Transformer bushing

Abstract

This application discloses a transformer bushing, comprising a conductive rod and a head assembly, a composite insulator, an intermediate flange, and a tail assembly connected in sequence. The conductive rod passes through the head assembly, composite insulator, intermediate flange, and tail assembly in sequence. The oil conservator of the head assembly includes an interconnected cabinet and end caps, with at least one pressure relief device on the end caps. The second end of the cabinet is fixed to the first end of the composite insulator, the second end of the composite insulator is fixed to the first end of the intermediate flange, and the second end of the intermediate flange is fixed to the first end of the oil-insulated tube in the tail assembly using adhesive. The internal pressure of the oil conservator during failure is greater than the internal pressure of the composite insulator during failure but less than the internal pressure of the oil-insulated tube during failure. The solution of this application can ensure the structural integrity of the transformer bushing during operation and prevent transformer oil leakage due to damage to the transformer bushing.

Description

Technical Field

[0001] This application relates to the field of power transmission and transformation technology, and in particular to a transformer bushing. Background Technology

[0002] Existing oil-paper capacitor bushings generally use porcelain insulators as external insulation. These are prone to breakage during arcing faults, leading to bushing seal failure, transformer oil leakage, and potentially combustion or explosion. Furthermore, porcelain insulators are brittle, and exploding porcelain fragments can easily cause secondary accidents. Additionally, there is no limiting structure between the metal parts and the insulators. The cable joint is connected to the cap via a threaded connection, and the bottom equalizing ball is connected to the oil-insulating tube via a threaded connection or spring clamp. During operation, when the bushing is subjected to bending moments, the connection structure between the metal parts and the insulators is prone to displacement and damage, leading to oil leakage and other problems. Moreover, traditional oil-paper capacitor bushings lack pressure relief devices. When an arcing fault occurs inside the bushing, excessive internal pressure can be generated, potentially damaging transformer bushing components if not relieved beforehand. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this application is to provide a transformer bushing that can ensure the structural integrity of the transformer bushing during operation and prevent transformer oil leakage due to damage to the transformer bushing.

[0004] To achieve the above objectives, the technical means adopted in this application are as follows: A transformer bushing is provided, comprising a conductive rod and a head assembly, a composite insulator, an intermediate flange, and a tail assembly that are fixedly connected in sequence. The conductive rod passes through the head assembly, the composite insulator, the intermediate flange, and the tail assembly in sequence. The oil conservator of the head assembly includes a cabinet and an end cover that are connected to each other. At least one pressure relief device is provided on the end cover. The second end of the cabinet is fixed to the first end of the composite insulator, the second end of the composite insulator is fixed to the first end of the intermediate flange, and the second end of the intermediate flange is fixed to the first end of the oil-insulating tube of the tail assembly by adhesive. The internal pressure of the oil conservator is greater than the internal pressure of the composite insulator and less than the internal pressure of the oil-insulating tube.

[0005] In one embodiment, the composite insulator includes an insulating tube, which is made by impregnating fibers with resin and then winding and curing them, with the winding angle of the fibers being 30° to 60°.

[0006] In one embodiment, the ratio of the adhesive height of the insulating tube to the outer diameter of the insulating tube ranges from 0.2 to 0.4, and / or the ratio of the adhesive height of the insulating tube in the oil to the outer diameter of the insulating tube in the oil ranges from 0.2 to 0.4.

[0007] In one embodiment, the adhesive strength of the composite insulator is greater than the breaking strength of the composite insulator, and / or, the adhesive strength of the oil-insulated tube is greater than the breaking strength of the oil-insulated tube.

[0008] In one embodiment, the adhesive fixing is performed by filling with adhesive, and the filling gap of the adhesive is in the radial direction of the transformer bushing, ranging from 0.25 mm to 0.5 mm.

[0009] In one embodiment, the oil-insulating tube is made by impregnating fibers with resin and then winding and curing them, wherein the winding angle of the fibers is greater than or equal to 70° and less than 90°.

[0010] In one embodiment, the oil-insulating tube is made by impregnating fibers with resin and then winding and curing them. The fibers form multiple insulating layers, and the multiple insulating layers include at least one circumferential winding layer and one inclined winding layer. The winding angle of the fibers in the circumferential winding layer is greater than or equal to 80° and less than 90°, and the winding angle of the fibers in the inclined winding layer is 30° to 60°.

[0011] In one embodiment, the thickness of the insulating tube in the oil is greater than the thickness of the insulating tube in the composite insulator.

[0012] In one embodiment, the fiber is glass fiber or aramid fiber, and / or the resin is epoxy resin or phenolic resin.

[0013] In one embodiment, the end cap is provided with a stepped hole, and the pressure relief device includes a plug, a spring and a pressure plate. The plug is disposed in the stepped hole, the spring is sleeved on the plug, and the pressure plate presses down on the spring and is fixedly connected to the end cap.

[0014] The beneficial effects of this application are as follows: Unlike the prior art, the transformer bushing provided in this application uses adhesive bonding to achieve a fixed connection between the tank body and composite insulator, the composite insulator and intermediate flange, and the intermediate flange and oil-insulating pipe. The connection is reliable. Furthermore, by setting a reasonable internal pressure gradient relationship between the various components of the transformer bushing, i.e., the internal pressure of the oil-insulating pipe > the internal pressure of the tank > the internal pressure of the composite insulator, priority is given to ensuring that the oil-insulating pipe does not break, followed by the tank and intermediate flange, and finally the composite insulator. This ensures the structural integrity of the transformer bushing and prevents transformer oil leakage due to damage to the transformer bushing. By installing at least one pressure relief device on the transformer bushing, when an arc fault occurs in the transformer bushing in the oil, the pressure generated will be discharged from the pressure relief device first, preventing damage to the transformer bushing components and significantly improving the safety and reliability of the transformer bushing.

[0015] This application further sets the adhesive strength to be greater than the breaking strength of each structure itself, prioritizing the strength of the connection structure. Simultaneously, the transformer bushing uses composite insulators as the outer insulation structure. The insulating tube, through its winding angle design, possesses excellent mechanical strength and toughness, preventing explosion even under extreme conditions of excessive internal pressure. The oil-insulated tube employs a large-angle winding design or a combination of small-angle winding and circumferential winding, allowing it to withstand greater internal pressure without damage. Compared to traditional porcelain bushing technology, this avoids the risk of porcelain bushing explosions due to arcing faults within the transformer or transformer bushing, thereby preventing severe secondary injuries from flying porcelain fragments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a transformer bushing 100 according to an embodiment of this application;

[0017] Figure 2 yes Figure 1 Enlarged view of point A in the middle;

[0018] Figure 3 yes Figure 1 Enlarged view of point B in the middle;

[0019] Figure 4 yes Figure 3 Enlarged view of point C in the middle;

[0020] Figure 5 yes Figure 1 A top view of the cross-sectional section of the transformer bushing 100. Detailed Implementation

[0021] As requested, specific embodiments of this application are disclosed herein. However, it should be understood that the embodiments disclosed herein are merely typical examples of this application and may be embodied in various forms. Therefore, the specific details disclosed herein are not intended to be limiting, but merely to serve as the basis for the claims and as a representative basis for teaching those skilled in the art to apply this application differently in practice in any appropriate manner, including employing the various features disclosed herein in combination with features that may not be explicitly disclosed herein.

[0022] like Figure 1As shown, this application provides a transformer bushing 100, including a head assembly 110, a conductive rod 120, a composite insulator 130, an intermediate flange 140, and a tail assembly 150. The head assembly 110, composite insulator 130, intermediate flange 140, and tail assembly 150 are sequentially fixedly connected. The conductive rod 120 is sequentially passed through the head assembly 110, composite insulator 130, intermediate flange 140, and tail assembly 150. The head assembly 110 includes an oil conservator 111 and a terminal block 112. The conductive rod 120 is located at one end of the head assembly 110 and is fixedly connected to the terminal block 112 for connecting the transformer bushing 100 to an external line. The tail assembly 150 includes an oil-insulated tube 151 and a base 152. A conductive rod 120 is located at the other end of the tail assembly 150 and is fixedly connected to the base 152 via a threaded structure, ensuring the conductive rod 120 is securely positioned within the transformer bushing 100. This prevents the conductive rod 120 from shifting due to thermal expansion and contraction during operation of the transformer bushing 100. The connections between the conductive rod 120 and the terminal block 112, and between the conductive rod 120 and the base 152, are sealed connections, ensuring the sealing of all connections within the transformer bushing 100 and thus guaranteeing the long-term reliability of the transformer bushing 100. The axial directions of the composite insulator 130, the oil-insulated tube 151, and the transformer bushing 100 coincide.

[0023] The composite insulator 130 includes an insulating tube 131 and a shed 132 covering the outer periphery of the insulating tube 131. The insulating tube 131 is made of fiber-reinforced resin composite material, specifically fiber material impregnated with resin material and then cured. The fiber material can be any of the reinforcing fibers such as glass fiber and aramid fiber, and the resin material can be any of the thermosetting resins such as epoxy resin and phenolic resin. This gives the insulating tube 131 good mechanical strength and toughness, and it will not explode even under extreme conditions of excessive internal pressure.

[0024] In one embodiment, the insulating tube 131 is formed by impregnating fibers with resin and then curing them through a winding process. The angle between the winding direction of the fibers and the axial direction of the insulating tube 131 is defined as the fiber winding angle. The fiber winding angle of the insulating tube 131 is set to 30° to 60°, giving the insulating tube 131 higher bending strength and better bending resistance. The umbrella skirt 132 is integrally injection molded from high-temperature vulcanized silicone rubber. High-temperature vulcanized silicone rubber has good hydrophobicity and hydrophobic migration properties, as well as excellent resistance to pollution flashover, rain flashover, and ice flashover. In other embodiments, the insulating tube 131 can also be formed by impregnating fibers with resin and then curing them through a stretching process; this is not a limitation.

[0025] The materials and manufacturing method of the oil-insulating tube 151 are similar to those of the insulating tube 131. In one embodiment, when the oil-insulating tube 151 is made by impregnating fibers with resin and then curing them through a winding process, the winding angle of the fibers in the oil-insulating tube 151 is greater than or equal to 70° and less than 90°. That is, the oil-insulating tube 151 adopts a large-angle winding, which can improve the circumferential pressure bearing capacity of the oil-insulating tube 151 and can withstand greater internal pressure than the insulating tube 131. In other embodiments, the fibers of the oil-insulating tube 151 can also be wound using a combination of small-angle winding and circumferential winding. In this case, the fibers of the oil-insulating tube 151 are arranged at multiple angles, that is, the fibers of the oil-insulating tube 151 form multiple insulating layers. The multiple insulating layers include at least one circumferential winding layer and one inclined winding layer, which are spaced apart. The winding angle of the fibers in the circumferential winding layer is greater than or equal to 80° and less than 90°. The fibers in the inclined winding layer are wound at a small angle, with the winding angle set to 30° to 60°. Using multiple winding angles can improve the mechanical strength of the oil-insulating tube 151, ensuring that the internal pressure that the oil-insulating tube 151 can withstand is greater than the internal pressure that the composite insulator 130 can withstand. Furthermore, under the same inner diameter, the thickness of the oil-insulating tube 151 can be reduced as much as possible to save costs.

[0026] In this application, "specified internal pressure" (SIP) is used to characterize the strength of each component under internal pressure. According to IEC 61462-2023, "Composite hollow insulators - Pressurized and unpressurized insulators for use in electrical equipment with AC rated voltage greater than 1000 V AC and DC voltage greater than 1500 V - Definitions, test methods, acceptance criteria and design recommendations," the specified internal pressure is defined as the short-time withstand design limit. Under this limit, the insulator structure remains intact, but damage may have occurred. In this application, the specified internal pressure is a design value, derived through the structural and dimensional design of components such as insulating tubes. The thickness of the oil-insulating tube 151 is set to be greater than that of the insulating tube 131. Combined with the fiber winding angle design, this ensures that the specified internal pressure of the oil-insulating tube 151 is greater than that of the insulating tube 131. At the same time, the breaking internal pressure of the same component is positively correlated with the specified internal pressure. The specified internal pressure value of the insulating tube 131 is the same as the specified internal pressure value of the composite insulator 130. Therefore, the breaking internal pressure of the oil-insulating tube 151 is greater than that of the composite insulator 130. When a fault occurs inside the transformer bushing 100 under extreme operating conditions, priority is given to ensuring that the oil-insulating tube 151 is not damaged, which can avoid damage to the inside of the transformer and reduce the severity of the fault.

[0027] Combination Figure 2As shown, the oil conservator 111 includes a cabinet body 1111 and an end cover 1112 connected to each other. The cabinet body 1111 is a hollow columnar structure, and the end cover 1112 is a circular plate. The end of the cabinet body 1111 closest to the terminal block 112 is defined as the first end of the cabinet body 1111, and the other end is defined as the second end of the cabinet body 1111. The axial direction of the oil conservator 111 coincides with the axial direction of the transformer bushing 100. The end of the composite insulator 130 closest to the head assembly 110 is defined as the first end of the composite insulator 130, and the other end is defined as the second end of the composite insulator 130. The second end of the cabinet body 1111 is fixedly connected to the first end of the composite insulator 130. Specifically, adhesive is filled between the cabinet body 1111 and the insulating tube 131 to achieve adhesive fixation between the oil conservator 111 and the insulating tube 131. That is, adhesive fixation is achieved by filling adhesive. An annular first protrusion is provided on the inner wall of the second end of the cabinet 1111. The end face of the first protrusion near the composite insulator 130 is a first stepped surface 11111, which is used to abut against the end face of the insulating tube 131 for easy positioning and installation. A first sealing groove 11112 is provided on the first stepped surface 11111, and a first sealing element is provided within the first sealing groove 11112 to maintain a sealed connection between the oil conservator 111 and the composite insulator 130, preventing external moisture, impurities, etc., from entering the oil conservator 111. The first sealing element is made of oil-resistant and high-temperature-resistant rubber material, such as nitrile rubber, fluororubber, etc., without limitation. The first sealing groove 11112 can also be provided on the end face of the insulating tube 131, or the first sealing groove 11112 can be provided simultaneously on the first stepped surface 11111 of the cabinet 1111 and the end face of the insulating tube 131, ensuring that the first sealing element is completely engaged between the insulating tube 131 and the cabinet 1111, without limitation.

[0028] The inner wall of the second end of the cabinet 1111 is provided with several annular first adhesive grooves 11113, which are spaced apart along the axial direction of the cabinet 1111. The outer wall of the end of the insulating tube 131 located at the first end of the composite insulator 130 is provided with several annular second adhesive grooves 1311, which are spaced apart along the axial direction of the composite insulator 130 and correspond to the several first adhesive grooves 11113. The inner diameter of the cabinet 1111 is slightly larger than the outer diameter of the insulating tube 131. After the insulating tube 131 is inserted into the inner cavity of the cabinet 1111, a filling gap for filling adhesive is formed between the outer wall of the insulating tube 131 and the inner wall of the cabinet 1111. The size of this filling gap along the radial direction of the transformer bushing 100 ranges from 0.25 mm to 0.5 mm. After the adhesive is fully filled into the gaps, the first adhesive groove 11113 and the second adhesive groove 1311 and cured, the cabinet 1111 is glued and fixed to the composite insulator 130.

[0029] By using adhesive bonding, the composite insulator 130 and the oil conservator 111 are completely confined in the axial and circumferential directions, preventing relative sliding and separation. This effectively prevents transformer oil leakage caused by the separation of the composite insulator 130 and the oil conservator 111 during internal faults or stress in the transformer bushing 100. Simultaneously, the installation of a first sealing element ensures a sealed connection between the composite insulator 130 and the oil conservator 111.

[0030] The length of the adhesive filling along the axial direction on the outer wall of the insulating tube 131 is defined as the adhesive height of the insulating tube 131. The ratio of the adhesive height at the first end of the insulating tube 131 located at the first end of the composite insulator 130 to the outer diameter of the insulating tube 131 ranges from 0.2 to 0.4, ensuring that the adhesive strength at the first end of the composite insulator 130 is greater than the breaking strength of the composite insulator 130. This prevents excessive internal pressure from damaging the adhesive area connecting the composite insulator 130 to the oil conservator 111, which could lead to the disintegration of the transformer bushing 100. Adhesive strength refers to the ultimate stress or ultimate load value corresponding to the loss of connection capacity and failure of the adhesive structure under a specific load. The breaking strength of the composite insulator 130 refers to the ultimate stress or ultimate load value corresponding to the loss of load-bearing capacity and failure of the composite insulator 130 under a specific load due to material failure, instability, or fracture.

[0031] Combination Figure 3 As shown, the first end of the cabinet 1111 is fixedly connected to the end cover 1112. Several first connecting holes are provided on the end face of the first end of the cabinet 1111, and several second connecting holes corresponding to the first connecting holes are provided on the end cover 1112. Fasteners are passed through the second connecting holes and the first connecting holes to securely connect the first end of the cabinet 1111 to the end cover 1112. Simultaneously, a second sealing groove 11114 is provided on the end face of the cabinet 1111 that connects to the end cover 1112. A second sealing element is installed within the second sealing groove 11114 to seal and fix the cabinet 1111 to the end cover 1112, preventing external moisture, impurities, etc., from entering the oil tank 111. The material of the second sealing element is the same as that of the first sealing element, and will not be described further. The second sealing groove 11114 can also be located on the end face of the end cover 1112 that connects to the cabinet 1111, or the second sealing groove 11114 can be located on both the end cover 1112 and the cabinet 1111; no limitation is imposed here.

[0032] Continue reading Figure 1The intermediate flange 140 is a hollow columnar structure. The end of the intermediate flange 140 closest to the head assembly 110 is defined as the first end of the intermediate flange 140, and the other end is the second end. The axial direction of the intermediate flange 140 coincides with the axial direction of the transformer bushing 100. The first end of the intermediate flange 140 is fixedly connected to the second end of the composite insulator 130, specifically by adhesive bonding, similar to the connection method between the second end of the aforementioned cabinet 1111 and the first end of the composite insulator 130, and will not be described again. Simultaneously, a third sealing groove is provided between the connecting end faces of the intermediate flange 140 and the composite insulator 130. A third sealing element is installed within the third sealing groove to seal and fix the intermediate flange 140 and the composite insulator 130, preventing moisture from entering the composite insulator 130 from the intermediate flange 140. The location of the third sealing groove is similar to that of the first sealing groove, and the material of the third sealing element is the same as that of the first sealing element, and will not be described again. The ratio of the adhesive height of the end of the insulating tube 131 located at the second end of the composite insulator 130 to the outer diameter of the insulating tube 131 ranges from 0.2 to 0.4. This ensures that the adhesive strength at the second end of the composite insulator 130 is greater than the breaking strength of the composite insulator 130, preventing excessive internal pressure from damaging the adhesive area connecting the composite insulator 130 to the intermediate flange 140 and causing the transformer bushing 100 to disintegrate. The definitions of adhesive strength and the breaking strength of the composite insulator 130 are consistent with those described above.

[0033] By using adhesive bonding, the composite insulator 130 and the intermediate flange 140 are completely confined in the axial and circumferential directions, preventing relative sliding and separation. This effectively prevents transformer oil leakage caused by the separation of the composite insulator 130 and the intermediate flange 140 during internal faults or stress in the transformer bushing 100. Simultaneously, a third sealing element ensures a sealed connection between the composite insulator 130 and the intermediate flange 140.

[0034] The end of the oil-insulating tube 151 closest to the head assembly 110 is defined as the first end of the oil-insulating tube 151, and the other end is the second end of the oil-insulating tube 151. The second end of the intermediate flange 140 is fixedly connected to the first end of the oil-insulating tube 151 by adhesive, specifically in the same way as the connection between the second end of the cabinet 1111 and the first end of the composite insulator 130, which will not be described again. A fourth sealing groove is provided between the connecting end faces of the intermediate flange 140 and the oil-insulating tube 151, and a fourth sealing element is provided in the fourth sealing groove to seal and fix the intermediate flange 140 and the oil-insulating tube 151, preventing moisture from entering the oil-insulating tube 151 from the intermediate flange 140. The setting position of the fourth sealing groove is similar to that of the first sealing groove, and the material of the fourth sealing element is the same as that of the first sealing element, which will not be described again.

[0035] The length of the adhesive filling along the axial direction on the outer wall of the oil-insulating tube 151 is defined as the adhesive height of the oil-insulating tube 151. The ratio of the adhesive height at the first end of the oil-insulating tube 151 to its outer diameter is in the range of 0.2 to 0.4, ensuring that the adhesive strength at the first end of the oil-insulating tube 151 is greater than its breaking strength. This prevents excessive internal pressure from damaging the adhesive area at the first end of the oil-insulating tube 151, which could lead to the disintegration of the transformer bushing 100. The definition of adhesive strength is consistent with the aforementioned definition. The breaking strength of the oil-insulating tube 151 refers to the ultimate stress or ultimate load value corresponding to the loss of load-bearing capacity and failure of the oil-insulating tube 151 under a specific load due to material failure, instability, or fracture.

[0036] Furthermore, the second end of the oil-insulating tube 151 is also fixed to the base 152 by adhesive bonding, specifically in the same way as the connection between the second end of the cabinet 1111 and the first end of the composite insulator 130, which will not be described again. A fifth sealing groove is provided between the connecting end faces of the oil-insulating tube 151 and the base 152, and a fifth sealing element is installed in the fifth sealing groove to seal and fix the oil-insulating tube 151 and the base 152, preventing moisture from entering the oil-insulating tube 151 from the base 152. The location of the fifth sealing groove is similar to that of the first sealing groove, and the material of the fifth sealing element is the same as that of the first sealing element, which will not be described again. The ratio of the adhesive bonding height of the second end of the oil-insulating tube 151 to the outer diameter of the oil-insulating tube 151 is in the range of 0.2 to 0.4, so that the adhesive bonding strength of the second end of the oil-insulating tube 151 is greater than the breaking strength of the oil-insulating tube 151, preventing excessive internal pressure from damaging the adhesive bonding area of ​​the second end of the oil-insulating tube 151 and causing the transformer bushing 100 to disintegrate. The definitions of adhesive strength and the breaking strength of the oil-insulated tube 151 are consistent with those described above.

[0037] The oil tank 111 and the intermediate flange 140 are both made of metal, such as cast aluminum alloy ZL101A or stainless steel.

[0038] Furthermore, the specified internal pressure of the oil conservator 111 is set to be greater than the specified internal pressure of the composite insulator 130 and less than the specified internal pressure of the oil-insulating pipe 151. This specified internal pressure gradient relationship can be achieved through the precise design of material selection and structural thickness. That is, the failure internal pressure of the oil conservator 111 is greater than the failure internal pressure of the composite insulator 130 and less than the failure internal pressure of the oil-insulating pipe 151. At the same time, the failure internal pressure of the intermediate flange 140 is designed to be approximately equal to the failure internal pressure of the oil conservator 111. That is, the failure internal pressures of the two can be the same or different, but the difference between the two failure internal pressures is within the preset safety tolerance range. Therefore, the failure internal pressure of the main cavity structure of the transformer bushing 100 satisfies the following gradient relationship:

[0039] The internal pressure at which the insulating tube 151 breaks down is greater than the internal pressure at which the oil conservator 111 breaks down, which is approximately equal to the internal pressure at which the intermediate flange 140 breaks down, which is greater than the internal pressure at which the composite insulator 130 breaks down.

[0040] When a fault occurs inside the transformer bushing 100, priority is given to preventing the oil-insulated tube 151 from breaking. This avoids damage to the transformer's internal structure and reduces the severity of the fault. This is because if the oil-insulated tube 151 breaks, its fragments will damage the insulating windings inside the transformer tank and contaminate the transformer oil, leading to an escalation of the accident and losses. Therefore, its specified internal pressure is set to the highest strength level, resulting in the highest failure internal pressure. This fundamentally prevents damage to the core internal components of the transformer and reduces the severity of the fault. Secondly, priority is given to preventing damage to the oil conservator 111 and intermediate flange 140. To prevent such metal parts from shattering due to excessive internal pressure, causing metal fragments to fly and causing secondary damage to surrounding equipment and personnel; and finally, to ensure that the composite insulator 130 does not shatter. Because the insulating tube 131 of the composite insulator 130 is made of fiber-reinforced resin composite material, it has high mechanical strength and good toughness and can withstand large internal pressure impacts. Even if the internal pressure exceeds the design limit, its failure mode is mainly manifested as axial cracking or delamination, rather than brittle explosion or complete disintegration like traditional ceramic materials. That is, it will not cause secondary damage or a large amount of transformer oil leakage, thus reducing losses.

[0041] A capacitor core 160 is also provided outside the conductive rod 120. The capacitor core 160 is composed of a hollow aluminum tube wound with cable paper of a certain thickness according to the design dimensions and covered with a layer of aluminum foil, serving as the main insulation structure of the transformer bushing 100. At the same time, a spring assembly is installed inside the oil conservator 111 to ensure that the conductive rod 120 is equipotentially connected to the oil conservator 111, while also centering the capacitor core 160 and subjecting it to a slight upward tension. This prevents the glued area at the second end of the insulating tube 151 in the oil from bearing the weight of the capacitor core 160, thus providing shock resistance for the entire transformer bushing 100.

[0042] Continue to combine Figure 1 and Figure 3As shown, the oil tank 111 is equipped with a pressure relief device 170, which is located on the end cover 1112. The pressure relief device 170 includes a plug 171, a spring 172, a pressure plate 173, a sealing plate 174, a fastening plate 175, and a waterproof cap 176. The end cover 1112 is provided with a stepped hole 11121 penetrating the end cover 1112. The axial direction of the stepped hole 11121 is parallel to the axial direction of the oil tank 111. The stepped hole 11121 includes a first through hole and a second through hole that are connected to each other along its axial direction. The diameter of the first through hole is smaller than the diameter of the second through hole. A second stepped surface 11122 is formed between the first through hole and the second through hole. The first through hole is located close to the tank body 1111 to connect to the inner cavity of the tank body 1111, and the second through hole is located away from the tank body 1111 to connect to the outside air. The pressure relief device 170 is connected to the stepped hole 11121. The plug 171 includes a plug body with a columnar structure and a second protrusion surrounding the outer periphery of the plug body. The outer diameter of the second protrusion is larger than the diameter of the first through hole and slightly smaller than the diameter of the second through hole. The plug 171 is disposed in the stepped hole 11121. One end of the plug body passes through the first through hole from the second through hole, and the second protrusion abuts against the second stepped surface 11122, that is, the plug 171 is stuck on the second stepped surface 11122, which is used to isolate the inner cavity of the oil tank 111 from the external air environment. At this time, the other end of the plug body is located in the second through hole, and the axial direction of the plug 171 coincides with the axial direction of the stepped hole 11121. A sixth sealing element is provided between the plug 171 and the second stepped surface 11122. When the second protrusion of the plug 171 abuts against the second stepped surface 11122, the plug 171 can fully compress the sixth sealing element, making the plug 171 and the second stepped surface 11122 form a sealed connection. Consequently, during normal operation, the interior of the transformer bushing 100 can be sealed and isolated from the external ambient air. The sixth sealing element is the first seal of the pressure relief device 170 and is the main sealing structure of the pressure relief device 170, preventing the external ambient air from communicating with the inner cavity of the oil conservator 111 due to the setting of the stepped hole 11121 during normal operation of the transformer bushing 100. The material of the sixth sealing element is the same as that of the first sealing element, and will not be described again.

[0043] Combination Figure 3 and Figure 4As shown, spring 172 is sleeved on the outer periphery of plug body located in second through hole of plug 171. Pressure plate 173 covers spring 172, sealing plate 174 covers end face of pressure plate 173 away from end cover 1112, and fastening plate 175 covers end face of sealing plate 174 away from pressure plate 173. Fasteners are sequentially inserted through fastening plate 175, sealing plate 174 and pressure plate 173 to fix pressure plate 173, sealing plate 174 and fastening plate 175 sequentially to end cover 1112. Waterproof cap 176 is sleeved and installed on the outermost side of pressure relief device 170, that is, sleeved on the outside of fastening plate 175, sealing plate 174 and pressure plate 173. The end cap 1112 is provided with a plurality of first mounting holes, the pressure plate 173 is provided with a plurality of second mounting holes corresponding to the first mounting holes, the sealing plate 174 is provided with a plurality of third mounting holes corresponding to the plurality of second mounting holes, and the fastening plate 175 is provided with a plurality of fourth mounting holes corresponding to the plurality of third mounting holes. The fasteners are sequentially passed through the fourth mounting holes, the third mounting holes, the second mounting holes and the first mounting holes, so that the fastening plate 175, the sealing plate 174, the pressure plate 173 are fastened to the end cap 1112. At the same time, the pressure plate 173 compresses the spring 172, so that the spring 172 applies pressure to the plug 171 to seal the first through hole of the stepped hole 11121, preventing external moisture, impurities and the like from entering the oil tank 111 through the stepped hole 11121.

[0044] The pressure plate 173 is a circular annular plate with a central opening, made of metal. On one hand, the pressure plate 173 is used to compress the spring 172; on the other hand, the opening on the pressure plate 173 allows the second through-hole of the stepped hole 11121 to connect with external air. Furthermore, when the plug 171 is pushed out by the internal pressure within the transformer bushing 100, the pressure can be quickly released from the central opening of the pressure plate 173. The sealing plate 174 is a circular plate made of a low-strength, oil-resistant rubber material, facilitating its removal when internal pressure is excessive. Materials such as nitrile rubber or fluorosilicone rubber are used to prevent oil leakage caused by the failure of the sixth seal and to avoid the problem of the pressure relief device 170 failing to release pressure quickly in case of a malfunction due to excessive mechanical strength. The fastening plate 175 is a circular plate made of metal; it can be a flat plate or a circular annular plate with a central opening, used to press the sealing plate 174. The axial direction of the pressure plate 173, the axial direction of the sealing plate 174, and the axial direction of the fastening plate 175 all coincide with the axial direction of the stepped hole 11121. Furthermore, the outer diameters of the pressure plate 173, the sealing plate 174, and the fastening plate 175 are all equal, so that the outer peripheral surfaces of the pressure plate 173, the sealing plate 174, and the fastening plate 175 are flush after installation, making it easy for the waterproof cap 176 to fit the pressure plate 173, the sealing plate 174, and the fastening plate 175 as a whole.

[0045] The stepped hole 11121 also includes a third through hole portion, which is connected to the second through hole portion. The second through hole portion is located between the first through hole portion and the third through hole portion. The axial direction of the third through hole portion coincides with the axial direction of the second through hole portion, and the diameter of the third through hole portion is larger than the diameter of the second through hole portion, so that a third stepped surface 11123 is formed between the second through hole portion and the third through hole portion. A third boss is provided on the end face of the pressure plate 173 facing the stepped hole 11121. The third boss is an annular columnar structure. The axial direction of the third boss coincides with the axial direction of the pressure plate 173. The third boss protrudes from the end face of the pressure plate 173 facing the stepped hole 11121, and the outer diameter of the third boss is smaller than the outer diameter of the pressure plate 173, so that a first groove 1731 is formed between the third boss and the end face of the pressure plate 173 facing the stepped hole 11121. Furthermore, the outer diameter of the third boss is smaller than the diameter of the third through hole. When the pressure plate 173 is fixedly connected to the end cover 1112, the third boss abuts against the compression spring 172, and the groove surface of the first groove 1731 facing the end cover 1112 abuts against the end cover 1112. A space is then formed between the third boss and the wall of the third through hole, which is the seventh sealing groove. A seventh sealing element 1732 is installed in the seventh sealing groove to seal and fix the pressure plate 173 and the end cover 1112. The material of the seventh sealing element 1732 is the same as that of the first sealing element, and will not be described further. Simultaneously, the axial height of the third boss is less than or equal to the axial height of the third through hole to prevent the groove surface of the first groove 1731 facing the end cover 1112 from failing to abut against the end cover 1112 when the pressure plate 173 compresses the spring 172, thus affecting the sealing and fixing of the pressure plate 173 and the end cover 1112. The seventh seal is used to prevent gas from entering or leaving through the gap at the connection between the pressure plate 173 and the end cover 1112. The sealing plate 174 is used to prevent gas from entering or leaving through the opening in the center of the pressure plate 173. The seventh seal and the sealing plate 174 together constitute the second seal of the pressure relief device 170, sealing the connection gap between the pressure plate 173 and the end cover 1112 and the upper end of the pressure plate 173 simultaneously, providing redundant safety protection for the transformer bushing 100. If the first sealing structure is damaged, the second sealing structure can immediately serve as a backup sealing structure, significantly improving the safety and reliability of the transformer bushing 100.

[0046] The waterproof cap 176 has a cup-shaped structure. The waterproof cap 176 is completely covered by the fastening plate 175, the sealing plate 174 and the pressure plate 173 to prevent water vapor from entering the stepped hole 11121 from the connection between the pressure plate 173, the sealing plate 174 and the fastening plate 175, and then entering the inside of the transformer bushing 100. A second groove 11124 is provided on the end face of the end cap 1112 away from the cabinet body 1111. The second groove 11124 is an annular groove. The second groove 11124 is arranged around the stepped hole 11121, and the opening direction of the second groove 11124 is perpendicular to the end face of the end cap 1112 away from the cabinet body 1111. Thus, two annular groove surfaces are formed on the second groove 11124. The axial direction of the two annular groove surfaces coincides with the axial direction of the stepped hole 11121. The annular groove surface with a smaller annular size is defined as the inner annular groove surface 11125, and the annular groove surface with a larger annular size is defined as the outer annular groove surface 11126. The inner annular groove surface 11125 and the outer annular groove surface 11126 together constitute the annular second groove 11124.

[0047] The shortest distance between the axis of the stepped hole 11121 and the circular outer circumferential surface of the end cap 1112 is equal to the radius of the pressure plate 173. This ensures that when the pressure plate 173 is fixedly connected to the end cap 1112, the circular outer circumferential surface of the pressure plate 173 is tangent to the circular outer circumferential surface of the end cap 1112, preventing the pressure plate 173 from protruding from the outer circumferential surface of the end cap 1112, thus facilitating the covering of the waterproof cap 176. The diameter of the inner annular groove surface 11125 of the second groove 11124 is equal to the outer diameter of the pressure plate 173. Therefore, when the pressure plate 173 is fixedly connected to the end cap 1112, the outer circumferential surface of the pressure plate 173 is flush with the inner annular groove surface 11125 of the second groove 11124. Meanwhile, the inner diameter of the waterproof cap 176 is equal to the outer diameter of the pressure plate 173, so that the opening of the waterproof cap 176 can be tightly fitted and covered on the outer peripheral surface of the pressure plate 173, the outer peripheral surface of the sealing plate 174, and the outer peripheral surface of the fastening plate 175. When the waterproof cap 176 further abuts against the bottom surface of the second groove 11124, the waterproof cap 176 can simultaneously cover the outer peripheral surface of the pressure plate 173 and the inner annular groove surface 11125 of the second groove 11124, that is, the waterproof cap 176 can further cover the gap at the connection between the pressure plate 173 and the end cap 1112. The waterproof cap 176 is made of a rubber material with low mechanical strength, which is easy to push out when the internal pressure is too high, so as to achieve rapid pressure relief. For example, silicone rubber or other rubber materials are used. By applying adhesive to the inner wall of the waterproof cap 176, the waterproof cap 176 is sealed on the outer peripheral surface of the pressure plate 173, the outer peripheral surface of the sealing plate 174, the outer peripheral surface of the fastening plate 175, and part of the outer peripheral surface of the end cover 1112. This effectively prevents external moisture from entering the transformer bushing 100 from the connection between the pressure plate 173 and the end cover 1112, and ensures the long-term reliability of the equipment's insulation performance.

[0048] By setting up a pressure relief device 170, when the internal pressure of the transformer bushing 100 is too high, the pressure is released outward from the stepped hole 11121 on the end cover 1112, which pushes out the plug 171, pressure plate 173, sealing plate 174, fastening plate 175 and waterproof cap 176 in sequence, thereby realizing instantaneous pressure relief and avoiding damage to other components and connection structures of the transformer bushing 100. When the internal pressure of the transformer bushing 100 is too high but does not have a destructive effect on the pressure relief device 170, the pressure will slightly push up the plug 171 and release it outward from the opening in the center of the pressure plate 173. This will cause the sealing plate 174 and the waterproof cap 176 to bulge slightly in sequence, or cause the sealing plate 174 to rupture and the waterproof cap 176 to bulge slightly, thus achieving graded buffering of pressure. Alternatively, the sealing plate 174 may rupture and the waterproof cap 176 may be partially pushed out, thus achieving partial pressure release. In both cases, the bulging or pushing out of the waterproof cap 176 can be clearly observed. At this time, it is only necessary to manually remove the sealing plate 174 and the waterproof cap 176 to release the pressure and replace them.

[0049] The pressure relief device 170 of this application is a one-way valve structure with multiple repeated opening and automatic reset functions. Compared with a one-time pressure relief structure, it can avoid the problem of the entire transformer bushing 100 being scrapped due to misoperation during non-faulty times. The starting pressure of the pressure relief device 170 is 0.5MPa. That is, when the internal pressure of the transformer bushing 100 is greater than or equal to 0.5MPa, the pressure relief device 170 starts to relieve pressure, and when the internal pressure of the transformer bushing 100 is less than 0.5MPa, the pressure relief device 170 closes, thereby achieving long-term and repeated safety protection. Meanwhile, this pressure meets the requirements of GB / T 4109-2022 "Insulated bushings for alternating voltages above 1000 V" and IEC 60137-2017 "Insulated bushings for alternating voltages above 1000 V" regarding the internal pressure of 0.2 MPa for the transformer bushing sealing test. This prevents the transformer bushing 100 from being accidentally opened due to excessive internal pressure caused by excessively high ambient temperature during operation, and ensures the stable operation of the transformer bushing 100 under all operating conditions.

[0050] In one application scenario, a transformer bushing 100 equipped with the aforementioned pressure relief device 170 is used. When the internal pressure of the transformer bushing 100 is 0.55 MPa, this pressure value does not reach the destructive value of the pressure relief device 170. At this time, the pressure relief device 170 is activated to relieve pressure. Under the impact of the pressure and the force of the spring 172, the plug 171 moves away from the end cover 1112, and the excess pressure is discharged outward from the stepped hole 11121. The pressure plate 173, sealing plate 174, and fastening plate 175 on the pressure relief device 170 are not pushed out, but the waterproof cap 176 is quickly pushed out because it is only bonded by adhesive. Under this condition, only the waterproof cap 176 of the pressure relief device 170 needs to be replaced, and the rest of the structure can continue to be used, enabling the pressure relief device 170 to have the function of repeated opening and automatic reset. Compared to existing technologies that use explosion-proof discs for pressure relief, when the internal pressure reaches the activation pressure value of the explosion-proof disc, the disc will burst directly, requiring the entire transformer bushing to be replaced, resulting in higher maintenance costs.

[0051] In another embodiment, the pressure relief device 170 may not include the sealing plate 174 and the fastening plate 175. In this case, the pressure relief device 170 only includes the plug 171, the spring 172, the pressure plate 173, and the waterproof cap 176. The waterproof cap 176 is sleeved and installed on the outermost side of the pressure relief device 170, that is, sleeved on the pressure plate 173. At the same time, the waterproof cap 176 is sleeved and covers the outer peripheral surface of the pressure plate 173 and the inner annular groove surface 11125 of the second groove 11124. The specific structure of each component is as described above and will not be repeated. The difference lies in that the pressure plate 173 is directly fixed to the end cover 1112 using fasteners, and the waterproof cap 176 is directly and tightly fitted onto the outer circumferential surface of the pressure plate 173, further abutting against the bottom surface of the second groove 11124. This allows the waterproof cap 176 to simultaneously cover the outer circumferential surface of the pressure plate 173 and the inner annular groove surface 11125 of the second groove 11124, preventing moisture from entering the stepped hole 11121 from the connection between the pressure plate 173 and the end cover 1112, and subsequently into the transformer bushing 100. In this case, the pressure relief device 170 only has one seal, namely the sealing structure located between the plug 171 and the stepped hole 11121, which can also meet the sealing requirements of the transformer bushing 100 during normal operation.

[0052] In another embodiment, the pressure relief device 170 does not include a waterproof cap 176, and the end cap 1112 does not need to have a second groove 11124. For example, the pressure relief device 170 only includes a plug 171, a spring 172, and a pressure plate 173. The plug 171 is disposed in the stepped hole 11121, the spring 172 is sleeved on the plug 171, and the pressure plate 173 is directly fixed to the end cap 1112 after pressing against the spring 172 by fasteners; or the pressure relief device 170 only includes a plug 171, a spring 172, a pressure plate 173, a sealing plate 174, and fasteners. Plate 175 and plug 171 are disposed in stepped hole 11121. Spring 172 is sleeved on plug 171. Pressure plate 173 covers spring 172. Sealing plate 174 covers end face of pressure plate 173 away from end cover 1112. Fastening plate 175 covers end face of sealing plate 174 away from pressure plate 173. Fasteners are sequentially inserted through fastening plate 175, sealing plate 174 and pressure plate 173 to fix pressure plate 173, sealing plate 174 and fastening plate 175 to end cover 1112. The specific structure of each component is as described above and will not be repeated.

[0053] In this embodiment, a pressure relief device 170 is provided on the end cover 1112 of the oil tank 111. In other embodiments, two, three or more pressure relief devices 170 may be provided on the end cover 1112 of the oil tank 111. Of course, one or more pressure relief devices 170 may also be provided on the cabinet 1111 of the oil tank 111. The specific design is based on the needs and is not limited here.

[0054] See Figure 5 At least one pressure relief device 170 is provided on the intermediate flange 140. A stepped hole is provided on the side of the intermediate flange 140, and the pressure relief device 170 is connected to the stepped hole. The specific structure of the pressure relief device 170 is the same as described above and will not be repeated. By providing the pressure relief device 170 on the intermediate flange 140, when an arc fault occurs inside the transformer bushing 100, the generated pressure will first be partially discharged through the pressure relief device 170 at the intermediate flange 140, further preventing damage to the insulating tube 151 in the oil. Two, three, or more pressure relief devices 170 can also be provided on the intermediate flange 140; no limitation is made here.

[0055] By installing at least one pressure relief device 170 on the intermediate flange 140 and the oil conservator 111 respectively, that is, by providing at least two pressure relief structures on the transformer bushing 100, the pressure relief device 170 on the intermediate flange 140 is the first pressure relief device, and the pressure relief device 170 on the oil conservator 111 is the second pressure relief device. When an arc fault occurs in the transformer bushing 100, the generated pressure will first be partially discharged through the first pressure relief device, achieving immediate and nearby pressure relief, effectively reducing the pressure peak, and thus prioritizing the protection of the oil-insulating tube 151 from damage. After the initial pressure relief, the residual pressure reaches the oil conservator 111 through the inner cavity of the composite insulator 130, and will concentrate its impact on the second pressure relief device, from which the residual pressure can then be discharged, avoiding direct high-voltage action that could damage the composite insulator 130 or the oil conservator 111. The above-mentioned dual pressure relief mechanism achieves segmented protection of the key insulating components of the transformer bushing 100, significantly improving the operational safety of the transformer bushing 100 under extreme fault conditions.

[0056] In one embodiment, an internal arcing test was conducted on three types of transformer bushings designed under the same voltage level and operating current. These three types include a traditional porcelain transformer bushing (Comparative Example 1), a composite transformer bushing without a pressure relief device (Comparative Example 2), and a composite transformer bushing with pressure relief devices in both the oil conservator and the intermediate flange (embodiment of this application). At the same time, the fault point on each type of transformer bushing was set in the oil-insulated tube inserted into the transformer, and the same fault current was applied for the same duration. The test results of the embodiment of this application and the different comparative examples are shown in Table 1.

[0057] Table 1 Comparison of Fault Tests

[0058] Group Transformer bushing type Test results Comparative Example 1 Traditional porcelain transformer bushings The porcelain sleeve cavity ruptured, the sealing structure failed, the porcelain sleeve disintegrated, oil and gas were ejected, and a deflagration occurred accompanied by sparks. Comparative Example 2 Composite transformer bushings without pressure relief devices Pressure was released from the top end cap of the oil conservator, causing the end cap to detach and the wiring terminals to come loose. The bushing did not explode or shatter. Examples of this application Composite transformer bushings with pressure relief devices in both the oil conservator and intermediate flange. The pressure relief devices at the intermediate flange and the oil conservator cover were activated to release pressure. The bushing did not explode or shatter; its overall integrity remained good. The end cover of the oil conservator did not detach, and the riser connecting to the transformer bushing was intact.

[0059] As shown in Table 1, when the internal pressure reaches a certain value, the porcelain bushing cavity in Comparative Example 1 ruptures, the sealing structure fails, and a serious safety accident occurs. In Comparative Example 2, the main structure is not damaged, but the oil conservator end cover and wiring terminals detach. In contrast, in the embodiment of this application, when the internal pressure reaches the same value, the pressure relief devices 170 on the intermediate flange 140 and end cover 1112 are activated in time to release the pressure, ensuring that none of the components are damaged and maintaining the integrity of the overall transformer bushing structure. This experimental result proves that this application, through a unique dual pressure relief device and a design that disrupts the internal pressure gradient, successfully solves the problems of easy breakage and explosion during arc faults, difficult maintenance, and easy displacement and oil leakage during operation of traditional porcelain bushings, achieving a balance between controllable release of fault pressure and structural safety.

[0060] The transformer bushing of this application uses a fiber-reinforced resin composite insulating tube and an integrally injection-molded high-temperature vulcanized silicone rubber shed. The insulating tube, through its winding angle design, possesses excellent mechanical strength and toughness, preventing explosion even under extreme conditions of excessive internal pressure. Furthermore, the oil-insulated tube employs a large-angle winding design or a combination of small-angle winding and circumferential winding, allowing it to withstand greater internal pressure without damage. Compared to traditional porcelain bushings, this design avoids the risk of explosion due to arcing faults within the transformer or transformer bushing, thus preventing serious secondary injuries from flying porcelain fragments.

[0061] All structures of the transformer bushing are fixedly connected using an adhesive bonding process, and the adhesive bonding strength is set to be greater than the destructive strength of each structure itself. This prioritizes the strength of the connection structure, ensuring that the transformer bushing will not experience circumferential or axial displacement under abnormal stress, thus guaranteeing structural integrity and preventing transformer oil leakage and accidents caused by damage to the transformer bushing.

[0062] When the pressure inside the transformer bushing is high enough that the pressure relief device cannot completely release it, the components will not experience circumferential or axial displacement when subjected to abnormal stress inside the transformer bushing. This is because the connections between the oil conservator and the composite insulator, the composite insulator and the intermediate flange, the intermediate flange and the oil-insulated pipe, and the oil-insulated pipe and the base are all fixed with adhesive. Furthermore, by setting a reasonable internal pressure gradient between the components of the transformer bushing, i.e., the internal pressure of the oil-insulated pipe > the internal pressure of the oil conservator ≈ the internal pressure of the intermediate flange > the internal pressure of the composite insulator, priority is given to ensuring that the oil-insulated pipe does not break, followed by the oil conservator and the intermediate flange, and finally the composite insulator. This ensures the structural integrity of the transformer bushing and prevents transformer oil leakage due to damage to the transformer bushing.

[0063] Furthermore, by installing at least one pressure relief device on the transformer bushing, such as when at least one pressure relief device is installed on the oil conservator, if an arcing fault occurs in the transformer bushing in the oil, the resulting pressure will first be discharged through the pressure relief device, preventing damage to the transformer bushing components. Further, when at least one pressure relief device is installed on both the oil conservator and the intermediate flange, if an arcing fault occurs in the transformer bushing, part of the resulting pressure will first be discharged through the pressure relief device on the intermediate flange, preventing damage to the insulating pipe in the oil. The remaining pressure will be discharged through the pressure relief device on the oil conservator, preventing damage to the composite insulator and the oil conservator. This dual pressure relief mechanism achieves segmented protection of the key insulating components of the transformer bushing, significantly improving the operational safety of the transformer bushing under extreme fault conditions.

[0064] The pressure relief device in this application features two sealing structures. The first seal, located between the plug and the stepped hole, is the main sealing structure of the pressure relief device, preventing external ambient air from communicating with the inner cavity of the oil conservator due to the stepped hole during normal operation of the transformer bushing. The second seal is located at the connection between the pressure plate and the end cover, sealing simultaneously from the connection gap between the pressure plate and the end cover and the upper end of the pressure plate. This provides redundant safety protection for the transformer bushing. When the first sealing structure is damaged, the second sealing structure can immediately serve as a backup sealing structure, significantly improving the safety and reliability of the transformer bushing.

[0065] The technical content and features of this application have been disclosed above. However, it is understood that, based on the inventive concept of this application, those skilled in the art can make various changes and improvements to the above-described structure and materials, including combinations of the technical features disclosed or claimed herein, and explicitly including other combinations of these features. All such modifications and / or combinations fall within the technical field to which this application pertains and are within the scope of protection of the claims of this application.

Claims

1. A transformer bushing, characterized in that, It includes a conductive rod and a head assembly, a composite insulator, an intermediate flange, and a tail assembly that are fixedly connected in sequence. The conductive rod passes through the head assembly, the composite insulator, the intermediate flange, and the tail assembly in sequence. The oil storage tank of the head assembly includes a cabinet body and an end cover connected to each other, and at least one pressure relief device is provided on the end cover. The second end of the cabinet is fixed to the first end of the composite insulator, the second end of the composite insulator is fixed to the first end of the intermediate flange, and the second end of the intermediate flange is fixed to the first end of the oil-insulating tube of the tail assembly by adhesive. The internal pressure at which the oil tank breaks down is greater than the internal pressure at which the composite insulator breaks down but less than the internal pressure at which the insulating tube in the oil breaks down.

2. The transformer bushing as described in claim 1, characterized in that, The composite insulator includes an insulating tube, which is made by impregnating fibers with resin and then winding and curing them, with the winding angle of the fibers being 30° to 60°.

3. The transformer bushing as described in claim 2, characterized in that, The ratio of the adhesive height to the outer diameter of the insulating tube is in the range of 0.2 to 0.4, and / or, The ratio of the adhesive height of the oil-insulating tube to the outer diameter of the oil-insulating tube is in the range of 0.2 to 0.

4.

4. The transformer bushing as described in claim 1, characterized in that, The adhesive strength of the composite insulator is greater than the breaking strength of the composite insulator, and / or, The adhesive strength of the insulating tube in the oil is greater than the breaking strength of the insulating tube in the oil.

5. The transformer bushing as described in claim 1, characterized in that, The adhesive fixing is performed by filling with adhesive, and the filling gap of the adhesive is in the radial direction of the transformer bushing, ranging from 0.25 mm to 0.5 mm.

6. The transformer bushing as described in claim 1, characterized in that, The oil-insulating tube is made by impregnating fibers with resin and then winding and curing them. The winding angle of the fibers is greater than or equal to 70° and less than 90°.

7. The transformer bushing as described in claim 1, characterized in that, The oil-insulating tube is made by impregnating fibers with resin and then winding and curing them. The fibers form multiple insulating layers, and the multiple insulating layers include at least one circumferential winding layer and one inclined winding layer. The winding angle of the fibers in the circumferential winding layer is greater than or equal to 80° and less than 90°, and the winding angle of the fibers in the inclined winding layer is 30° to 60°.

8. The transformer bushing as described in claim 1, characterized in that, The thickness of the insulating tube in the oil is greater than the thickness of the insulating tube in the composite insulator.

9. The transformer bushing as described in claim 2, 6, or 7, characterized in that, The fiber is glass fiber or aramid fiber, and / or, The resin is epoxy resin or phenolic resin.

10. The transformer bushing as described in claim 1, characterized in that, The end cap is provided with a stepped hole. The pressure relief device includes a plug, a spring and a pressure plate. The plug is disposed in the stepped hole, the spring is sleeved on the plug, and the pressure plate presses down on the spring and is fixedly connected to the end cap.

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