Explosion-proof top cover, oil chamber structure and top cover verification method for on-load tap changers

Abstract

This invention provides an explosion-proof top cover, oil chamber structure, and a method for verifying the structural strength of an on-load tap changer. The top cover includes a top cover body; wherein the top cover body has a ring of small bolt holes arranged in a circular pattern, and a plurality of spaced connecting plates extend outward along the outer edge of the top cover body in the circumferential direction, each connecting plate having a large bolt hole; a plurality of radial reinforcing ribs are provided at the connection points between the top cover body and each connecting plate, each radial reinforcing rib extending outward from the center of the top cover body. This invention achieves radial expansion by extending connecting plates along the outer edge of the top cover body; it forms a double-layer bolted connection structure through the small and large bolt holes, realizing a double-layer bolted connection structure between the top cover and the transfer flange or oil tank top cover, dispersing the load at a single bolt hole and reducing its strain value; and through the radial reinforcing ribs, it suppresses the tendency of the top cover's central part to bulge upward under fault impact pressure, achieving overall structural reinforcement of the top cover.

Description

Technical Field

[0001] This invention relates to the field of on-load tap changer technology for transformers, and more specifically, to an explosion-proof top cover, oil chamber structure, and a method for verifying the strength of the top cover structure for an on-load tap changer. Background Technology

[0002] On-load tap changers are an essential core component of UHV converter transformers. They can adjust the turns ratio by changing the number of turns in the voltage regulating winding without interrupting power. This requires strict adherence to the design sequence, completing eight consecutive switching actions within 100ms. The timing error between two adjacent switching actions must be less than 2ms. A single failed switching action can easily trigger a fault, generating a short-circuit current in the hundreds of kiloamperes. The short-circuit fault capacity is extremely high, which can lead to tearing of the tap changer's oil chamber, resulting in deflagration and fire.

[0003] According to failure case statistics, the product has experienced a failure where an internal short circuit in the on-load tap changer caused a fire in the converter transformer, resulting in serious losses. Fault simulation analysis shows that, if... Figure 1 As shown, the traditional oil chamber top cover 1' is made of cast aluminum material, which has insufficient structural strength. Under extreme arc faults (5MJ level), there is a risk of the top cover tearing, threatening equipment safety. Summary of the Invention

[0004] In view of this, the present invention proposes an explosion-proof top cover, oil chamber structure and top cover structure strength verification method for on-load tap changers, aiming to solve the problem that the existing converter transformer oil chamber top cover structure has insufficient strength and poses a risk of top cover tearing that threatens equipment safety.

[0005] On one hand, the present invention proposes an explosion-proof top cover for an on-load tap changer, the explosion-proof top cover comprising: a top cover body; wherein, the top cover body is provided with a ring of small bolt holes arranged in a circle, and the outer edge of the top cover body is provided with a plurality of spaced connecting plates extending outward along its circumference, each of the connecting plates being provided with large bolt holes, the large bolt holes and the small bolt holes being used to install bolt assemblies to realize the connection between the explosion-proof top cover and the top connecting flange of the oil drum; the connection between the top cover body and each of the connecting plates is provided with a plurality of radial reinforcing ribs, each of the radial reinforcing ribs extending outward from the center position of the top cover body and extending to the large bolt holes on the connecting plates;

[0006] The total number of radial stiffeners is determined based on the number of large bolt holes; the total number of radial stiffeners is determined using the following formula:

[0007] N1≥0.5N2+1;

[0008] Where N1 is the total number of radial stiffeners and N2 is the number of large bolt holes.

[0009] Furthermore, the number of large bolt holes in the explosion-proof top cover for the on-load tap changer is determined based on the number of small bolt holes.

[0010] Furthermore, for the explosion-proof top cover of the above-mentioned on-load tap changer, the number of large bolt holes is determined using the following formula:

[0011] N2 = ceiling(N3 / 3) + i;

[0012] Where N3 is the number of small bolt holes, N2 is the number of large bolt holes, and i is the bolt adjustment amount.

[0013] Furthermore, for the explosion-proof top cover of the above-mentioned on-load tap changer, the bolt adjustment amount is determined based on the number of small bolt holes.

[0014] Furthermore, regarding the explosion-proof top cover for the aforementioned on-load tap changer, when determining the bolt adjustment amount based on the number of small bolt holes:

[0015] First, obtain the number N3 of the small bolt holes;

[0016] Set a preset bolt hole reference value matrix M, and set M(M1, M2, M3), where M1 is the first preset bolt hole reference value, M2 is the second preset bolt hole reference value, and M3 is the third preset bolt hole reference value; where M1 < M2 < M3.

[0017] The bolt adjustment amount is determined based on the relationship between the number of small bolt holes and the reference values ​​of each preset bolt hole.

[0018] Furthermore, in the aforementioned explosion-proof top cover for on-load tap changers, the determination of the bolt adjustment amount based on the relationship between the number of small bolt holes and the reference values ​​of each preset bolt hole specifically involves:

[0019] When ΔM < M1, the first preset adjustment amount i1 is selected as the bolt adjustment amount;

[0020] When M1≤ΔM<M2, the second preset adjustment amount i2 is selected as the bolt adjustment amount;

[0021] When M2≤ΔM<M3, the third preset adjustment amount i3 is selected as the bolt adjustment amount;

[0022] When ΔM≥M3, the fourth preset adjustment amount i4 is selected as the bolt adjustment amount. Wherein, i1>i2>i3>i4.

[0023] Furthermore, in the aforementioned explosion-proof top cover for on-load tap changers, the width and height of the radial reinforcing ribs satisfy the following relationship:

[0024] 3 ≥ H / W ≥ 1;

[0025] W ≥ 5 mm;

[0026] Where, H is the height of the radial reinforcing rib, and W is the width of the radial reinforcing rib.

[0027] On the other hand, the present invention also proposes an on-load tap-changer oil chamber structure provided with the explosion-proof top cover for the on-load tap-changer described above.

[0028] Further, for the on-load tap-changer oil chamber structure described above, the oil chamber structure includes: an oil cylinder, which is connected to the top cover through a top transfer flange at the top; a bottom cover, which is arranged and connected to the bottom end of the oil cylinder.

[0029] Further, for the on-load tap-changer oil chamber structure described above, the oil cylinder is connected to the top transfer flange through top connection bolts, and the oil cylinder is connected to the bottom cover through bottom connection bolts; the number of the bottom connection bolts is less than the number of the top connection bolts, and the difference between the two is greater than or equal to a preset difference.

[0030] Further, for the on-load tap-changer oil chamber structure described above, determine the preset difference based on the voltage level of the transformer installed in the oil chamber structure.

[0031] Further, for the on-load tap-changer oil chamber structure described above, when determining the preset difference based on the voltage level of the transformer installed in the oil chamber structure:

[0032] First, obtain the voltage level ΔV of the transformer installed in the oil chamber structure;

[0033] Set a preset voltage level reference value matrix V, set V(V1, V2, V3), where V1 is the first preset voltage level reference value, V2 is the second preset voltage level reference value, and V3 is the third preset voltage level reference value;

[0034] Determine the preset difference according to the relationship between the voltage level of the transformer and each preset voltage level reference value.

[0035] Further, for the on-load tap-changer oil chamber structure described above, the determination of the preset difference according to the relationship between the voltage level of the transformer and each preset voltage level reference value is specifically:

[0036] When ΔV < V1, select the first bolt adjustment difference k1 as the preset difference;

[0037] When V2 ≤ ΔV < V3, select the second bolt adjustment difference k2 as the preset difference;

[0038] When ΔV ≥ V3, select the third bolt adjustment difference k3 as the preset difference;

[0039] Among them, 2 <k1<k2≤2k1-1<k3<3k1-1。

[0040] The explosion-proof top cover and oil chamber structure for on-load tap changers provided by this invention achieve radial expansion by extending a connecting plate outward from the outer edge of the top cover body. A double-layer bolted connection structure is formed through small bolt holes on the top cover body and large bolt holes on the connecting plate. The outer layer of bolts can secure the top cover to the transition flange or oil tank top cover, achieving a double-layer bolted connection between the top cover and the transition flange or oil tank top cover. In existing technologies, only a single bolt ring on the original circular top cover is used for fastening to the oil chamber. Under fault pressure impact, the center of the top cover bulges and deforms. The deformation of the bolt holes is suppressed due to the tightening of the bolts, resulting in shear force at the bolt holes, leading to a low failure threshold and a high-risk failure structure. In this embodiment, the double-layer bolted connection structure disperses the load at a single bolt hole, reduces its strain value, strengthens the connection strength between the top cover and the transition flange or oil tank top cover, avoids connection failure, and also prevents deformation failure of the top cover. Radial reinforcing ribs on the top cover extend from the center of the top cover to the radially expanded structure. At the large bolt holes, the upward convex deformation tendency of the top cover in the middle under the impact pressure of the fault can be suppressed, realizing the overall structural reinforcement of the top cover, suppressing the local deformation at the two bolt holes, avoiding the transformation of the material stress state at the bolt holes into a shear state, reducing the failure threshold, and making the failure priority of the top cover lower, so that the insulating oil in the on-load tap changer oil chamber structure can be preferentially discharged into the transformer oil tank, further protecting the top cover, and avoiding direct contact between the insulating oil and air, which can effectively avoid deflagration accidents. In particular, it improves the explosion-proof performance of the tap changer and avoids deflagration accidents. Without changing the oil chamber structure and materials, or the connection structure between the tap changer and the transformer oil tank, it achieves a higher energy level of arc fault defense, effectively avoiding deflagration accidents. At the same time, it allows the top cover to open a large-diameter vent, which can improve the venting capacity, effectively suppress the overpressure peak and overpressure duration during the fault, and solves the problem that the existing converter transformer oil chamber top cover structure is not strong enough and there is a risk of top cover tearing that threatens equipment safety.

[0041] Furthermore, this invention also proposes a top cover verification method for structural verification of the aforementioned explosion-proof top cover for on-load tap changers. This method includes the following steps: based on the hole connection characteristics and radial reinforcing rib position features of the top cover structure, the top cover is divided into regions to obtain multiple structural units; based on the division results of each structural unit, a failure risk calculation mechanism is constructed, and each structural unit is calculated sequentially to obtain the failure strain threshold of each structural unit; based on the failure strain threshold of each structural unit, the cumulative failure strain threshold of each structural unit is statistically calculated, and combined with the equivalent plastic strain of the metal material used in the top cover, the failure risk coefficient of each structural unit is obtained; the failure risk coefficient of each structural unit is compared with the failure threshold, and when the failure risk coefficient of any structural unit is greater than or equal to the failure threshold, the top cover structure is determined to have failed.

[0042] Furthermore, in the above-mentioned top cover verification method, the step of constructing a failure risk calculation mechanism based on the division results of each structural unit of the top cover and calculating each structural unit in sequence is as follows: based on the metal material used in the top cover, different failure model coefficients for the corresponding materials are set to form a failure risk calculation mechanism, and based on the failure risk calculation mechanism, corresponding calculation measures are used to calculate each structural unit in sequence.

[0043] Furthermore, in the above-mentioned top cover verification method, the failure strain threshold of each structural unit of the top cover is calculated using the following formula:

[0044] ;

[0045] The top cover is made of metal. Let be the failure strain threshold of the i-th structural unit of the top cover; i = 1, 2, 3, ..., N; N is the number of structural units of the top cover; Let be the relative strain rate of the i-th structural element of the top cover, D1~D5 be the failure model parameters of the top cover metal material, and m be the temperature coefficient of the top cover structural element. Let i be the stress triaxiality of the i-th structural unit of the top cover. The relative temperature of the top cover structural unit.

[0046] Furthermore, in the above-mentioned roof verification method, the stress triaxiality of the i-th structural unit of the roof is calculated using the following formula:

[0047] ;

[0048] in, Let be the hydrostatic pressure of the i-th structural unit of the top cover; Let be the equivalent stress of the i-th structural unit of the top cover.

[0049] Furthermore, in the above-mentioned top cover verification method, the relative temperature of the top cover structural unit is calculated using the following formula:

[0050] ;

[0051] in, The relative temperature of the top cover structural unit; T room At room temperature; T melt T represents the melting point temperature of the metal material used for the top cover; T represents the current temperature.

[0052] Furthermore, in the above-mentioned roof verification method, the failure risk coefficient of each structural unit of the roof is calculated using the following formula:

[0053] ;

[0054] in, Let be the failure risk coefficient of the i-th structural unit of the top cover; Let be the equivalent plastic strain of the i-th structural unit of the top cover; Let t be the failure strain threshold of the i-th structural unit of the top cover; i = 1, 2, 3, ..., N; N is the total number of structural units of the top cover; t is time; t0 is the initial moment of the impact load; TT is the total duration of the impact load.

[0055] The top cover verification method provided by this invention determines whether the top cover structure has failed by performing a combined verification of the top cover, verifies the structural performance of the top cover, ensures the safety of the top cover, improves the explosion-proof performance of the tap changer, and avoids combustion and explosion accidents. It achieves higher energy level arc fault defense without changing the oil chamber structure and materials or the connection structure between the tap changer and the transformer oil tank, effectively avoiding combustion and explosion accidents. Attached Figure Description

[0056] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0057] Figure 1 This is a schematic diagram of the oil chamber of an on-load tap changer provided in the prior art.

[0058] Figure 2 This is a schematic diagram of the structure of the explosion-proof top cover provided in an embodiment of the present invention;

[0059] Figure 3 This is a partial schematic diagram of the explosion-proof top cover connection structure provided in an embodiment of the present invention;

[0060] Figure 4 Deformation cloud diagram of the explosion-proof top cover under impact load provided in the embodiment of the present invention;

[0061] Figure 5 Deformation contour map of a top cover without radial stiffeners under the same impact load, provided for an embodiment of the invention;

[0062] Figure 6 A cross-sectional view of the on-load tap changer oil chamber provided in an embodiment of the present invention;

[0063] Figure 7 A flowchart illustrating the method for verifying the strength of the roof structure provided in an embodiment of the present invention;

[0064] Explanation of reference numerals in the attached figures:

[0065] 1'-Traditional oil chamber top cover, 1-Top cover body, 11-Small bolt hole, 12-Transition arc, 13-Relief port, 14-Drive shaft mounting hole, 15-Gear position observation hole, 2-Connecting plate, 21-Large bolt hole, 3-Radial reinforcing rib, 4-Oil cylinder, 5-Top connecting flange, 6-Inner ring bolt, 7-Outer ring large bolt, 8-Pressure release mechanism. Detailed Implementation

[0066] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0067] Top cover example:

[0068] See Figure 2 This is a schematic diagram of the structure of an explosion-proof top cover for an on-load tap changer provided in an embodiment of the present invention. As shown in the figure, the explosion-proof top cover for an on-load tap changer includes: a top cover body 1, a connecting plate 2, and radial reinforcing ribs 3.

[0069] The top cover body 1 is provided with a ring of small bolt holes 11 arranged in a circle. Furthermore, the outer edge of the top cover body 1 is provided with several spaced connecting plates 2 along its circumference. Each connecting plate 2 is provided with a large bolt hole 21. The large bolt hole 21 and the small bolt hole 11 are used to install bolt assembly 3 to connect the explosion-proof top cover and the top connecting flange 5 of the oil cylinder 4.

[0070] Specifically, the top cover body 1 can be a disc-shaped structure. Several small bolt holes 11 are provided along its outer edge. These small bolt holes 11 are arranged circumferentially along the circumference of the top cover body, and in particular, the circumference of the small bolt holes 11 can be coaxially arranged with the top cover body 11 to ensure the connection stability of the top cover body 1. The small bolt holes 11 are fastened by inner ring bolts 6. To accommodate the connection of a load tap changer, connecting plates 2 are provided on the outer edge of the top cover body 1, extending radially outward from the center. Multiple connecting plates 2 are spaced apart at different positions on the outer edge of the top cover body 1. In this embodiment, four connecting plates 2 are used as an example. The arrangement of the four connecting plates 2 can be determined and adjusted according to actual conditions. Of course, the number of connecting plates 2 can also be other, depending on actual conditions. This embodiment does not impose any limitations on this. Furthermore, each connecting plate 2 can be a fan-shaped structure, and the radial width of the connecting plate 2 can also be determined according to actual conditions. In this embodiment, a transition arc 12 can be provided at the connection between the outer edge of the top cover body 1 and the connecting plate 2 to avoid stress concentration. In this embodiment, each connecting plate 2 is also provided with multiple large bolt holes 21. These large bolt holes 21 can be arranged circumferentially, and the large bolt holes 21 on each connecting plate 2 can be equally spaced from the outer edge of the corresponding connecting plate 2. That is, the distance between each large bolt hole 21 and the outer edge of the corresponding connecting plate 2 is equal and smaller than the radius of the large bolt hole 21, ensuring a solid portion between the large bolt hole and the outer edge of the connecting plate 2, thus ensuring the stability of the connecting plate 2. The distance between each large bolt hole 21 and the outer edge of the corresponding connecting plate 2 can be determined according to actual conditions. In this embodiment, each connecting plate 2 is provided with at least two large bolt holes 21, which are fastened by outer ring large bolts 7.

[0071] Several radial reinforcing ribs 3 are provided at the connection between the top cover body 1 and each connecting plate 2. Each radial reinforcing rib 3 extends outward from the center of the top cover body 1 and extends to the large bolt hole 21 on the connecting plate 2.

[0072] Specifically, the explosion-proof top cover has several radial reinforcing ribs 3 at the connection points between the top cover body 1 and each connecting plate 2. There can be at least two radial reinforcing ribs 3, with at least one arranged radially along the top cover body 1. The other radial reinforcing ribs 3 on the connecting plate 2 are arranged at an angle to the radially arranged radial reinforcing ribs 3, and the spacing between the radial reinforcing ribs 3 gradually increases from the center of the top cover body 1 outwards. Each radial reinforcing rib 3 extends outwards from the center of the radial reinforcing rib 3 on the top cover body 1 to the large bolt hole 21 on the connecting plate 2. Furthermore, each radial reinforcing rib 3 on the connecting plate 2 has a solid portion between it and the large bolt hole 21 to prevent the radial reinforcing rib 3 from interfering with the use of the large bolt hole 21. The arrangement of the radial reinforcing ribs 3 can suppress the tendency of the top cover to bulge upwards under fault impact pressure.

[0073] In this embodiment, the number of large bolt holes 21 affects the connection strength of the top cover structure and the failure performance of the top cover connection. To improve the structural stability of the top cover, especially the connection stability, the number of large bolt holes 21 can be determined based on the number of small bolt holes 11. Specifically, the number of small bolt holes 11 can be determined according to the actual situation; and the number of large bolt holes 21 can be determined based on the number of small bolt holes 11. The number of large bolt holes can be determined using the following formula:

[0074] N2 = ceiling(N3 / 3) + i;

[0075] Where N3 is the number of small bolt holes, N2 is the number of large bolt holes (i.e., the total number), and i is the bolt adjustment amount.

[0076] In this embodiment, the bolt adjustment amount can be determined based on the number of small bolt holes. When determining the bolt adjustment amount based on the number of small bolt holes:

[0077] First, obtain the number of small bolt holes, N3;

[0078] Set a preset bolt hole reference value matrix M, and set M(M1, M2, M3), where M1 is the first preset bolt hole reference value, M2 is the second preset bolt hole reference value, and M3 is the third preset bolt hole reference value; where M1 < M2 < M3.

[0079] The bolt adjustment amount is determined based on the relationship between the number of small bolt holes and the reference values ​​of each preset bolt hole.

[0080] It can be seen that by selecting the bolt adjustment amount based on the relationship between the number of small bolt holes and the reference values ​​of each preset bolt hole, the number of large bolt holes can be further adapted and adjusted according to the number of small bolt holes, thereby selecting a suitable number of large bolt holes to improve the structural strength and connection strength of the top cover.

[0081] The bolt adjustment amount is determined based on the relationship between the number of small bolt holes and the reference values ​​of each preset bolt hole, specifically as follows:

[0082] When ΔM < M1, the first preset adjustment amount i1 is selected as the bolt adjustment amount;

[0083] When M1≤ΔM<M2, the second preset adjustment amount i2 is selected as the bolt adjustment amount;

[0084] When M2≤ΔM<M3, the third preset adjustment amount i3 is selected as the bolt adjustment amount;

[0085] When ΔM ≥ M3, the fourth preset adjustment amount i4 is selected as the bolt adjustment amount. Where i1 > i2 > i3 > i4. For example, i1, i2, i3, and i4 can be 8, 6, 4, and 2 respectively. For instance, when ΔM < 10, the bolt adjustment amount is 8; when 10 ≤ ΔM < 15, 6 is selected as the bolt adjustment amount; when 15 ≤ ΔM < 20, 4 is selected as the bolt adjustment amount; and when ΔM ≥ 20, 2 is selected as the bolt adjustment amount.

[0086] It can be seen that when there are more small bolt holes, reducing the bolt adjustment amount can ensure that when there are fewer small bolt holes, the number can be relatively increased by using a larger bolt adjustment amount, thus avoiding the problem of insufficient connection strength caused by excessively small large bolt holes.

[0087] In other words, when determining the number of large bolt holes:

[0088] First, determine the bolt adjustment amount based on the number of small bolt holes; then, based on the bolt adjustment amount and the number of small bolt holes, determine the number of large bolt holes according to the following formula.

[0089] N2 = ceiling(N3 / 3) + i.

[0090] In this embodiment, the large bolt holes 21 can be evenly distributed on multiple connecting plates 2, for example, they can be arranged at equal intervals on the connecting plates 2, or they can be adjusted according to the curvature of the corresponding connecting plates 2.

[0091] In this embodiment, the arrangement, especially the number, of the radial reinforcing ribs 3 directly affects the strength of the top cover, particularly the structural strength at the location of the vent. To prevent tearing in the middle of the top cover, the total number of radial reinforcing ribs 3 can be determined based on the number of large bolt holes 21. Specifically, the total number of radial reinforcing ribs is determined using the following formula:

[0092] N1≥0.5N2+1;

[0093] Where N1 is the total number of radial stiffeners and N2 is the number of large bolt holes.

[0094] In this embodiment, the width and height of the radial stiffener satisfy the following relationship:

[0095] 3≥H / W≥1;

[0096] W≥5mm;

[0097] Where H is the height of the radial stiffener and W is the width of the radial stiffener.

[0098] In this embodiment, the top cover body 1 may also be provided with a vent 13, a drive shaft mounting hole 14, and a gear position observation hole 15. The vent 13 can be arranged at an angle, avoiding other components of the top cover through an inclined flange, to achieve overpressure relief. The vent 13 can be equipped with a pressure relief mechanism 8. Compared with the existing technology where the pressure relief device and its flow diameter are too small, limiting the relief capacity and making it impossible to quickly relieve overpressure in case of fault, in this embodiment, the vent 13 adopts a large diameter, especially a vent 170mm or larger, to achieve more efficient overpressure relief. The pressure relief mechanism 8, such as a pressure relief valve or an explosion-proof membrane, can be installed through the flange. At the same time, the radial reinforcing ribs 3 can suppress the weakening of the top cover's rigidity due to the large opening.

[0099] Traditional tap changers use 8.8 grade high-strength bolts with a yield strength of 640 MPa and a tensile strength as high as 800 MPa, while the yield strength of aluminum top cover material is only 240 MPa and the tensile strength is 300 MPa, both far lower than that of high-strength bolts. Therefore, during an arc fault, the top cover deforms preferentially, and strain concentrates on the top cover. To coordinate deformation and fully utilize the mechanical properties of the top cover, bolts, and other structures, materials with similar mechanical properties must be selected. Therefore, the top cover material is changed from die-cast aluminum to steel. In this embodiment, the explosion-proof top cover can be a steel top cover, replacing the currently used cast aluminum material. The steel top cover can use steels such as Q235, Q255, and SUS304, which have better yield strength, ultimate tensile strength, and ductility, and their purchase and processing costs are lower. It can also be cast. The shear resistance of the threaded holes or threads of the top cover is improved, thereby improving the explosion-proof capability. Meanwhile, in this embodiment, the bolt holes on the top cover are straight holes, which are fastened by bolt-nut connection. Compared with the prior art, which changes the top cover thread from the top cover to a bolt-nut connection, the use of bolts and nuts of the same strength grade for fastening can improve the explosion-proof performance.

[0100] In this embodiment, the explosion-proof top cover can be a steel top cover, replacing the existing cast aluminum material. The steel top cover can be made of steel with better yield strength, ultimate tensile strength and ductility, such as Q235, Q255, SUS304, and its purchase and processing costs are lower, and it can also be cast.

[0101] like Figure 3 and Figure 4 As shown, the arrangement of radial stiffeners can greatly reduce the total displacement in the strain analysis of the top cover. Therefore, the top cover has stronger impact resistance and deformation stiffness.

[0102] In summary, the explosion-proof top cover for on-load tap changers provided in this embodiment achieves radial expansion by extending a connecting plate outward from the outer edge of the top cover body. A double-layer bolted connection structure is formed through small bolt holes on the top cover body and large bolt holes on the connecting plate. The outer layer of bolts secures the top cover to the transition flange or oil tank top cover, achieving a double-layer bolted connection between the top cover and the transition flange or oil tank top cover. In existing technologies, only a single bolt ring on the original circular top cover is used for fastening to the oil chamber. Under fault pressure impact, the center of the top cover bulges and deforms. The deformation of the bolt holes is suppressed due to the tightening of the bolts, resulting in shear force at the bolt holes, leading to a low failure threshold and a high-risk failure structure. In this embodiment, the double-layer bolted connection structure disperses the load at a single bolt hole, reducing its strain value and strengthening the connection strength between the top cover and the transition flange or oil tank top cover, preventing connection failure and also preventing deformation failure of the top cover. The radial reinforcing ribs on the top cover extend from the center of the top cover to the large bolts on the radially expanded structure. At the bolt holes, the upward convex deformation tendency of the top cover in the middle under the impact pressure of the fault can be suppressed, realizing the overall structural reinforcement of the top cover, suppressing the local deformation at the two bolt holes, preventing the material stress state at the bolt holes from changing to the shear state, reducing the failure threshold, and making the failure priority of the top cover lower, so that the insulating oil in the on-load tap changer oil chamber structure can be preferentially discharged into the transformer oil tank, further protecting the top cover, and avoiding direct contact between the insulating oil and air, which can effectively prevent deflagration accidents. In particular, it improves the explosion-proof performance of the tap changer and avoids deflagration accidents. Without changing the oil chamber structure and materials, or the connection structure between the tap changer and the transformer oil tank, it achieves a higher energy level of arc fault defense, effectively preventing deflagration accidents. At the same time, it allows the top cover to open a large-diameter vent, which can improve the venting capacity, effectively suppress the overpressure peak and overpressure duration during the fault, and solves the problem that the existing converter transformer oil chamber top cover structure is not strong enough and there is a risk of top cover tearing that threatens equipment safety.

[0103] Oil chamber example:

[0104] See also Figure 3 and Figure 6 This embodiment also proposes an on-load tap changer oil chamber structure, which includes the aforementioned explosion-proof top cover, oil cylinder 4, and bottom cover (not shown in the figure). The top of the oil cylinder 4 (relative to...) Figure 6 The top cover (as shown in the diagram) is connected to the top cover via a top adapter flange 5; the bottom cover is installed and connected to the bottom end of the oil cylinder 4. The specific implementation process of the explosion-proof top cover for the on-load tap changer is described above and will not be repeated here.

[0105] Specifically, the oil cylinder 4 is connected to the top transition flange 5 via top connecting bolts 41, and the oil cylinder 4 is connected to the bottom cover via bottom connecting bolts 42. Both the top connecting bolts 41 and the bottom connecting bolts 42 are arranged circumferentially around the oil cylinder 4 and at intervals. The oil cylinder 4 can be connected to the bottom cover via a bottom transition flange, and the oil cylinder 4 can be connected to the bottom transition flange via bottom connecting bolts 42. Figure 6 The Z-axis is the axial direction of oil cylinder 4, and the X-axis is the left-right direction on the horizontal plane perpendicular to the axial direction of oil cylinder 4.

[0106] In this embodiment, the oil chamber is divided into different regions according to the possible location of the fault. For example: Region 1: main contacts and their upper part; Region 2: isolation contacts and vacuum tube area; Region 3: transition resistor and its lower part. Combined with the fault energy, the corresponding relationship between pressure relief by closing the top cover and pressure relief by rupture at the bottom of the oil chamber is determined according to the classification of less than 2MJ, 2-5MJ, and 5MJ.

[0107] Arc faults in tap changers can occur in: Zone 1 – main contacts and their upper part; Zone 2 – isolating contacts and vacuum tube area; Zone 3 – transition resistor and its lower part. The explosion-proof response of the tap changer varies depending on the energy level of the fault occurring in different locations. When the arc point is higher (Zone 1), the top cover is impacted first and under greater pressure than the bottom cover. Therefore, when the arc energy is high (e.g., 5 MJ), the connection between the tap changer oil chamber and the bottom transition flange should be broken first, allowing the oil inside the tap changer to connect with the transformer tank, thereby reducing overpressure and preventing the top cover from being blown off. When the arc point is lower (Zone 3), the bottom cover is impacted first. When the arc energy is high (e.g., 5 MJ), the connection between the bottom cover and the oil chamber is broken first, allowing the oil inside the tap changer to connect with the transformer, thus suppressing overpressure. When a discharge occurs in the middle of the tap changer, because the density of the air bubbles is lighter than that of the insulating oil, the impact pressure acts more on the top cover. Therefore, when the arc energy is high, it can damage the connection structure between the oil tank and the transfer flange, as well as the connection structure between the bottom cover and the oil chamber, thereby connecting the insulating oil in the tap changer to the transformer to reduce overvoltage. When the arc energy is low, such as 2MJ, the tap changer can be explosion-proof by relying on the deformation of the tap changer oil chamber, the destruction of the internal electrical structure, and the pressure relief valve.

[0108] Therefore, considering that the connection structure between the oil cylinder and the top transition flange is close to the top cover, the strength of this connection structure should be slightly higher than that between the bottom cover and the oil cylinder. This makes the bottom cover more susceptible to damage in a fault, forcing the tap changer insulating oil to enter the transformer tank from the bottom cover, thus reducing the risk of combustion and explosion. Therefore, the connection strength between the top cover and the top transition flange should be greater than the connection strength between the oil cylinder and the top transition flange, and greater than the connection strength between the bottom cover and the oil cylinder.

[0109] Therefore, the top cover and the top transfer flange are connected by double-layer bolts, and the connection strength is greater than that between the oil cylinder and the top transfer flange. To ensure that the connection strength between the oil cylinder and the top transfer flange is greater than that between the bottom cover and the oil cylinder, preferably, the number of bottom connection bolts 42 is less than that of the top connection bolts 41, and the difference between the two is greater than or equal to a preset difference. To further ensure that the bottom cover is preferentially damaged in case of failure, the preset difference can be determined based on the voltage level of the transformer installed in the oil chamber structure.

[0110] In this embodiment, when determining the preset difference based on the voltage level of the transformer installed in the oil chamber structure:

[0111] First, obtain the voltage level ΔV of the transformer installed in the oil chamber structure;

[0112] Set a preset voltage level reference value matrix V, set V(V1, V2, V3), where V1 is the first preset voltage level reference value, V2 is the second preset voltage level reference value, and V3 is the third preset voltage level reference value; where V1 < V2 < V3;

[0113] Determine the preset difference according to the relationship between the voltage level of the transformer and each preset voltage level reference value.

[0114] It can be seen that by the relationship between the voltage level of the transformer installed in the oil chamber structure and each preset voltage level reference value, the difference in the number of the bottom connection bolts 42 and the top connection bolts 41 is selected, and the difference in the number of the bottom connection bolts 42 and the top connection bolts 41 can be effectively adjusted according to the voltage level of the transformer, so that the bolts with appropriate numbers can be selected to be installed on the oil cylinder to realize the connection fastening at the top and the bottom, so as to ensure the connection strength under different voltage levels and at the same time, the connection of the bottom cover can be preferentially damaged.

[0115] In this embodiment, when determining the preset difference according to the relationship between the voltage level of the transformer and each preset voltage level reference value, specifically:

[0116] When ΔV < V1, select the first bolt adjustment difference k1 as the preset difference;

[0117] When V2 ≤ ΔV < V3, select the second bolt adjustment difference k2 as the preset difference;

[0118] When ΔV ≥ V3, select the third bolt adjustment difference k3 as the preset difference;

[0119] Among them, 2 < k1 < k2 ≤ 2k1 - 1 < k3 < 3k1 - 1.

[0120] It can be seen that as the voltage level of the transformer increases, the difference in the number of bottom connecting bolts 42 and top connecting bolts 41 is increased. That is, a connection method with a large difference in the number of top and bottom connecting bolts of the oil tank is provided on transformers with high voltage levels. This ensures that the bottom cover of the transformer with high voltage levels can be destroyed first, avoiding damage to the top cover that would lead to leakage of hydraulic oil. In particular, it realizes the reasonable configuration of failure priority of the tap changer, so that the oil chamber-bottom cover connection structure breaks first, followed by the oil chamber-transfer flange connection structure, and finally the top cover-transfer flange connection structure, thus avoiding leakage of insulating oil.

[0121] Because the hydraulic control valve assembly has the above-mentioned effects, the scissor lift aerial work platform equipped with this control valve assembly also has the corresponding technical effects.

[0122] Verification method example:

[0123] See Figure 7 The figure shows a flowchart of the top cover structure strength verification method provided in this embodiment of the invention. As shown, this top cover verification method can perform the structural verification of the explosion-proof top cover for on-load tap changers, and may include the following steps:

[0124] Risk classification step S1 involves dividing the top cover into fishing areas based on the hole connection characteristics of the top cover structure, resulting in multiple structural units.

[0125] Specifically, based on the hole connection characteristics and radial stiffener position features of the top cover structure, such as hole attributes (e.g., whether the hole is a bolt connection hole or a functional hole like a vent hole), the top cover is divided into structural units, resulting in multiple structural units, which can be categorized as high-risk, medium-risk, and low-risk zones. For example, the periphery of bolt connection holes and radial stiffener positions can be classified as a low-risk zone, while the periphery of functional holes can be classified as a high-risk zone. The specific definition of the surrounding areas can be determined according to actual conditions; for example, positions at a distance less than or equal to j*d from the bolt connection hole are considered low-risk zones, where d can be the diameter of the bolt connection hole, and j is the low-risk coefficient, which can be determined based on actual conditions such as the top cover thickness. The overlapping areas of high-risk and low-risk zones are medium-risk zones, and areas on the top cover other than high-risk and low-risk zones are also medium-risk zones.

[0126] In step S2, the failure threshold calculation is performed by constructing a failure risk calculation mechanism based on the division results of each structural unit of the top cover, and calculating the failure strain threshold of each structural unit of the top cover in sequence.

[0127] Specifically, based on the classification of low-risk, medium-risk, and high-risk zones, different failure model coefficients are set for corresponding materials to form a failure risk calculation mechanism. Based on this mechanism, corresponding calculation measures are applied sequentially to each risk zone. The failure strain threshold for each structural unit of the roof is calculated using the following formula:

[0128] ;

[0129] The top cover is made of metal. Let be the failure strain threshold of the i-th structural unit of the top cover; i = 1, 2, 3, ..., N; N is the number of structural units of the top cover; Let be the relative strain rate of the i-th structural element of the top cover, D1~D5 be the failure model parameters of the top cover metal material, and m be the temperature coefficient of the top cover structural element. Let i be the stress triaxiality of the i-th structural unit of the top cover. The relative temperature of the top cover structural unit.

[0130] In this embodiment, the values ​​of D1 to D5 can be determined based on the metal material. Different metal materials have different values. In particular, the values ​​of D1 to D5 can be determined based on the "Handbook of Commonly Used Material Parameters for Finite Element Analysis" and "2025 - Dynamic Constitutive Model and Deformation Mechanism of UHV Transformer Tank Material under High Loading Rate".

[0131] In this embodiment, the stress triaxiality of the i-th structural unit of the top cover is calculated using the following formula:

[0132] ;

[0133] in, Let be the hydrostatic pressure of the i-th structural unit of the top cover; Let be the equivalent stress of the i-th structural unit of the top cover.

[0134] In this embodiment, the relative temperature of the top cover structural unit is calculated using the following formula:

[0135] ;

[0136] in, The relative temperature of the top cover structural unit; T room At room temperature; T melt T represents the melting point temperature of the metal material used for the top cover; T represents the current temperature.

[0137] In step S3, the failure risk coefficient of each structural unit of the top cover is compared with the failure threshold. When the failure risk coefficient of any structural unit of the top cover is greater than or equal to the failure threshold, it is determined that the top cover structure has failed.

[0138] Specifically, the failure risk coefficient of each structural unit of the roof is calculated using the following formula:

[0139] ;

[0140] in, Let be the failure risk coefficient of the i-th structural unit of the top cover; Let be the equivalent plastic strain of the i-th structural unit of the top cover; Let t be the failure strain threshold of the i-th structural unit of the top cover; i = 1, 2, 3, ..., N; N is the total number of structural units of the top cover; t is time; t0 is the initial moment of the impact load; TT is the total duration of the impact load.

[0141] In failure judgment step S4, the failure risk coefficient of each structural unit of the top cover is compared with the failure threshold. When the failure risk coefficient of any structural unit of the top cover is greater than or equal to the failure threshold, the top cover structure is determined to have failed.

[0142] Specifically, the failure threshold can be 1. The failure risk coefficient of each structural unit of the top cover can be compared with the failure threshold. When the failure risk coefficient of any structural unit is greater than or equal to the failure threshold, the top cover structure fails, and the top cover is then optimized, especially for structural units with high failure risk coefficients.

[0143] In summary, by verifying the top cover in conjunction with other components, it is possible to determine whether the top cover structure has failed, thus verifying the structural performance of the top cover, ensuring its safety, improving the explosion-proof performance of the tap changer, and preventing combustion and explosion accidents. This approach enables higher-energy-level arc fault defense without altering the oil chamber structure and materials or the connection structure between the tap changer and the transformer tank, effectively preventing combustion and explosion accidents.

[0144] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0145] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0146] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An explosion-proof top cover for a load tap changer, characterized by Comprise: A top cover body; wherein, A circle of small bolt holes is arranged on the top cover body in a circumferential direction, and a plurality of connection plates are arranged on the outer edge of the top cover body in the circumferential direction, each of the connection plates is provided with a large bolt hole, and the small bolt hole and the large bolt hole are used to install a bolt assembly to realize the connection between the explosion-proof top cover and the flange at the top of the oil cylinder; A plurality of radial reinforcing ribs are arranged at the connection between the top cover body and each of the connection plates, each of the radial reinforcing ribs extends outward from the center of the top cover body and extends to the large bolt hole on the connection plate; The total number of radial reinforcing ribs is determined based on the number of large bolt holes; The total number of radial reinforcing ribs is determined by the following formula: N1≥0.5N2+1; Wherein, N1 is the total number of radial reinforcing ribs, and N2 is the number of large bolt holes; The number of large bolt holes is determined based on the number of small bolt holes; The number of large bolt holes is determined by the following formula: N2=ceiling(N3 / 3)+i; Wherein, N3 is the number of small bolt holes, N2 is the number of large bolt holes, and i is the bolt adjustment amount; The bolt adjustment amount is determined based on the number of small bolt holes; When determining the bolt adjustment amount based on the number of small bolt holes: First, the number N3 of small bolt holes is obtained; A preset bolt hole reference value matrix M is set, and M=[M1, M2, M3], wherein M1 is the first preset bolt hole reference value, M2 is the second preset bolt hole reference value, and M3 is the third preset bolt hole reference value; wherein M1 The bolt adjustment amount is determined according to the relationship between the number of small bolt holes and each of the preset bolt hole reference values; The bolt adjustment amount is determined according to the relationship between the number of small bolt holes and each of the preset bolt hole reference values, which is: When ΔM When M1≤ΔM When M2≤ΔM When ΔM≥M3, the fourth preset adjustment amount i4 is selected as the bolt adjustment amount; wherein i1>i2>i3>i4.

2. The explosion-proof top cover for a load tap changer according to claim 1, characterized in that The radial reinforcing rib width and height satisfy the following: 3≥H / W≥1; W≥5mm; Wherein, H is the height of the radial reinforcing rib, and W is the width of the radial reinforcing rib.

3. A structure of an oil chamber of an on-load tap changer, characterized by An explosion-proof top cover for a load tap changer is provided.

4. The oil chamber structure of the on-load tap changer according to claim 3, characterized by Further comprise: An oil cylinder, the top of which is connected to the top cover through a top adapter flange; A bottom cover, which is arranged and connected at the bottom end of the oil cylinder.

5. The load tap changer oil chamber structure of claim 4, wherein: The oil cylinder and the top adapter flange are connected through top connection bolts, and the oil cylinder and the bottom cover are connected through bottom connection bolts; The number of bottom connection bolts is less than the number of top connection bolts, and the difference between them is greater than or equal to a preset difference.

6. The OLTC oil chamber structure of claim 5, wherein a preset difference value is determined based on a voltage class of a transformer to which the oil chamber structure is installed.

7. The OLTC oil chamber structure of claim 6, wherein when the preset difference value is determined based on the voltage class of the transformer to which the oil chamber structure is installed: first, a voltage class AV of the transformer to which the oil chamber structure is installed is obtained; a preset voltage class reference value matrix V is set, V = [V1, V2, V3], wherein V1 is a first preset voltage class reference value, V2 is a second preset voltage class reference value, and V3 is a third preset voltage class reference value; and a preset difference value is determined according to a relationship between the voltage class of the transformer and each preset voltage class reference value.

8. The OLTC oil chamber structure of claim 7, wherein the preset difference value is determined according to the relationship between the voltage class of the transformer and each preset voltage class reference value, and specifically: when AV < V1, a first bolt adjustment difference value k1 is selected as the preset difference value; when V2≤ AV < V3, a second bolt adjustment difference value k2 is selected as the preset difference value; when AV≥ V3, a third bolt adjustment difference value k3 is selected as the preset difference value; and 2 < k1 < k2≤ 2k1-1< k3< 3k1-1. The structure checking method of the explosion-proof top cover for the OLTC according to claim 1 or 2 comprises the following steps: based on the hole connection characteristics and the radial stiffener position characteristics of the structure of the top cover, the top cover is regionally divided to obtain a plurality of structure units; according to the division results of each structure unit of the top cover, a failure risk calculation mechanism is constructed, each structure unit is calculated in turn, and a failure strain threshold of each structure unit of the top cover is obtained; 9. A method of roof checking, characterized in that based on the failure strain threshold of each structure unit of the top cover, a cumulative failure strain threshold of each structure unit of the top cover is counted, and in combination with the equivalent plastic strain of the metal material adopted by the top cover, a failure risk coefficient of each structure unit of the top cover is obtained; the failure risk coefficient of each structure unit of the top cover is compared with a failure threshold value, and when the failure risk coefficient of any structure unit of the top cover is greater than or equal to the failure threshold value, it is determined that the structure of the top cover fails.

10. The top cover checking method of claim 9, wherein according to the division results of each structure unit of the top cover, the failure risk calculation mechanism is constructed, and each structure unit is calculated in turn, and specifically: based on the metal material adopted by the top cover, different failure model coefficients corresponding to the material are set to form the failure risk calculation mechanism, and based on the failure risk calculation mechanism, each structure unit is calculated in turn by using the corresponding calculation measures. the failure strain threshold of each structure unit of the top cover is calculated by using the following formula: the stress triaxiality of the i-th structure unit of the top cover is calculated by using the following formula: the relative temperature of the structure unit of the top cover is calculated by using the following formula: the failure risk coefficient of each structure unit of the top cover is calculated by using the following formula:

11. The method of cap verification of claim 10, wherein, ​ ； The top cover is made of metal material; is the failure strain threshold of the i th structural unit of the top cover; i = 1, 2, 3, …, N; N is the number of the top cover structural units; is the corresponding strain rate of the i th structural unit of the top cover, D1~D5 are the failure model parameters of the top cover metal material, and m is the temperature coefficient of the top cover structural unit, is the stress triaxiality of the i th structural unit of the top cover, T * is the relative temperature of the top cover structural unit.

12. The method of cap verification of claim 11, wherein, ​ ； wherein hydrostatic pressure of the i-th structural unit of the top cover; equivalent stress of the i-th structural unit of the top cover.

13. The method of cap verification of claim 11, wherein, ​ ； Wherein, T * is the relative temperature of the top cover structure unit; T room is the room temperature; T melt is the melting point temperature of the metal material adopted by the top cover; T is the current temperature.

14. The method of cap verification of claim 11, wherein, ​ ； wherein, is the failure risk coefficient of the i-th structural unit of the roof; is the equivalent plastic strain of the i-th structural unit of the roof; is the failure strain threshold of the i-th structural unit of the roof; i = 1, 2, 3, …, N; N is the total number of structural units of the roof; t is time; t0is the initial time of the impact load; TTis the total action time of the impact load.

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