Simultaneously, the distributed load distribution between the upper and lower rows makes the tank's center of gravity more central, resulting in more even stress distribution on the vehicle during transportation and reducing the risk of overturning. Furthermore, the distributed support structure (such as independent upper and lower row reinforcing frames) is 8%-12% lighter than a single-row / single-column concentrated "heavyweight frame," making it easier to meet weight restrictions.

[0043] Regarding insulation: Side-mounted valve bushings are directly exposed to the external environment (rain, snow, dust, dirt), and their electric field distribution is affected by the three-dimensional space of "sidewall-bushing-air," making the arrangement more significant to insulation reliability. This embodiment utilizes this design to effectively increase the phase-to-phase distance between the upper and lower rows, reducing electric field coupling. The root field strength can be reduced to 25-30 kV / cm (no need for ultra-large grading rings; a diameter of 1.5m-2m is sufficient). The upper row of valve bushings provides some shielding to the lower row, reducing direct rainwater erosion of the lower row's surface. Furthermore, the difference in dirt accumulation rates between the upper and lower rows (the upper layer accumulates dirt more easily, while the lower layer accumulates less due to shielding) reduces the overall probability of dirt flashover. Since the angle of sunlight on the side (such as direct sunlight at midday in summer) can cause the bushing temperature to rise, the vertical spacing between the upper and lower rows increases air convection space, reducing local temperature rise (measured temperature difference can reach 5-8℃), and preventing high temperatures from accelerating insulation aging.

[0044] In terms of cost: the cost of side bushing arrangement needs to be evaluated in conjunction with the entire process of "manufacturing-transportation-operation and maintenance". The advantage of double-row arrangement is reflected in long-term economic efficiency. In this embodiment, this design eliminates the need for detachable structures (saving on sealing costs). Therefore, the grid-side bushing 2, valve Y-side bushing group, and valve D-side bushing group are all fixed to the transformer tank 1. Distributed support results in lower material consumption (reduced by 8%-12%); overall transportation eliminates on-site disassembly and assembly costs; improved insulation reliability extends the operation and maintenance cycle (from 3 years to 5 years), and the total life cycle cost can be reduced by 15%-20%.

[0045] To balance these multi-dimensional advantages, the specific structural design of transformer tank 1 includes a height of 12.6m, a length of 7.5m, and a width of 5.9m. The spacing between adjacent valve Y-side bushings 31 is greater than 1.5m; the spacing between each pair of vertically aligned valve Y-side bushings 31 and valve D-side bushings 32 is 1.5m-2m. Furthermore, this design avoids problems such as insulation failure due to excessively small horizontal spacing between bushings in the same row, creepage and flashover due to insufficient vertical spacing between bushings in the same column, and excessive stress, structural damage, insufficient maintenance space, and accelerated contamination accumulation caused by excessively small bushing spacing in the same row and column. It also avoids situations where excessively large horizontal and / or vertical spacing exceeds the installation space of transformer tank 1, preventing further reduction in the converter system volume.

[0046] In summary, compared to single-row centralized arrangement, which is only suitable for low-voltage, small-capacity scenarios due to transportation limitations, concentrated stress, and insulation risks, and three-row two-by-two arrangement increases the tank height (potentially exceeding transportation height limits), and the connection path of the middle row bushings is complex, resulting in very few engineering applications. The three-phase three-winding converter transformer structure provided in this embodiment has advantages in multiple dimensions, including space optimization, mechanical strength, converter valve connection, insulation performance, balancing cost, and engineering implementation difficulty, and can adapt to converter station scenarios with limited space.

[0047] A further improvement of this invention is that each grid-side bushing 2 extends vertically from the top of the transformer tank 1, while each valve Y-side bushing 31 and each valve D-side bushing 32 extends horizontally from the side wall of the transformer tank 1. Therefore, in this embodiment, the grid-side bushing 2 is a vertical bushing, and the valve-side bushing is a horizontal bushing. The top exit of the grid-side bushing can adapt to the vertical space configuration requirements of the ultra-high voltage bushings, allowing the high-voltage leads to connect to the external system via the shortest path and reducing the risk of electric field concentration in the leads. All six valve-side bushings are horizontal and side-by-side from the same side wall of the transformer tank 1, allowing for the most compact interface and achieving the shortest connection path.

[0048] As a preferred implementation method, such as Figure 2 As shown, Figure 2This is an electrical wiring diagram of a three-phase, three-winding converter transformer according to an embodiment of this application. In terms of converter circuit topology, the three-winding structure adopts a YY / D structure. The valve-side outputs are divided into upper and lower groups, corresponding to the input terminals of two groups of six-pulse converter valves with Y-connection and Δ-connection, respectively. Three valve Y-side outputs (A1, B1, C1) are connected in a Y-connection to the input terminal of the first group of three-phase six-pulse converter valves, and three valve D-side outputs (e.g., A2, B2, C2) are connected in a Δ-connection to the input terminal of the second group of three-phase six-pulse converter valves. A single converter transformer achieves the output of two groups of valve-side windings. The first group is star (Y) connected, and the second group is delta (Δ) connected, thus generating a 30° phase difference, supplying power to the two groups of three-phase six-pulse converter bridges respectively, meeting the requirements of 12-pulse converter. Because the valve-side winding of the converter transformer needs to eliminate the third harmonic generated by commutation through special wiring (to avoid grid-side pollution), it must be strictly matched with the symmetry of the three-phase system. The valve-side winding adopts a Δ connection to ensure that the three-phase phase difference is strictly 120°. Therefore, the wiring method in this embodiment effectively reduces the harmonic content of the 6-pulse rectification, making the DC system operation more reliable, greatly simplifying the filter system design, and reducing the investment cost of the converter station.

[0049] As a preferred implementation method, such as Figure 3 As shown, Figure 3 This is a cross-sectional view of the winding structure of a three-phase, three-winding converter transformer according to an embodiment of this application. Regarding the winding structure, the winding structure includes multiple core columns and three-phase windings; the multiple core columns include three main core columns, each with a corresponding phase winding wound on it. Each phase winding includes a grid-side winding 6, a voltage regulating winding 5, a valve Y-side winding 7, and a valve D-side winding 4; wherein, in the radial direction of the core columns, the grid-side winding 6 is located between the valve Y-side winding 7 and the valve D-side winding 4. Further, the multiple core columns also include two side core columns, which are respectively disposed at the radial edges of the three core columns.

[0050] In this embodiment, a five-column core design is adopted, with three main columns and two side columns. Three main yokes are wound around each phase winding. Each phase valve Y-side winding 7 corresponds to a corresponding valve Y-side lead-out, and each phase valve D-side winding 4 corresponds to a corresponding valve D-side lead-out. Two side yokes are used for flux closure. The voltage regulating winding 5 needs to compensate for grid-side voltage fluctuations (e.g., within ±10%) in real time to ensure stable valve-side commutation voltage. The voltage regulation speed of the three-phase, three-winding converter transformer can complete ±1% adjustment within 200ms. Its voltage regulation speed and range are optimized through co-simulation based on the control algorithm of the external converter valve.

[0051] The insulation distance of each phase winding in the oil is calculated using equation (1): Equation (1) Wherein, U_resistance is the peak withstand voltage in kV; E_oil is the allowable electric field strength of the transformer oil in kV / mm; and K_oil is a correction factor that takes into account oil flow and impurities.

[0052] Among them, E oil has a value of 3kV / mm-5kV / mm, which is the upper limit of clean oil; K oil is a constant with a value of 1.05~1.2.

[0053] The main insulation distance between each phase winding needs to take into account the voltage gradient distribution (axial and radial). The winding structure of this patent is cylindrical, and the axial voltage level remains unchanged. Only the change in radial voltage level is considered in the calculation. Therefore, the calculation formula is combined with the winding voltage difference and solved by equation (2): Equation (2) Among them, U 差 G represents the voltage difference between the two windings, expressed in kV. 径向 This represents the maximum permissible radial voltage gradient, expressed in kV / mm.

[0054] Among them, U 差 The value is the difference between the highest operating voltage and the overvoltage; G 径向 The value is determined by the insulating material and structure, and ranges from 1kV / mm to 2kV / mm.

[0055] Three-phase, three-winding converter transformers require the simultaneous design of three sets of short-circuit impedances: "grid-side - valve-side," "grid-side - voltage regulator," and "valve-side - voltage regulator." The impedance design depends on the radial / axial arrangement of the windings, the leakage flux shielding structure, and must consider the magnetic circuit coupling of the three-phase cores (zero-sequence leakage flux caused by commutation asymmetry). Therefore, this embodiment designs a winding arrangement for the three-phase, three-winding converter transformer, which optimizes the insulation of the two valve-side windings. Grid-side winding 6, as an intermediate layer, forms a magnetic barrier and mechanical buffer against high-frequency harmonics and short-circuit impacts, significantly reducing valve-side harmonic interference and winding mechanical stress.

[0056] In some embodiments, the arrangement includes a valve D-side winding 4, a mesh-side winding 6, a voltage regulating winding 5, and a valve Y-side winding 7; a valve D-side winding 4, a mesh-side winding 6, a valve Y-side winding 7, and a voltage regulating winding 5; a voltage regulating winding 5, a valve D-side winding 4, a mesh-side winding 6, and a valve Y-side winding 7; a valve D-side winding 4, a voltage regulating winding 5, a mesh-side winding 6, and a valve Y-side winding 7, or other forms. By placing the mesh-side winding 6, which has higher losses, in the middle, heat can be conducted bidirectionally to the valve-side windings, improving cooling efficiency.

[0057] Preferably, the windings of each phase, from the inside out, are: valve Y-side winding 7, grid-side winding 6, voltage regulating winding 5, and valve D-side winding 4. This arrangement considers both heat dissipation balance and insulation coordination, and rationally distributes the internal windings. It employs a winding structure with an internal valve-side Y-side winding 7, a centrally located AC winding 6, and an externally located valve-side D-side winding 4, achieving effective electromagnetic shielding and mechanical balance within the five-limb core. In particular, the AC winding acts as a magnetic barrier layer, significantly reducing electromagnetic interference between the valve-side windings. The symmetrical arrangement also facilitates self-balancing of axial and radial forces, improving short-circuit withstand capability and mechanical stability. In terms of manufacturing and maintenance, the standardized winding structure reduces manufacturing errors and the complexity of spare parts management, offering significant advantages in engineering implementation.

[0058] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0059] It should also be noted that, in this document, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations, nor should they be construed as indicating or implying relative importance. Moreover, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device.

Claims

1. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems, characterized in that, Converter transformers include: The transformer tank includes a winding structure immersed in oil, the winding structure including a grid-side outlet, a valve Y-side outlet, and a valve D-side outlet; Cooling mechanisms include natural circulation cooling structures and forced circulation cooling structures; The grid-side bushing assembly includes three grid-side bushings installed on the top of the transformer tank, which are used to lead out the grid-side outgoing lines. The valve side bushing assembly includes a valve Y side bushing assembly and a valve D side bushing assembly disposed on the side wall of the transformer tank. The valve Y side bushing assembly is used to lead out the valve Y side outlet line, and the valve D side bushing assembly is used to lead out the valve D side outlet line. The valve Y-side bushing group includes three valve Y-side bushings, and the valve D-side bushing group includes three valve D-side bushings; each valve Y-side bushing and each valve D-side bushing are aligned one-to-one in the height direction of the transformer tank, and the three valve Y-side bushings and the three valve D-side bushings are respectively spaced apart in the height direction perpendicular to the transformer tank.

2. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 1, characterized in that, The winding structure includes five iron core columns and a three-phase winding; The five core columns include three core main columns, and each core main column is wound with a corresponding phase winding, which includes a grid-side winding, a voltage regulating winding, a valve Y-side winding, and a valve D-side winding. In the radial direction of the core column, the mesh-side winding is located between the valve Y-side winding and the valve D-side winding.

3. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 1, characterized in that, Each of the grid-side bushings extends vertically from the top of the transformer tank, and each of the valve Y-side bushings and each of the valve D-side bushings extends horizontally from the side wall of the transformer tank.

4. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 1, characterized in that, The arrangement direction of the multiple mesh-side sleeves is parallel to the arrangement direction of the multiple valve Y-side sleeves.

5. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 1, characterized in that, The valve Y-side output line is connected to the input terminal of the first group of three-phase six-pulse converter valves using a Y-connection method, and the valve D-side output line is connected to the input terminal of the second group of three-phase six-pulse converter valves using a Δ-connection method.

6. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to any one of claims 1-5, characterized in that, The transformer tank has a height of 12.6m, a length of 7.5m, and a width of 5.9m; the spacing between two adjacent valve Y-side bushings is greater than 1.5m; the spacing between each pair of valve Y-side bushings and valve D-side bushings is 1.5m-2m.

7. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 6, characterized in that, The grid-side bushing, the valve Y-side bushing assembly, and the valve D-side bushing assembly are all fixed to the transformer tank.

8. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 1, characterized in that, The inner side of the target sidewall of the transformer tank is provided with two rows of support structures, and the target sidewall is the sidewall of the transformer tank where the valve side bushing assembly is located. The two rows of support structures are spaced apart along the height direction of the transformer tank, and the valve Y-side bushing assembly is fixed to the upper side wall of the transformer tank through the upper row of support structures, while the valve D-side bushing assembly is fixed to the lower side wall of the transformer tank through the lower row of support structures.

9. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 2, characterized in that, Each of the iron core main columns is wound sequentially from the radial inside to the radial outside with a valve Y-side winding, a mesh-side winding, a voltage regulating winding, and a valve D-side winding.

10. A three-phase, three-winding converter transformer suitable for high-voltage direct current transmission systems according to claim 2, characterized in that, The plurality of core posts also include two core side posts, which are respectively disposed on the radial edges of the three core posts.

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