An accident safety type transformer bushing and a design method thereof

Abstract

The application discloses an accident safety type transformer bushing and a design method thereof, and the mechanical strength of an air side insulator of the bushing is designed to be lower than that of an oil insulator, and the existing upper and lower porcelain bushings with the same mechanical strength are replaced, in the case of internal failure of the transformer bushing, the air side insulator is preferentially broken to release pressure, and the oil insulator is protected, so that the insulating oil of the transformer body is prevented from contacting the atmosphere through the bushing part, the accident is prevented from being expanded, and the technical problem that the existing oil paper capacitor type bushing is easy to cause the transformer body to catch fire and be burned after self combustion caused by the upper and lower porcelain bushings is solved, and the safe operation of the transformer is affected.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and in particular to an accident-safe transformer bushing and its design method. Background Technology

[0002] Power transformers are core assets of the power grid, playing a crucial role in voltage transformation, power transmission, and distribution within the power system. Faults in these transformers can lead to power outages or, in severe cases, explosions and fires threatening personal safety and property. Transformer bushings are another vital component, responsible for leading the transformer's internal windings out of the tank, while also providing insulation to the leads, carrying current, and offering mechanical support to the leads.

[0003] Currently, most high-voltage transformer bushings (above 66kV) are oil-paper capacitor bushings. This type of bushing mainly consists of an oil-paper capacitor core, upper porcelain bushing, lower porcelain bushing, mounting flange, oil conservator, and current transformer shielding cylinder. Insulating oil is filled between the oil-paper capacitor core and the porcelain bushing. The entire bushing is assembled as a single unit by a clamping system consisting of a coiled tube, a top spring, and a bottom nut. The bushing is installed on the transformer, with one end inserted into the transformer tank or riser, and the other end exposed to air. When an electric arc discharge occurs inside the bushing, the insulating oil vaporizes and decomposes at high temperature, producing a large amount of gas, causing a rapid increase in internal pressure, which can lead to the rupture of the porcelain bushing. Once the porcelain bushing ruptures, firstly, the insulating oil inside the bushing will come into contact with the outside air and ignite. Secondly, due to the rupture of the porcelain bushing, the overall clamping structure of the bushing is destroyed, and transformer oil will spray out from the bushing installation position and come into contact with the outside air. If the bushing is already on fire, the transformer oil will also be ignited, expanding the fault area from the bushing to the transformer body, which is detrimental to the safe operation of the transformer. Therefore, it is necessary to take measures to prevent the impact of a bushing rupture leading to a fire and explosion from spreading to the transformer body and causing it to burn out. The current solution is to replace oil-paper capacitor bushings with dry bushings. However, using dry bushings has limitations due to long manufacturing cycles, high costs, and the lack of self-recovery properties in the internal insulation of the capacitor core. Summary of the Invention

[0004] This invention provides an accident-safe transformer bushing and its design method, which solves the technical problem that the existing oil-paper capacitor bushings, when the upper and lower porcelain bushings malfunction, can easily ignite and explode, further causing the transformer body to catch fire and be burned, thus affecting the safe operation of the transformer.

[0005] In view of this, the first aspect of the present invention provides an accident-safe transformer bushing, including an oil conservator, insulating oil, capacitor core, mounting flange, and also includes an air-side insulator and an oil-in-soil insulator;

[0006] The oil conservator, air-side insulator, mounting flange, and oil-immersed insulator are connected sequentially from top to bottom, with insulating oil filling the inside of the transformer bushing;

[0007] The mechanical strength of air-insulators is lower than that of oil-insulators.

[0008] Optionally, the air-side insulator is a hollow composite insulator. The internal skeleton of the hollow composite insulator is a tube made of glass fiber impregnated with epoxy material. The inside of the tube is grooved. The outside of the hollow composite insulator is a silicone rubber shed. The upper part of the tube is equipped with an upper flange and the lower part is equipped with a lower flange. The silicone rubber shed is located between the upper flange and the lower flange.

[0009] The oil-insulated insulator is an epoxy resin insulator.

[0010] Optionally, the epoxy resin insulator has a nut with a multi-segment arc structure embedded inside. The nut has internal threads machined inside for mating with the rolled tube of the capacitor core. The nut also has a sealing groove inside for sealing the gap between the rolled tube and the nut.

[0011] Optionally, the mounting flange includes a connecting flange and a current transformer shielding cylinder, the connecting flange and the current transformer shielding cylinder are welded together, the connecting flange is connected to the lower flange, and the current transformer shielding cylinder is glued to the oil insulator.

[0012] Optionally, it also includes a characteristic gas detection alarm device;

[0013] The characteristic gas detection alarm device is installed on the oil tank.

[0014] Optionally, the characteristic gas detection alarm device includes a gas sensor, a main control module, and an energy harvesting module;

[0015] The energy harvesting module can be a photovoltaic power module or a wireless charging module;

[0016] The drive module is connected to the gas sensor and the main control module respectively, and the gas sensor is connected to the main control module.

[0017] The main control module includes a detection circuit and an alarm circuit. The detection circuit is used to analyze the gas detection data of the gas sensor and determine whether to trigger the alarm circuit based on the gas analysis results.

[0018] Optionally, the capacitor core includes a wound tube and an oil-paper insulating capacitor layer. The wound tube is a hollow aluminum alloy tube, and the oil-paper insulating capacitor layer is wound with the wound tube as a skeleton. After each oil-paper insulating capacitor layer of a certain thickness is wound, an aluminum foil is wound, and a capacitor is formed between two adjacent aluminum foil layers.

[0019] A second aspect of the present invention provides a design method for the fault-safe transformer bushing described in the first aspect of the present invention, comprising the following steps:

[0020] S1. When designing air-side insulators, design the air-side insulators according to the design parameters of the transformer bushings;

[0021] S2. When designing oil-insulated insulators, design the oil-insulated insulators according to the design parameters of the transformer bushings;

[0022] S3. Determine if the mechanical strength of the air-side insulator is lower than that of the oil-insulator. If so, design the transformer bushing based on the designed air-side and oil-insulators. If not, adjust the mechanical strength control parameter of the air-side insulator in the design parameters to reduce the mechanical strength of the air-side insulator and return to step S1, or adjust the mechanical strength control parameter of the oil-insulator in the design parameters to increase the mechanical strength of the oil-insulator and return to step S2.

[0023] Optionally, step S1 includes:

[0024] S1-1. Establish the geometric model of the hollow composite insulator based on the transformer bushing design parameters;

[0025] S1-2. Set the number of slots, slot shape, and slot size in the geometric model of the hollow composite insulator;

[0026] S1-3. Mesh the geometric model of the hollow composite insulator. The mesh size is 1 / 2 of the slot size.

[0027] S1-4. Apply bending load to the geometric model of the hollow composite insulator;

[0028] S1-5. Calculate the stress on the hollow composite insulator under bending load and determine whether the withstand strength of the hollow composite insulator under stress meets the requirements. If not, return to step S1-2. If yes, apply internal pressure load to the geometric model of the hollow composite insulator and calculate the stress on the hollow composite insulator under internal pressure load. If the withstand strength of the hollow composite insulator under internal pressure load meets the requirements, the design of the hollow composite insulator is completed. If it does not meet the requirements, return to step S1-2.

[0029] Optionally, when designing oil-insulated insulators, the electric field strength distribution characteristics of the nut are evaluated. This evaluation includes:

[0030] T1. According to the geometric model of the oil-filled part of the transformer bushing, the geometric model of the oil-filled part includes the capacitor core, the oil-filled insulator, the connecting flange, and the inner boundary of the transformer riser.

[0031] T2. Mesh the geometric model of the oil portion;

[0032] T3. Apply a high potential to the innermost plate of the capacitor core in the geometric model of the oil section, apply a zero potential to the connecting flange, the outermost plate and the inner boundary of the riser, and apply a linear potential to the line segment between the ends of the innermost plate and the outermost plate to simulate the capacitive voltage division of the capacitor core during operation.

[0033] T4. Design the external shape of the nut inside the oil insulator as a multi-segment arc structure, and use electric field calculation software to calculate the electric field strength of the nut in the oil under a certain voltage stress.

[0034] T5. Evaluate whether the electric field strength meets the requirements. If yes, complete the design of the insert nut for the oil insulator. If not, adjust the external shape of the nut inside the oil insulator to increase the radius of curvature of the electric field concentration area, and return to step T2.

[0035] As can be seen from the above technical solutions, the accident-safe transformer bushing provided by the present invention has the following advantages:

[0036] The accident-safe transformer bushing provided by this invention designs the mechanical strength of the air-side insulator to be lower than that of the oil-insulator, replacing the existing upper and lower porcelain bushings with the same mechanical strength. In the event of an internal fault in the transformer bushing, the air-side insulator will rupture and release pressure first, protecting the oil-insulator. This prevents the insulating oil of the transformer body from contacting the atmosphere through the bushing, thus preventing the accident from escalating. This solves the technical problem that existing oil-paper capacitor bushings, which use upper and lower porcelain bushings, are prone to self-ignition and explosion after a fault, which can further cause the transformer body to catch fire and be burned, affecting the safe operation of the transformer.

[0037] Meanwhile, the accident-safe transformer bushing provided by this invention is an improvement based on the oil-paper capacitor bushing, avoiding the technical problems of long manufacturing cycle, high cost, and lack of self-recovery of internal insulation of capacitor core that exist in the scheme of using dry bushing to replace oil-paper insulating bushing.

[0038] The accident-safe transformer bushing provided by this invention is equipped with a characteristic gas monitoring and alarm device on the oil conservator, which realizes the detection and alarm functions of characteristic gases generated by oil discharge and overheating, further improving the safety of transformer operation.

[0039] The accident-safe transformer bushing provided by this invention incorporates a nut as an insert into the epoxy resin insulator. The nut is designed with a multi-segment arc shape to achieve a uniform electric field and provide electric field shielding, eliminating the need for a dedicated shielding ball. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a half-sectional view of an accident-safe transformer bushing provided in an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of the structure of the air-side insulator of the accident-safe transformer bushing provided in an embodiment of the present invention;

[0043] Figure 3 This is a top view of the air-side insulator of the accident-safe transformer bushing provided in an embodiment of the present invention;

[0044] Figure 4 A schematic diagram of a half-section of the oil-insulated component of an accident-safe transformer bushing provided in this embodiment of the invention;

[0045] Figure 5 This is a flowchart illustrating a design method for an accident-safe transformer bushing provided in an embodiment of the present invention;

[0046] Figure 6 A schematic diagram of the air-side insulator design process provided in this embodiment of the invention;

[0047] Figure 7 This is a schematic diagram of the process for evaluating the electric field intensity distribution characteristics of an oil-filled insulator nut, as provided in an embodiment of the present invention.

[0048] Figure 8 This is a schematic diagram of the outline of the simulated electrode plate provided in an application example of the present invention;

[0049] Figure 9 This is a schematic diagram of the potential distribution of the oil-insulator portion provided in an application example of the present invention;

[0050] Figure 10 This is a schematic diagram of the surface electric field of the nut insert in the oil-insulator portion provided in an application example of the present invention;

[0051] Figure 11 This is a schematic diagram of the stress distribution of the air-side insulator provided in this invention under maximum internal pressure.

[0052] Figure 12 This is a schematic diagram showing the stress on the air-side insulator and the oil-side insulator when a pressure of 0.2 MPa is applied inside the bushing provided in this invention.

[0053] The attached figures are labeled as follows:

[0054] 100. Oil tank; 200. Insulating oil; 300. Air-side insulator; 301. Pipe; 302. Upper flange; 303. Silicone rubber shed; 304. Lower flange; 3011. Groove; 400. Capacitor core; 500. Mounting flange; 501. Connecting flange; 502. Current transformer shielding cylinder; 600. Oil-insulated insulator; 601. Insulator body; 602. Nut; 6021. Internal thread; 6022. Sealing groove; 700. Characteristic gas detection alarm device. Detailed Implementation

[0055] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] For easier understanding, please refer to Figure 1 The present invention provides an embodiment of an accident-safe transformer bushing, including an oil conservator 100, insulating oil 200, capacitor core 400, mounting flange 500, and also includes an air-side insulator 300 and an oil-in-oil insulator 600.

[0057] Oil conservator 100, air-side insulator 300, mounting flange 500 and oil-in-oil insulator 600 are connected sequentially from top to bottom, and insulating oil 200 is filled inside the transformer bushing;

[0058] The mechanical strength of air-side insulator 300 is lower than that of oil-insulator 600.

[0059] It should be noted that the oil conservator 100, as a component for storing insulating oil 200, ensures that the capacitor core 400 is always immersed in the insulating oil 200 at different temperatures. The insulating oil 200 serves as a cooling and insulating medium, filling the interior of the bushing.

[0060] In this invention, the mechanical strength of the air-side insulator 300 is designed to be lower than that of the oil-insulator 600, replacing the existing upper and lower porcelain bushings with the same mechanical strength. In the event of an internal fault in the transformer bushing, the air-side insulator 300 will rupture and release pressure first, protecting the oil-insulator 600. This prevents the insulating oil 200 of the transformer body from contacting the atmosphere through the bushing, thus preventing the accident from escalating. This invention solves the technical problem that existing oil-paper capacitor bushings, which use upper and lower porcelain bushings, are prone to self-ignition and explosion after a fault, which can easily lead to the transformer body catching fire and being burned, affecting the safe operation of the transformer.

[0061] In one embodiment, see Figures 2 to 4 The air-side insulator 300 of the accident-safe transformer bushing provided in this invention is a hollow composite insulator. The internal skeleton of the hollow composite insulator is a tube 301 made of glass fiber impregnated with epoxy material. The tube 301 has grooves 3011 inside, and the shape, size and number of grooves 3011 are determined by mechanical strength calculations. The outside of the hollow composite insulator is a silicone rubber shed 303. An upper flange 302 is arranged at the top of the tube 301, and a lower flange 304 is arranged at the bottom. The silicone rubber shed 303 is located between the upper flange 302 and the lower flange 304. The oil insulator 600 is an epoxy resin insulator. Specifically, the groove treatment inside the hollow composite insulator tube 301 can reduce the mechanical strength of the tube 301. In the event of an internal fault, the air-side insulator 300 will break first to release pressure, protecting the oil insulator 600. The oil-insulator 600 is cast from epoxy resin and has a multi-segment arc-shaped nut 602 embedded inside. The nut 602 has internal threads 6021 machined inside for mating with the rolled tube of the capacitor core 400. The nut 602 also has a sealing groove 6022 inside, which seals the gap between the rolled tube and the nut 602, preventing the leakage of insulating oil 200 from the bushing. The nut 602 is made of metal, preferably aluminum alloy. The thickness of the insulator body 601 of the oil-insulator 600 is determined by mechanical strength requirements; specifically, the mechanical strength of the insulator body 601 of the oil-insulator 600 must be higher than that of the slotted tube 301 of the hollow composite insulator. The multi-segment arc-shaped external shape of the nut 602 helps to uniformly shape the electric field; the specific arc is determined by electric field calculations, thus eliminating the need for a dedicated shielding ball.

[0062] Mounting flange 500 includes connecting flange 501 and current transformer shielding cylinder 502. Connecting flange 501 and current transformer shielding cylinder 502 are welded together. Connecting flange 501 is connected to lower flange 304, and current transformer shielding cylinder 502 is glued to oil insulator 600. Mounting flange 500 is made of aluminum and is used for the mechanical connection between the bushing and the transformer. Since connecting flange 501 is at the same potential as the transformer casing (i.e., connecting flange 501 is at ground potential), current transformer shielding cylinder 502 is also at ground potential. Therefore, current transformer shielding cylinder 502 can provide electric field shielding for the bushing current transformer. The length of current transformer shielding cylinder 502 is determined by the axial dimension of the current transformer.

[0063] The capacitor core 400 includes a wound tube and an oil-paper insulating capacitor layer. The wound tube is a hollow aluminum alloy tube. The oil-paper insulating capacitor layer is wound with the wound tube as the skeleton. After each oil-paper insulating capacitor layer of a certain thickness is wound, an aluminum foil is wound. A capacitor is formed between two adjacent aluminum foil layers. The number of aluminum foil layers and the size of the capacitor core 400 are related to the voltage rating of the bushing.

[0064] The accident-safe transformer bushing provided in this invention is also equipped with a characteristic gas detection alarm device 700. This device 700 is installed on the oil conservator 100 and is used to detect characteristic gases in the gas above the oil level in the oil conservator 100. When the characteristic gas exceeds a specified value, an alarm is triggered, allowing for early detection of potential faults and prompting relevant personnel to take preventative measures. Specifically, the characteristic gas detection alarm device 700 includes a gas sensor, a main control module, and an energy harvesting module. The energy harvesting module is a photovoltaic power module or a wireless charging module. The drive module is connected to both the gas sensor and the main control module. The gas sensor is connected to the main control module, which includes a detection circuit and an alarm circuit. The detection circuit analyzes the gas detection data from the gas sensor and determines whether to trigger the alarm circuit based on the gas analysis results. The gas sensor converts the concentration of characteristic gases (such as hydrogen, acetylene, methane, etc., gases generated by oil discharge or overheating) above the oil level in the oil conservator 100 into an electrical signal. The detection circuit processes this electrical signal, and once the characteristic gas exceeds a specified value, the alarm circuit is triggered. The alarm can be an audible or visual alarm. The energy harvesting module provides power to the entire characteristic gas detection alarm device 700. Since the oil tank 100 is at a high potential, it cannot be directly powered by a general low-voltage power supply. Photovoltaic or wireless charging technology should be selected for power supply.

[0065] For easier understanding, please refer to Figure 5 This invention provides an embodiment of a design method for an accident-safe transformer bushing, comprising:

[0066] Step S1: When designing the air-side insulator 300, design the air-side insulator 300 according to the design parameters of the transformer bushing.

[0067] It should be noted that in the design of transformer bushings, after determining the target mechanical strength requirements of the air-side insulator 300, the air-side insulator 300 is designed according to the design parameters of the transformer bushing.

[0068] Step S2: When designing the oil-immersed insulator 600, design the oil-immersed insulator 600 according to the design parameters of the transformer bushing.

[0069] It should be noted that in the design of transformer bushings, after determining the target mechanical strength requirements of the oil-insulated 600, the oil-insulated 600 is designed according to the design parameters of the transformer bushing.

[0070] Step S3: Determine if the mechanical strength of the air-side insulator 300 is lower than that of the oil-insulator 600. If so, design the transformer bushing according to the designed air-side insulator 300 and oil-insulator 600. If not, adjust the mechanical strength control parameter of the air-side insulator 300 in the design parameters to reduce the mechanical strength of the air-side insulator 300 and return to step S1, or adjust the mechanical strength control parameter of the oil-insulator 600 in the design parameters to increase the mechanical strength of the oil-insulator 600 and return to step S2.

[0071] It should be noted that after designing the air-side insulator 300 and the oil-insulator 600, their mechanical strength is checked. If the mechanical strength of the air-side insulator 300 is lower than that of the oil-insulator 600, the transformer bushing is designed based on the designed air-side insulator 300 and oil-insulator 600. If not, the mechanical strength control parameter of the air-side insulator 300 in the design parameters is adjusted to reduce its mechanical strength, and the process returns to step S1. Alternatively, the mechanical strength control parameter of the oil-insulator 600 in the design parameters is adjusted to increase its mechanical strength, and the process returns to step S2. The mechanical strength control parameter of the air-side insulator 300 is the number of slots inside the tube 301. The mechanical strength control parameter of the oil-insulator 600 is the thickness of the insulator body 601 of the oil-insulator 600.

[0072] In one embodiment, such as Figure 6 As shown, the specific design process of the air-side insulator 300 is as follows:

[0073] Step S1-1: Establish the geometric model of the hollow composite insulator based on the transformer bushing design parameters. Since the silicone rubber shed 303 has little impact on mechanical strength, it can be omitted, retaining only the tube 301, upper flange 302, and lower flange 304 as the internal skeleton. The upper flange 302 and lower flange 304 can be appropriately simplified, for example, by adding a sealing groove 6022, but features that significantly affect mechanical strength must be retained, such as reinforcing ribs.

[0074] Step S1-2: Set the number of slots, slot shape, and slot size in the geometric model of the hollow composite insulator.

[0075] Step S1-3: Mesh the geometric model of the hollow composite insulator. The mesh size is 1 / 2 of the slot size.

[0076] Step S1-4: Apply a bending load to the geometric model of the hollow composite insulator. Apply a tensile load to the head of the hollow composite insulator on the geometric model established in step S1-3. The direction of the load is perpendicular to the axis of the hollow composite insulator and also perpendicular to the axis of the slot. The load is a static force, and the magnitude of the force is determined according to the design value of the bushing and the specifications of the hollow composite insulator.

[0077] Step S1-5: Calculate the stress on the hollow composite insulator under bending load, and determine whether the withstand strength of the hollow composite insulator under stress meets the requirements. If not, return to step S1-2. If yes, apply internal pressure load to the geometric model of the hollow composite insulator, calculate the stress on the hollow composite insulator under internal pressure load. If the withstand strength of the hollow composite insulator under internal pressure load meets the requirements, the design of the hollow composite insulator is completed. If it does not meet the requirements, return to step S1-2.

[0078] In one embodiment, such as Figure 7 As shown, in the design process of the oil-insulator 600, the shape of the insert nut 602 plays a key role in the electric field distribution of the bushing oil portion. Therefore, it is necessary to evaluate its electric field distribution characteristics during the design process. The specific procedure is as follows:

[0079] T1. Based on the geometric model of the oil-immersed portion of the transformer bushing, which includes the capacitor core 400, the oil-immersed insulator 600, the connecting flange 501, and the inner boundary of the transformer riser, the calculation can use a two-dimensional model, including the rolled tube, capacitor core 400, oil-immersed insulator 600, flange, and the inner boundary of the transformer riser. The capacitor core 400, in addition to its core outline, needs to retain the innermost and outermost plates, and a line segment is drawn between the ends of the two plates to simulate their outlines. After the model is completed, material properties are assigned to different components.

[0080] T2. Mesh the geometric model of the oil-filled section. Local mesh refinement can be performed on key areas of interest, such as insert attachments, ensuring that the mesh size increases gradually; generally, a circular arc should have at least 10 meshes.

[0081] T3. In the geometric model of the oil section, a high potential is applied to the innermost plate of the capacitor core 400, and a zero potential is applied to the connecting flange 501, the outermost plate, and the inner boundary of the riser. A linear potential is applied to the line segment between the ends of the innermost and outermost plates to simulate the capacitive voltage division of the capacitor core during operation. A high potential is applied to the innermost plate, with the potential value being the highest operating voltage of the bushing relative to ground. A zero potential is applied to the connecting flange 501, the outermost plate, and the boundary of the riser. A linear potential is applied to the line segment between the ends of the two plates (i.e., the innermost and outermost plates), meaning the potential linearly decreases from high potential to zero potential along the length of the line segment from the starting point (end of the innermost plate) to the ending point (end of the outermost plate), simulating the capacitive voltage division of the capacitor core 400 during operation. The advantage of this modeling method is that it eliminates the need to build intermediate plates, reducing the computational load.

[0082] T4. The external shape of the nut 602 inside the oil insulator 600 is a multi-segment arc structure. Use electric field calculation software to calculate the electric field strength of the oil portion of the nut 602 under a certain voltage stress.

[0083] T5. Evaluate whether the electric field strength meets the requirements. If yes, complete the design of the oil-insulator 600. If not, adjust the external shape of the nut 602 inside the oil-insulator 600 to increase the radius of curvature of the electric field concentration area, and return to step T2. If the electric field strength does not meet the requirements, modify the shape design of the nut 602 to increase the radius of curvature of the electric field concentration area. Return to step T2 again; if the electric field strength meets the requirements, the electric field verification of the oil-insulator 600 is complete.

[0084] This invention takes the design of a 126kV / 800A accident-safe transformer bushing as an example. The bushing design process is as follows:

[0085] Step 1: Determine the bushing insulation level as the highest operating phase-to-ground voltage. Lightning impulse withstand voltage 550kV, rated current 800A, current transformer length 500mm.

[0086] Step 2: Design the air-side dry arc distance, oil-side dry arc distance, and grounding section length. Based on the insulation level, select an air-side dry arc distance of 1050mm and an oil-side dry arc distance of 250mm. Based on the current transformer length, select a total grounding section length of 500 + 100 + 50 = 650mm.

[0087] Step 3: Design the capacitor core 400. Based on the rated current, select an inner diameter of 36mm and a thickness of 3mm for the rolled tube, resulting in an outer diameter of 42mm. Then, considering the length of the grounding section, the outermost electrode length is greater than the grounding section length, so select an outermost electrode length of 650 + 30 + 1050 * 0.1 = 785mm. Based on the outer diameter of the rolled tube, the diameter of the innermost electrode is greater than the outer diameter of the rolled tube, so select a diameter of 42 + 2 = 44mm. Select 28 electrode layers based on the insulation level. Using the equal margin method based on the above parameters, design the radius, length, and step length of each electrode layer.

[0088] Step 4: Design the shape of the nut 602 of the oil insulator 600.

[0089] Step 4.1: Establish the geometric model of the oil-filled portion of the bushing. Due to the axisymmetric structure of the bushing, a two-dimensional model can be used for calculation. The modeling includes the rolled tube, capacitor core 400, oil-filled insulator 600, flange, and the inner boundary of the transformer riser. For capacitor core 400, in addition to the core outline, the innermost and outermost plates need to be retained. A line segment is drawn between the ends of the two plates to simulate the plate outline, such as... Figure 8 As shown. After the model is drawn, material properties are assigned to different components: the capacitor core 400 is made of oil-impregnated paper, the current transformer shielding cylinder 502, the rolled tube, and the bottom nut 602 insert are made of aluminum alloy, the oil-insulated insulator 600 is made of epoxy resin, and the space between the riser cavity, the capacitor core 400, and the oil-insulated insulator 600 is made of insulating oil 200.

[0090] Step 4.2: Divide the grid and refine the local grid for key areas of interest, such as insert attachments. Ensure that the grid size increases gradually. Generally, an arc should have at least 10 grids.

[0091] Step 4.3: Apply excitation and boundary conditions, and apply the highest operating voltage to the innermost electrode. Zero potential is applied to the connecting flange 501, the outermost electrode plate, and the boundary of the riser. A linear potential is applied to the line segment at the ends of the two electrodes, that is, the potential decreases linearly from high potential to zero potential along the length of the line segment from the starting point (end of the innermost electrode plate) to the ending point (end of the outermost electrode plate), simulating the capacitance distribution of the capacitor core 400 under the operating voltage.

[0092] Step 4.4: Calculate the electric field distribution, check the equipotential lines, and confirm that the calculation results meet the loading and boundary conditions, such as... Figure 9 As shown. Examine the electric field distribution. Based on the electric field withstand strength of the oil-insulated insulator (600) and insulating oil (200), assess whether the electric field distribution meets the requirements. Figure 10 The electric field on the insert surface is 2.68 kV / mm, which meets the 3 kV / mm control value, so we can proceed to the next step.

[0093] Step 5: Slotting design of air insulator tube 301.

[0094] Step 5.1: Establish the geometric model of the hollow composite insulator. Since the insulator is no longer axisymmetric after slotting, a three-dimensional model is required. The silicone rubber shed 303 is omitted, while the tube 301, upper flange 302, and lower flange 304 are retained. The upper and lower flanges can be appropriately simplified, for example, by adding a sealing groove 6022, but features that significantly affect mechanical strength, such as reinforcing ribs, must be retained.

[0095] Step 5.2: Set the number of slots, the shape of the slots, and the size of the slots in the pipe 301. Two slots are symmetrically cut on the pipe. The slots are semi-circular and the depth of the slots is half the thickness of the pipe 301.

[0096] Step 5.3: Perform mesh generation. The mesh size is generally set to 1 / 2 of the slot size.

[0097] Step 5.4: Apply a bending load. Using the model established in Step 3, apply a tensile load to the insulator head. The load direction is perpendicular to the insulator axis and also perpendicular to the slot axis. The load is static, and its magnitude is determined according to the bushing design values ​​and the specifications for hollow composite insulators. Here, according to the hollow composite insulator standard, a load of 2.5 MML (maximum mechanical load) is applied in the type test. The cantilever withstand capability of the 126kV / 800A bushing is specified according to bushing standard GB / T 4109.

[0098] Step 5.5: Calculate the stress on the hollow composite insulator under bending load. Evaluate whether the requirements are met based on the material strength of tube 301, upper flange 302 and lower flange 304. If the requirements are not met, return to step 2. If the strength requirements are met, proceed to the internal pressure calculation.

[0099] Step 5.6: Apply internal pressure load. In the model established in Step 3, apply a static pressure to the inside of tube 301. The magnitude of the pressure is determined according to the design value of the bushing and the standard specifications for hollow composite insulators. This bushing is an oil-impregnated paper bushing, and the maximum operating pressure MSP is 0.1 MPa. The maximum internal pressure SIP specified for the internal pressure type test of hollow composite insulators is 2.5 times MSP, i.e., 0.4 MPa.

[0100] Step 5.7: Calculate the stress distribution of the slotted insulator under the maximum internal pressure (SIP). The results are as follows: Figure 11 As shown, the maximum stress occurs in the groove, with a maximum value of 8.07 MPa, which meets the control value requirement of 10 MPa, and we can proceed to the next step of the design process.

[0101] Step 6: Verify that the mechanical strength of the entire bushing meets expectations. According to the bushing standard, the bushing needs to be subjected to an internal pressure of maximum operating pressure + 0.1 MPa when it leaves the factory. Calculate the stress on the air-side insulator 300 and the oil-filled insulator 600 when a pressure of 0.2 MPa is applied inside the bushing. The results are as follows. Figure 12 As shown, the maximum stress occurs at the slotted portion of the air-side insulator 300, with a stress value of 4 MPa, while the maximum stress of the oil-insulator 600 is only 2 MPa, satisfying the strength matching relationship between the air-side insulator 300 and the oil-insulator 600. The entire bushing design process is now complete.

[0102] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An accident-safe transformer bushing, comprising an oil conservator, insulating oil, capacitor core, and mounting flange, characterized in that, This also includes air-side insulators and oil-insulators; The oil conservator, air-side insulator, mounting flange, and oil-immersed insulator are connected sequentially from top to bottom, with insulating oil filling the inside of the transformer bushing; The mechanical strength of air-insulators is lower than that of oil-insulators. The air-side insulator is a hollow composite insulator. The internal skeleton of the hollow composite insulator is a tube made of glass fiber impregnated with epoxy material. The inside of the tube is grooved. The outside of the hollow composite insulator is a silicone rubber shed. The upper part of the tube is equipped with an upper flange and the lower part is equipped with a lower flange. The silicone rubber shed is located between the upper flange and the lower flange. The oil-insulated insulator is an epoxy resin insulator.

2. The accident-safe transformer bushing according to claim 1, characterized in that, The epoxy resin insulator has a nut with a multi-segment arc structure embedded inside. The nut has internal threads machined inside for mating with the rolled tube of the capacitor core. The nut also has a sealing groove inside to seal the gap between the rolled tube and the nut.

3. The accident-safe transformer bushing according to claim 1, characterized in that, The mounting flange includes a connecting flange and a current transformer shield. The connecting flange and the current transformer shield are welded together. The connecting flange is connected to the lower flange. The current transformer shield is glued to the oil insulator.

4. The accident-safe transformer bushing according to claim 1, characterized in that, It also includes a characteristic gas detection alarm device; The characteristic gas detection alarm device is installed on the oil tank.

5. The accident-safe transformer bushing according to claim 4, characterized in that, The characteristic gas detection alarm device includes a gas sensor, a main control module, and an energy harvesting module; The energy harvesting module can be a photovoltaic power module or a wireless charging module; The energy harvesting module is connected to both the gas sensor and the main control module, and the gas sensor is connected to the main control module. The main control module includes a detection circuit and an alarm circuit. The detection circuit is used to analyze the gas detection data of the gas sensor and determine whether to trigger the alarm circuit based on the gas analysis results.

6. The accident-safe transformer bushing according to claim 1, characterized in that, The capacitor core consists of a wound tube and an oil-paper insulating capacitor layer. The wound tube is a hollow aluminum alloy tube. The oil-paper insulating capacitor layer is wound with the wound tube as the skeleton. After each oil-paper insulating capacitor layer of a certain thickness is wound, an aluminum foil is wound. A capacitor is formed between two adjacent aluminum foil layers.

7. A design method for an accident-safe transformer bushing applied to any one of claims 1-6, characterized in that, include: S1. When designing air-side insulators, design the air-side insulators according to the design parameters of the transformer bushings; S2. When designing oil-insulated insulators, design the oil-insulated insulators according to the design parameters of the transformer bushings; S3. Determine whether the mechanical strength of the air-side insulator is lower than that of the oil-insulator. If yes, design the transformer bushing according to the designed air-side and oil-insulators. If no, adjust the mechanical strength control parameter of the air-side insulator in the design parameters to reduce the mechanical strength of the air-side insulator and return to step S1, or adjust the mechanical strength control parameter of the oil-insulator in the design parameters to increase the mechanical strength of the oil-insulator and return to step S2.

8. The design method for an accident-safe transformer bushing according to claim 7, characterized in that, Step S1 includes: S1-1. Establish the geometric model of the hollow composite insulator based on the transformer bushing design parameters; S1-2. Set the number of slots, slot shape, and slot size in the geometric model of the hollow composite insulator; S1-3. Mesh the geometric model of the hollow composite insulator. The mesh size is 1 / 2 of the slot size. S1-4. Apply bending load to the geometric model of the hollow composite insulator; S1-5. Calculate the stress on the hollow composite insulator under bending load and determine whether the withstand strength of the hollow composite insulator under stress meets the requirements. If not, return to step S1-2. If yes, apply internal pressure load to the geometric model of the hollow composite insulator and calculate the stress on the hollow composite insulator under internal pressure load. If the withstand strength of the hollow composite insulator under internal pressure load meets the requirements, the design of the hollow composite insulator is completed. If it does not meet the requirements, return to step S1-2.

9. The design method for an accident-safe transformer bushing according to claim 7, characterized in that, When designing oil-insulated insulators, the electric field intensity distribution characteristics of the nut are evaluated. This evaluation includes: T1. Establish the geometric model of the oil-filled portion of the transformer bushing. The geometric model of the oil-filled portion includes the capacitor core, the oil-filled insulator, the connecting flange, and the inner boundary of the transformer riser. T2. Mesh the geometric model of the oil portion; T3. Apply a high potential to the innermost plate of the capacitor core in the geometric model of the oil section, apply a zero potential to the connecting flange, the outermost plate and the inner boundary of the riser, and apply a linear potential to the line segment between the ends of the innermost plate and the outermost plate to simulate the capacitive voltage division of the capacitor core during operation. T4. Design the external shape of the nut inside the oil insulator as a multi-segment arc structure, and use electric field calculation software to calculate the electric field strength of the nut in the oil under a certain voltage stress. T5. Evaluate whether the electric field strength meets the requirements. If yes, complete the design of the insert nut for the oil insulator. If not, adjust the external shape of the nut inside the oil insulator to increase the radius of curvature of the electric field concentration area, and return to step T2.

Images