Parallel-connected converter transformer for extra-high voltage flexible direct current transmission

Abstract

The present application relates to a kind of parallel converter transformers for extra-high voltage flexible AC transmission, wherein valve a parallel channel inlet end is fixed on the first oil tank, outlet end is fixed on the second oil tank, valve b parallel channel inlet end is fixed on the second oil tank, outlet end is fixed on the first oil tank, the first valve a outlet pipe of first body group is connected with valve a parallel channel inlet end, the first valve b outlet pipe is merged with valve b parallel lead-out pipe from valve b parallel channel outlet end, the second valve a outlet pipe of second body group is merged with valve a parallel lead-out pipe from valve a parallel channel outlet end, the second valve b outlet pipe is connected with valve b parallel channel inlet end, the middle part of two parallel channels is equipped with adjusting bellow, and adjusting bellow is equipped with intermediate outlet device inside.The single body structure of existing converter transformer is changed to double body parallel structure in the present application, which can effectively avoid winding temperature rise and magnetic flux leakage overheating and other problems, and also meet transportation requirements.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, specifically to a parallel converter transformer for ultra-high voltage flexible DC transmission. Background Technology

[0002] Converter transformers, as a crucial component of UHVDC converter stations, are core equipment responsible for AC / DC conversion. The development of UHVDC technology has spurred a shift towards larger capacity converter transformers. Traditional DC projects typically employ a dual-twelve-pulse design, resulting in a single converter transformer capacity of approximately 400 MVA for an 8 GW DC project. However, UHVDC technology utilizes a symmetrical bipolar structure, requiring only half the number of converter transformers compared to traditional DC transmission. Even with an 8 GW UHVDC project, the capacity of a single converter transformer would increase to over 750 MVA. This represents a 25% increase in converter transformer capacity compared to the current largest capacity (607.5 MVA) and an 80% increase compared to the conventional 8 GW capacity (415 MVA). However, this significant capacity increase, while bringing positive effects such as enhanced transmission capacity, inevitably raises a series of technical challenges, including:

[0003] I. From a thermal performance perspective, increasing capacity will increase the electrical density in the transformer windings and also increase the radial direction of the windings. This will significantly increase the temperature rise of the windings. For example, the copper-oil temperature difference of the previously designed converter transformer was only 25K, but if it meets the requirements of railway transportation, the copper-oil temperature difference of the converter transformer after capacity increase will increase to 30-40K or even higher. This will cause the temperature rise of the winding hot spots to exceed 115℃. Excessive temperature not only accelerates the aging process of the insulation material and reduces the insulation performance, but may also cause serious faults such as insulation breakdown, affecting the long-term stable operation of the transformer.

[0004] Second, as the capacity of the converter transformer increases, the leakage flux at the winding ends will increase significantly. When the leakage flux passes through the clamps and oil tank, it will cause partial discharge and overheating of the metal parts. The local high temperature overheating will cause carbonization and gas generation of the insulation parts or transformer oil, which will further threaten the reliability and safety of the equipment.

[0005] Third, in terms of transportation, converter transformers are usually transported by rail or road, and there are restrictions on transportation conditions. For example, the dimensions for rail transport are 13×3.5×4.85 (meters), and the transport weight is only 350 tons. However, a conventional 400MVA converter transformer has already reached the upper limit of rail transport. The transport weight of a converter transformer with increased capacity (750MVA, ±800kV) further reaches more than 450 tons, which can no longer meet the transportation requirements of rail and road. If a single large-capacity converter transformer is designed and transported by rail or road, it is necessary to carry out engineering such as road and bridge construction and tunnel expansion. This will greatly increase the complexity of project implementation and transportation costs, making normal transportation impossible. Summary of the Invention

[0006] The purpose of this invention is to provide a parallel converter transformer for ultra-high voltage flexible DC transmission, which changes the existing single-body structure of converter transformers to a double-body parallel structure, which can effectively avoid problems such as winding temperature rise and leakage flux overheating, while also meeting transportation requirements.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A parallel converter transformer for ultra-high voltage flexible DC transmission includes a first oil tank, a second oil tank, a parallel channel for valve a, and a parallel channel for valve b. The inlet end of the parallel channel for valve a is fixed to the first oil tank, and the outlet end is fixed to the second oil tank. The inlet end of the parallel channel for valve b is fixed to the second oil tank, and the outlet end is fixed to the first oil tank. A first transformer body assembly is housed in the first oil tank, and a second transformer body assembly is housed in the second oil tank. The first valve a outlet pipe on the first transformer body assembly is connected to the inlet end of the parallel channel for valve a. The second valve a outlet pipe on the second transformer body assembly merges with the parallel outlet pipe for valve a extending from the outlet end of the parallel channel for valve a to form a combined outlet pipe for valve a. The outlet pipe of the second valve b on the main body assembly is connected to the inlet end of the parallel channel of valve b. The outlet pipe of the first valve b on the first main body assembly and the parallel outlet pipe of valve b led out from the outlet end of the parallel channel of valve b merge to form the valve b main outlet pipe. The middle of the parallel channel of valve a and the middle of the parallel channel of valve b are provided with adjusting bellows, and the adjusting bellows are provided with lifting seats on both sides and an intermediate outlet device inside. The intermediate outlet device includes a first shielding cylinder and a first cardboard corrugated cylinder arranged sequentially from the outside to the inside. The first cardboard corrugated cylinder is provided with an intermediate equalizing ball connecting the two pipelines inside. One end of the first shielding cylinder is fixed on the lifting seat on the corresponding side, and the other end is provided with a limiting insulating screw.

[0009] A first fixing clamp is provided between the first shielding cylinder and the first cardboard corrugated cylinder, and pressure equalization pipes are provided at both ends of the first shielding cylinder.

[0010] The first shielding cylinder has a cardboard ring at its end, and the cardboard ring has threaded holes evenly distributed around its circumference. Paper-based limiting and insulating screws are installed in the corresponding threaded holes.

[0011] The parallel channel of valve a includes a first valve a outlet device, a valve a intermediate outlet device, and a second valve a outlet device connected sequentially through a valve a connecting pipe. The first valve a outlet device is fixed to the first oil tank, and the second valve a outlet device is fixed to the second oil tank. The parallel channel of valve b includes a first valve b outlet device, a valve b intermediate outlet device, and a second valve b outlet device connected sequentially through a valve b connecting pipe. The first valve b outlet device is fixed to the second oil tank, and the second valve b outlet device is fixed to the first oil tank. The first valve a outlet pipe is connected to the first valve a outlet device. The second valve a outlet pipe merges with the parallel outlet pipe of valve a led out from the second valve a outlet device. The second valve b outlet pipe is connected to the first valve b outlet device, and the first valve b outlet pipe merges with the parallel outlet pipe of valve b led out from the second valve b outlet device.

[0012] The first valve a outlet device, the second valve a outlet device, the first valve b outlet device, and the second valve b outlet device have the same structure. They all include a second shielding cylinder, a second fixing clamp, and a second cardboard corrugated cylinder arranged sequentially from the outside to the inside. The second cardboard corrugated cylinder has an end equalizing ball that connects the pipes on both sides inside.

[0013] The parallel channel of valve a includes a first valve a riser seat, a valve a regulating bellows, and a second valve a riser seat connected in sequence. The valve a regulating bellows is provided with a valve a middle outlet device. The outer end of the first valve a riser seat is fixedly connected to the first oil tank, and the outer end of the second valve a riser seat is fixedly connected to the second oil tank. A first housing shielding tube is provided on the outer side of the outer end of both the first and second valve a riser seats. One end of the first valve a outlet device is inserted into the first valve a riser seat, and one end of the second valve a outlet device is inserted into the second valve a riser seat.

[0014] The parallel channel of valve b includes a first valve b riser seat, a valve b regulating bellows, and a second valve b riser seat connected in sequence. The valve b regulating bellows is provided with a valve b intermediate outlet device. The outer end of the first valve b riser seat is fixedly connected to the second oil tank, and the outer end of the second valve b riser seat is fixedly connected to the first oil tank. A second housing shielding tube is provided on the outer side of the outer end of both the first and second valve b riser seats. One end of the first valve b outlet device is inserted into the first valve b riser seat, and one end of the second valve b outlet device is inserted into the second valve b riser seat.

[0015] The parallel channel of valve a is located on the upper side between the first oil tank and the second oil tank, and the parallel channel of valve b is located at the bottom between the first oil tank and the second oil tank.

[0016] The first oil tank is equipped with a valve b sleeve, a first oil reservoir, a first mesh side sleeve, and a first mesh side neutral point sleeve. The second oil tank is equipped with a valve a sleeve, a second oil reservoir, a second mesh side sleeve, and a second mesh side neutral point sleeve. The valve a collection outlet pipe is connected to the valve a sleeve, and the valve b collection outlet pipe is connected to the valve b sleeve.

[0017] Both the parallel channel of valve a and the parallel channel of valve b are equipped with oil-blocking baffles to block the oil flow between the first oil tank and the second oil tank.

[0018] The advantages and positive effects of this invention are as follows:

[0019] 1. This invention changes the single-body structure of the upgraded converter transformer (750MVA, ±800kV) to a double-body parallel structure. This reduces the capacity of each tank body unit to approximately 375MVA to 400MVA, effectively avoiding problems such as winding temperature rise and leakage flux overheating. At the same time, the volume and weight of a single tank body unit can meet transportation requirements. Furthermore, this invention only adds two lead connection channels, valve a parallel channel and valve b parallel channel, without increasing design complexity or the number of valve-side bushings, thus saving costs.

[0020] 2. The invention incorporates regulating bellows in the middle of both the parallel channels of valve a and valve b for adjustment, facilitating on-site installation and reducing the requirements for the flatness of the foundation. Considering the presence of sharp corners, burrs, and other uneven electrodes on the internal surface of the regulating bellows, which can easily cause discharge, the invention includes a central lead-out device inside both bellows to avoid the influence of electric field distortion within the bellows and ensure insulation margin. During production, the parallel channels 3 (valve a) and 4 (valve b) of this invention must withstand a 900kV AC withstand voltage test for over 1 hour, a DC withstand voltage test of over 1200kV for over 2 hours, and a polarity reversal withstand voltage test of over 1000kV for over 1.5 hours.

[0021] 3. This invention facilitates the disassembly and separate transportation of the two tank body units, thus meeting transportation requirements. When disassembling the two tank body units, it is only necessary to disassemble the adjusting bellows from the riser on either side, and then separate the connecting pipe from the intermediate equalizing ball. In addition, the parallel structure of this invention does not increase the on-site assembly work too much, and there is no need to build an assembly plant or an additional test hall on-site, saving on-site installation costs.

[0022] 4. The parallel channel of valve a and the parallel channel of valve b of the present invention can be equipped with oil blocking baffles as needed to block the oil connection between the first oil tank and the second oil tank. In this way, when a fault is found in one oil tank body unit, it will not affect the operation of the other oil tank body unit, nor will it increase the difficulty of fault diagnosis. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 This is a schematic diagram showing the connections of the various parts of the present invention.

[0025] Figure 3 for Figure 1 A schematic diagram of the parallel channel of valve a.

[0026] Figure 4 for Figure 3 A schematic diagram showing the connections of the various components inside the parallel channel of valve a.

[0027] Figure 5 for Figure 4 Cross-sectional view of the internal components of the parallel channel of valve a.

[0028] Figure 6 for Figure 1 Schematic diagram of the parallel channel of valve b.

[0029] Figure 7 for Figure 6 A schematic diagram showing the connections of the various components inside the parallel channel of valve b.

[0030] Figure 8 for Figure 7 Cross-sectional view of the internal components of the parallel channel of valve b.

[0031] Figure 9 for Figure 8 Cross-sectional view of the intermediate outlet device of valve b.

[0032] Figure 10 for Figure 9 Enlarged view of point A in the image.

[0033] Figure 11 This is a schematic diagram of the electrical connection relationship of the present invention.

[0034] Wherein, 1 is the first oil tank, 101 is the valve b sleeve, 102 is the first oil storage tank, 103 is the first network side sleeve, 104 is the first network side neutral point sleeve, 105 is the first vessel body assembly, 106 is the first valve b outlet pipe, 107 is the valve b collection outlet pipe, and 108 is the first valve a outlet pipe; 2 is the second oil tank, 201 is the valve a sleeve, 202 is the second oil storage tank, 203 is the second network side sleeve, 204 is the second network side neutral point sleeve, 205 is the second vessel body assembly, 206 is the second valve b outlet pipe, 207 is the valve a collection outlet pipe, 208 is the second valve a outlet pipe; 3 is the valve a parallel channel, 301 is the valve a regulating bellows, 302 is the first valve a riser seat, 303 is the second valve a riser seat, 304 is the first valve a outlet device, and 305 is the second valve a outlet device. 306 is the first housing shielding tube, 307 is the intermediate outlet device of valve a, 308 is the valve a connecting pipe, 309 is the parallel outlet pipe of valve a, 4 is the parallel channel of valve b, 401 is the regulating bellows of valve b, 402 is the first valve b riser seat, 403 is the second valve b riser seat, 404 is the first valve b outlet device, 405 is the second valve b outlet device, 406 is the second housing shielding tube, 407 is the intermediate outlet device of valve b, 408 is the valve b connecting pipe, 409 is the parallel outlet pipe of valve b, 5 is the cooler, 6 is the end equalizing ball, 7 is the first cardboard corrugated cylinder, 8 is the first shielding cylinder, 9 is the first fixing clamp, 10 is the equalizing pipe, 11 is the second shielding cylinder, 12 is the second fixing clamp, 13 is the second cardboard corrugated cylinder, 14 is the intermediate equalizing ball, 15 is the fixing plate, and 16 is the limiting insulating screw. Detailed Implementation

[0035] The invention will now be described in further detail with reference to the accompanying drawings.

[0036] like Figures 1-11 As shown, the present invention includes a first oil tank 1, a second oil tank 2, a parallel channel 3 for valve a, and a parallel channel 4 for valve b, wherein... Figure 2 As shown, the inlet end of the parallel channel 3 of valve a is fixed to the first oil tank 1, and the outlet end is fixed to the second oil tank 2. The inlet end of the parallel channel 4 of valve b is fixed to the second oil tank 2, and the outlet end is fixed to the first oil tank 1. The first oil tank 1 is equipped with a first device body assembly 105, and the second oil tank 2 is equipped with a second device body assembly 205. The outlet pipe 108 of the first valve a on the first device body assembly 105 is connected to the inlet end of the parallel channel 3 of valve a. The outlet pipe 208 of the second valve a on group 205 merges with the parallel outlet pipe 309 of valve a led out from the outlet end of the parallel channel 3 of valve a to form the valve a general outlet pipe 207. The outlet pipe 206 of the second valve b on the second body group 205 is connected to the inlet end of the parallel channel 4 of valve b. The outlet pipe 106 of the first valve b on the first body group 105 merges with the parallel outlet pipe 409 of valve b led out from the outlet end of the parallel channel 4 of valve b to form the valve b general outlet pipe 107. Figures 3-8 As shown, both the middle of the parallel channel 3 of valve a and the middle of the parallel channel 4 of valve b are provided with adjusting bellows, and both adjusting bellows are provided with intermediate cable outlet devices inside. Figures 9-10 As shown, the intermediate cable exit device includes a first shielding cylinder 8 and a first corrugated cardboard cylinder 7 arranged sequentially from the outside to the inside. The first corrugated cardboard cylinder 7 has an intermediate equalizing ball 14 connecting the pipes on both sides inside. The adjusting corrugated pipe has lifting seats on both sides, and as shown... Figure 4 and Figure 7 As shown, the first shielding cylinder 8 has a fixing plate 15 fixed to the end of the corresponding side of the lifting seat at one end, and a limiting insulating screw 16 along the circumferential direction at the other end.

[0037] This invention addresses the field of ultra-high voltage flexible DC transmission, particularly considering that the converter transformer capacity of the new flexible DC system (750MVA, ±800kV) is more than 25% higher than the current largest capacity (607.5MVA) single-phase converter transformer, and more than 80% higher than the 8GW conventional capacity (415MVA) converter transformer. If a single large-capacity converter transformer design is adopted, problems such as significantly increased winding temperature rise, significantly increased leakage flux at the winding ends, and inability to transport normally will occur. This invention changes the single-body transformer structure into a double-body structure, where the first oil tank 1 and the first body group 105 form the first oil tank body unit, and the second oil tank 2 and the second body group 205 form the second oil tank body unit. In this way, the capacity of each oil tank body unit is half of the total capacity, which can avoid problems such as significantly increased winding temperature rise and significantly increased leakage flux at the winding ends. At the same time, it can also be split and transported separately, thus meeting transportation requirements.

[0038] However, there are several technical challenges in connecting the two tank body units in parallel: First, the parallel placement of the two tank body units places high demands on the height and width tolerance of the foundation, requiring adjustments to both tank body units. Second, the valve side insulation level of the ±800kV converter transformer is very high, and conventional bellows adjustment structures will cause distortion of the internal electric field, making it impossible to guarantee the insulation margin. Third, the ease of disassembly needs to be considered to meet transportation requirements.

[0039] To address the aforementioned problems, this invention firstly incorporates regulating bellows in the middle of both the parallel channel 3 of valve a and the parallel channel 4 of valve b, facilitating on-site installation and reducing the requirements for the flatness of the foundation. Secondly, this invention includes intermediate cable exit devices inside both regulating bellows. Furthermore, considering the presence of sharp corners, burrs, and other uneven electrodes on the inner surface of the regulating bellows, which can easily cause discharge, this invention utilizes a first shielding cylinder 8 on the intermediate cable exit device to fix and shield the uneven areas on the regulating bellows. A first corrugated cardboard cylinder 7 is used to ensure... The electric field strength and creepage distance are controlled by the intermediate equalizing sphere 14, which is used to connect the two connecting pipes. This ensures the electric field at the connection point and allows for increased adjustment range using the internal space of the sphere 14. This ensures assembly can be completed even with some height discrepancies between the two tank body units. Furthermore, when disassembling the two tank body units, simply detach the adjusting bellows from the lifting seat on either side, then separate the connecting pipe from the intermediate equalizing sphere 14. This allows for the separate disassembly and transportation of the two tank body units to the site for reinstallation. The equalizing sphere is a technology known in the art.

[0040] like Figures 8-10 As shown, in this embodiment, a first fixing clip 9 is provided between the first shielding cylinder 8 and the first cardboard corrugated cylinder 7 to fix the first cardboard corrugated cylinder 7. The first cardboard corrugated cylinder 7 is formed by multiple layers of cardboard and corrugated board.

[0041] like Figure 4 and Figure 7 As shown, in this embodiment, one end of the first shielding cylinder 8 is provided with a fixing plate 15 fixedly connected to the corresponding side lifting seat, and the other end is provided with a limiting insulating screw 16. When the adjusting bellows on the outside of the first shielding cylinder 8 is adjusted, the limiting insulating screw 16 can play a limiting and auxiliary support role. Especially when the adjusting bellows swings up and down to adjust the height, a certain height difference will be formed on both sides of the lifting seat. The limiting insulating screw 16 can limit the vertical displacement of the first shielding cylinder 8, thereby preventing the internal connecting pipe from detaching from the intermediate equalizing ball 14. In this embodiment, a cardboard ring can be provided at the end of the first shielding cylinder 8, and the cardboard ring is provided with threaded holes evenly around its circumference for installing the paper limiting insulating screw 16.

[0042] like Figure 9 As shown in this embodiment, pressure equalization pipes 10 are provided inside both ends of the first shielding cylinder 8.

[0043] like Figures 3-5As shown, in this embodiment, the parallel channel 3 of valve a includes a first valve a outlet device 304, a valve a intermediate outlet device 307, and a second valve a outlet device 305 connected sequentially via a valve a connecting pipe 308. The first valve a outlet device 304 is fixed to the first oil tank 1, and the second valve a outlet device 305 is fixed to the second oil tank 2. Figures 6-8 As shown, the parallel channel 4 of valve b includes a first valve b outlet device 404, a valve b intermediate outlet device 407, and a second valve b outlet device 405 connected sequentially via a valve b connecting pipe 408. The first valve b outlet device 404 is fixed to the second oil tank 2, and the second valve b outlet device 405 is fixed to the first oil tank 1. Figure 2 As shown, the first valve a outlet pipe 108 on the first device body assembly 105 is connected to the first valve a outlet device 304. The second valve a outlet pipe 208 on the second device body assembly 205 and the valve a parallel outlet pipe 309 led out from the second valve a outlet device 305 merge to form the valve a summary outlet pipe 207. The second valve b outlet pipe 206 on the second device body assembly 205 is connected to the first valve b outlet device 404. The first valve b outlet pipe 106 on the first device body assembly 105 and the valve b parallel outlet pipe 409 led out from the second valve b outlet device 405 merge to form the valve b summary outlet pipe 107.

[0044] like Figure 8 As shown, in this embodiment, the first valve a outlet device 304, the second valve a outlet device 305, the first valve b outlet device 404 and the second valve b outlet device 405 have the same structure. They all include a second shielding cylinder 11, a second fixing clamp 12 and a second cardboard corrugated cylinder 13 arranged sequentially from the outside to the inside. The second cardboard corrugated cylinder 13 is provided with an end equalizing ball 6 connecting the pipes on both sides.

[0045] like Figures 3-5 As shown, in this embodiment, the parallel channel 3 of valve a includes a first valve a riser seat 302, a valve a regulating bellows 301, and a second valve a riser seat 303 connected in sequence. The valve a regulating bellows 301 is provided with a valve a middle outlet device 307. The outer end of the first valve a riser seat 302 is fixedly connected to the first oil tank 1, and the outer end of the second valve a riser seat 303 is fixedly connected to the second oil tank 2. The outer sides of the outer ends of the first valve a riser seat 302 and the second valve a riser seat 303 are both provided with first housing shielding tubes 306. One end of the first valve a outlet device 304 is inserted into the first valve a riser seat 302, and one end of the second valve a outlet device 305 is inserted into the second valve a riser seat 303.

[0046] like Figures 6-8As shown, in this embodiment, the parallel channel 4 of valve b includes a first valve b riser seat 402, a valve b regulating bellows 401, and a second valve b riser seat 403 connected in sequence. The valve b regulating bellows 401 is provided with a valve b intermediate outlet device 407. The outer end of the first valve b riser seat 402 is fixedly connected to the second oil tank 2, and the outer end of the second valve b riser seat 403 is fixedly connected to the first oil tank 1. A second housing shielding tube 406 is provided on the outer side of the outer end of the first valve b riser seat 402 and the outer side of the outer end of the second valve b riser seat 403. One end of the first valve b outlet device 404 is inserted into the first valve b riser seat 402, and one end of the second valve b outlet device 405 is inserted into the second valve b riser seat 403.

[0047] like Figure 5 As shown, in this embodiment, the end equalizing ball 6 in the first valve a outlet device 304 connects the first valve a outlet pipe 108 to the corresponding side valve a connecting pipe 308. The middle equalizing ball 14 inside the valve a middle outlet device 307 connects the valve a connecting pipes 308 on both sides. The end equalizing ball 6 in the second valve a outlet device 305 connects the valve a parallel lead-out pipe 309 to the corresponding side valve a connecting pipe 308.

[0048] like Figure 8 As shown, in this embodiment, the end equalizing ball 6 in the first valve b outlet device 404 connects the second valve b outlet pipe 206 to the corresponding side valve b connecting pipe 408. The middle equalizing ball 14 inside the valve b middle outlet device 407 connects the valve b connecting pipes 408 on both sides. The end equalizing ball 6 in the second valve b outlet device 405 connects the valve b parallel lead-out pipe 409 to the corresponding side valve b connecting pipe 408.

[0049] The first valve a outlet pipe 108, the second valve a outlet pipe 208, the first valve b outlet pipe 106, the second valve b outlet pipe 206, the valve a connecting pipe 308, the valve a parallel lead-out pipe 309, the valve a general lead-out pipe 207, the valve b connecting pipe 408, the valve b parallel lead-out pipe 409, and the valve b general lead-out pipe 107 are all shielded pipes, and each of them is equipped with connecting cables to achieve electrical connection. This is a well-known technology in the field.

[0050] like Figures 1-2 As shown, in this embodiment, the parallel channel 3 of valve a is located on the upper side between the two oil tank body units, and the parallel channel 4 of valve b is located at the bottom between the two oil tank body units. The length and shape of the first valve a riser seat 302, the second valve a riser seat 303, the first valve b riser seat 402, and the second valve b riser seat 403 can be designed according to the actual needs of the site. During specific installation, adjustment is achieved through the valve a adjusting bellows 301 and the valve b adjusting bellows 401.

[0051] like Figures 1-2As shown, in this embodiment, the first oil tank 1 is equipped with a valve b sleeve 101, a first oil storage tank 102, a first mesh-side sleeve 103, and a first mesh-side neutral point sleeve 104; the second oil tank 2 is equipped with a valve a sleeve 201, a second oil storage tank 202, a second mesh-side sleeve 203, and a second mesh-side neutral point sleeve 204, wherein... Figure 2 As shown, the valve a main outlet pipe 207 is connected to the valve a sleeve 201, and the valve b main outlet pipe 107 is connected to the valve b sleeve 101. The electrical connections of each component are as follows: Figure 11 As shown.

[0052] Furthermore, oil-blocking baffles can be installed inside the parallel channel 3 of valve a and the parallel channel 4 of valve b as needed to block the oil connection between the first oil tank 1 and the second oil tank 2. The baffles have sealed through holes for the valve a connecting pipe 308 or the valve b connecting pipe 408 to pass through. The baffles can be installed in the riser seats on both sides, without affecting the disassembly and separate transportation of the transformer. And as... Figure 1 As shown, the two fuel tank body units can also share a cooler 5, which is a technology known in the art.

[0053] The working principle of this invention is as follows:

[0054] During installation, the two tank body units are placed side by side, with their upper adjacent sides connected via the valve a parallel channel 3 and their bottom adjacent sides connected via the valve b parallel channel 4. Both the valve a connecting pipe 308 (including its internal connecting wires) in the valve a parallel channel 3 and the valve b connecting pipe 408 (including its internal connecting wires) in the valve b parallel channel 4 need to have sufficient length to meet the adjustment requirements of the bellows' extension, retraction, or vertical swing. Simultaneously, the internal channel of the intermediate equalizing ball 14 also needs to have sufficient length to avoid interference between the connecting pipes on both sides during adjustment. The intermediate equalizing ball 14 is used to connect the connecting pipes on both sides. On the one hand, it can ensure the electric field at the connection point. On the other hand, the internal channel space of the intermediate equalizing ball 14 can further increase the adjustment range, so as to ensure that even if there is a certain deviation in the height of the two tank body units, the assembly can be completed. When the two tank body units need to be disassembled and transported, simply disassemble the adjusting bellows from the lifting seat on either side, and then separate the connecting pipe from the intermediate equalizing ball 14. The two tank body units can then be separated and transported separately, and reinstalled after being transported to the site. In addition, during installation and adjustment, since one end of the first shielding cylinder 8 is fixedly connected to the end of the corresponding side lifting seat, and the other end of the first shielding cylinder 8 is a free end, and the limiting insulating screw 16 can play a limiting and auxiliary support role, especially when adjusting the height of the bellows by swinging it up and down, a height difference will be formed between the two lifting seats. The limiting insulating screw 16 can limit the vertical displacement of the first shielding cylinder 8, thereby preventing the internal connecting pipe from detaching from the middle equalizing ball 14. At the same time, the limiting insulating screw 16 is threaded into the mounting hole of the wooden ring. Tightening the limiting insulating screw 16 can finely adjust its height, thereby further finely adjusting the vertical displacement of the first shielding cylinder 8, further improving the flexibility of on-site installation.

[0055] This invention changes the single-body structure of the upgraded converter transformer (750MVA, ±800kV) to a double-body parallel structure. This results in each tank body unit having a capacity of approximately 375MVA to 400MVA. Converter transformers within this range have extensive design experience and mature structures, effectively avoiding problems such as winding temperature rise and leakage flux overheating. Simultaneously, the size and weight of a single tank body unit meet transportation requirements. Furthermore, this invention only adds two lead connection channels: parallel channel 3 for valve a and parallel channel 4 for valve b. It does not significantly alter the transformer structure formed by a single tank body unit, thus avoiding increased design complexity and the number of valve-side bushings, saving costs.

[0056] However, considering the special nature of ultra-high voltage flexible DC transmission, the present invention presents problems such as how to perform on-site adjustment, how to avoid electric field distortion, and how to facilitate disassembly and transportation when the two tank body units are connected in parallel. In particular, the insulation level of the valve side of the ±800kV converter transformer is very high, and the conventional bellows adjustment structure will cause distortion of the internal electric field and cannot guarantee the insulation margin. This invention firstly incorporates regulating bellows in the middle of the parallel channel 3 of valve a and the middle of the parallel channel 4 of valve b to facilitate on-site installation and reduce the requirements for the flatness of the on-site foundation. Secondly, this invention includes intermediate cable exit devices inside both regulating bellows, and the intermediate cable exit devices include a first shielding cylinder 8 and a first cardboard corrugated cylinder 7 arranged sequentially from the outside to the inside. Considering that there may be uneven electrodes such as sharp corners and burrs on the inner surface of the regulating bellows, which can easily cause discharge, the first shielding cylinder 8 can fix and shield the uneven areas on the regulating bellows. The first cardboard corrugated cylinder 7 ensures the electric field strength and creepage distance. The intermediate equalizing ball 14 inside the first cardboard corrugated cylinder 7 is used for the connection of the two connecting pipes to ensure the electric field at the connection point, and can also further increase the adjustment range. It also facilitates the disassembly and separation of the two oil tank body units for separate transportation, which can meet the transportation requirements.

[0057] Because the parallel channel 3 of valve a and the parallel channel 4 of valve b of the present invention are located in the high field strength region on the valve side outlet side, they need to withstand more than 1 hour of 900kV AC withstand voltage test, more than 2 hours of 1200kV DC withstand voltage test, and more than 1.5 hours of polarity reversal withstand voltage test during production.

[0058] Other examples Figure 2 As shown, the present invention provides cable outlet devices at the connection points of the parallel channel 3 of valve a and the corresponding side oil tanks at both ends, and at the connection points of the parallel channel 4 of valve b and the corresponding side oil tanks at both ends. The cable outlet devices 304, 305, 404, and 405 of the first valve a, the second valve a, the first valve b, and the second valve b have the same structure, each including a second shielding cylinder 11, a second fixing clamp 12, and a second corrugated cardboard cylinder 13 arranged sequentially from the outside to the inside. The second corrugated cardboard cylinder 13 has an end equalizing ball 6 for pipeline connection, which can further ensure the insulation safety margin at both ends of the two parallel channels and improve the reliability of the product.

Claims

1. A parallel converter transformer for ultra-high voltage flexible DC transmission, characterized in that: It includes a first oil tank (1), a second oil tank (2), a parallel channel for valve a (3), and a parallel channel for valve b (4). The inlet end of the parallel channel for valve a (3) is fixed to the first oil tank (1), and the outlet end is fixed to the second oil tank (2). The inlet end of the parallel channel for valve b (4) is fixed to the second oil tank (2), and the outlet end is fixed to the first oil tank (1). The first oil tank (1) is equipped with a first body assembly (105), and the second oil tank (2) is equipped with a second body assembly (205). The first valve a outlet pipe (108) on the first body assembly (105) is connected to the inlet end of the parallel channel for valve a (3). The second valve a outlet pipe (208) on the second body assembly (205) merges with the parallel outlet pipe (309) of valve a (3) leading out from the outlet end of the parallel channel for valve a (3) to form a valve a general outlet pipe (207). The second valve b outlet pipe (206) on the second body assembly (205) is connected to the inlet end of the valve b parallel channel (4). The first valve b outlet pipe (106) on the first body assembly (105) and the valve b parallel outlet pipe (409) led out from the outlet end of the valve b parallel channel (4) are combined to form the valve b general outlet pipe (107). The middle part of the valve a parallel channel (3) and the middle part of the valve b parallel channel (4) are provided with adjusting bellows. The adjusting bellows are provided with lifting seats on both sides and an intermediate outlet device inside. The intermediate outlet device includes a first shielding cylinder (8) and a first cardboard corrugated cylinder (7) arranged sequentially from the outside to the inside. The first cardboard corrugated cylinder (7) is provided with an intermediate equalizing ball (14) connecting the two pipes inside. One end of the first shielding cylinder (8) is fixed on the lifting seat on the corresponding side and the other end is provided with a limiting insulating screw (16).

2. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: A first fixing clamp (9) is provided between the first shielding cylinder (8) and the first cardboard corrugated cylinder (7), and pressure equalization pipes (10) are provided at both ends of the first shielding cylinder (8).

3. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: The first shielding cylinder (8) has a cardboard ring at its end, and the cardboard ring is evenly provided with threaded holes around its circumference. The paper limiting insulating screw (16) is installed in the corresponding threaded hole.

4. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: The parallel channel (3) for valve a includes a first valve a outlet device (304), a valve a intermediate outlet device (307), and a second valve a outlet device (305) connected in sequence via a valve a connecting pipe (308). The first valve a outlet device (304) is fixed to the first oil tank (1), and the second valve a outlet device (305) is fixed to the second oil tank (2). The parallel channel (4) for valve b includes a first valve b outlet device (404), a valve b intermediate outlet device (407), and a second valve b outlet device (405) connected in sequence via a valve b connecting pipe (408). The device (404) is fixed on the second oil tank (2), and the second valve b outlet device (405) is fixed on the first oil tank (1); the first valve a outlet pipe (108) is connected to the first valve a outlet device (304), the second valve a outlet pipe (208) merges with the valve a parallel outlet pipe (309) led out from the second valve a outlet device (305), the second valve b outlet pipe (206) is connected to the first valve b outlet device (404), and the first valve b outlet pipe (106) merges with the valve b parallel outlet pipe (409) led out from the second valve b outlet device (405).

5. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 4, characterized in that: The first valve a outlet device (304), the second valve a outlet device (305), the first valve b outlet device (404), and the second valve b outlet device (405) have the same structure. They all include a second shielding cylinder (11), a second fixing clamp (12), and a second cardboard corrugated cylinder (13) arranged sequentially from the outside to the inside. The second cardboard corrugated cylinder (13) is provided with an end equalizing ball (6) connecting the pipes on both sides.

6. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 4, characterized in that: The parallel channel (3) of valve a includes a first valve a riser seat (302), a valve a regulating bellows (301), and a second valve a riser seat (303) connected in sequence. The valve a regulating bellows (301) is provided with a valve a middle outlet device (307). The outer end of the first valve a riser seat (302) is fixedly connected to the first oil tank (1), and the outer end of the second valve a riser seat (303) is fixedly connected to the second oil tank (2). The outer side of the outer end of the first valve a riser seat (302) and the outer side of the outer end of the second valve a riser seat (303) are both provided with a first housing shielding tube (306). One end of the first valve a outlet device (304) is inserted into the first valve a riser seat (302), and one end of the second valve a outlet device (305) is inserted into the second valve a riser seat (303).

7. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 4, characterized in that: The parallel channel (4) of valve b includes a first valve b riser seat (402), a valve b regulating bellows (401), and a second valve b riser seat (403) connected in sequence. The valve b regulating bellows (401) is provided with a valve b intermediate outlet device (407). The outer end of the first valve b riser seat (402) is fixedly connected to the second oil tank (2), and the outer end of the second valve b riser seat (403) is fixedly connected to the first oil tank (1). The outer side of the outer end of the first valve b riser seat (402) and the outer side of the outer end of the second valve b riser seat (403) are both provided with a second housing shield tube (406). One end of the first valve b outlet device (404) is inserted into the first valve b riser seat (402), and one end of the second valve b outlet device (405) is inserted into the second valve b riser seat (403).

8. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: The valve a parallel channel (3) is located on the upper side between the first oil tank (1) and the second oil tank (2), and the valve b parallel channel (4) is located at the bottom between the first oil tank (1) and the second oil tank (2).

9. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: The first oil tank (1) is provided with valve b sleeve (101), first oil storage tank (102), first mesh side sleeve (103) and first mesh side neutral point sleeve (104). The second oil tank (2) is provided with valve a sleeve (201), second oil storage tank (202), second mesh side sleeve (203) and second mesh side neutral point sleeve (204). The valve a collection outlet pipe (207) is connected to the valve a sleeve (201), and the valve b collection outlet pipe (107) is connected to the valve b sleeve (101).

10. The parallel converter transformer for ultra-high voltage flexible DC transmission according to claim 1, characterized in that: Both the parallel channel (3) of valve a and the parallel channel (4) of valve b are equipped with oil-blocking baffles that block the oil connection between the first oil tank (1) and the second oil tank (2).

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