Transformer primary coil fixing method

Abstract

The application discloses a method for fixing a primary coil of a mutual inductor, and relates to the technical field of voltage mutual inductors; the method comprises the following steps: aligning a core clamp with the outer periphery of a core, wrapping the core clamp around the core, and then fixing the core clamp on one long side of the core; taking the long side of the other side of the core as a reference, uniformly winding a secondary coil on the outside of the long side according to the designed number of turns; winding a primary coil on the outside of the secondary coil; correspondingly welding a primary conductive sheet on the bottom outside of the primary coil, and synchronously adjusting the position during welding; aligning the upper end of a resin support with a cross-shaped slot countersunk bolt on a primary conductive sheet fixing seat; then aligning the lower end of the resin support with an oval countersunk hole of a support frame; slowly moving the primary coil along the long axis direction of the oval countersunk hole of the support frame, monitoring the distance between the primary coil and the core and the secondary coil through a measuring tool, and stopping until the designed insulation distance is reached; the method shortens the assembly time, has no air gap and interface cracking problem, and greatly improves the product qualification rate.

Description

Technical Field

[0001] This invention relates to the field of voltage transformer technology, and more specifically to a method for fixing the primary coil of a transformer. Background Technology

[0002] In the stable operation of a power system, voltage transformers, as key equipment for voltage measurement, protection, and control, directly affect the safe and efficient operation of the entire power network. The core components of this equipment mainly include the primary coil, secondary coil, and iron core. In the structural design of a fully insulated voltage transformer, the method of fixing the primary coil has a decisive impact on the overall performance, size control, and long-term operational reliability of the equipment, and is one of the core technical aspects of the design and manufacturing process of fully insulated voltage transformers.

[0003] Currently, the primary coil of traditional fully insulated voltage transformers is typically fixed using a metal support structure. This involves suspending the primary coil above a window or on the side wall of the toroidal core using metal screws, hanging plates, or frames, thus achieving a fixed assembly of the primary coil on the core. From a technical compatibility perspective, while this traditional fixing method meets the basic insulation performance requirements of fully insulated voltage transformers and ensures initial operation under normal conditions, in practical applications, especially with the increasing demands for miniaturization, high reliability, and low cost in power systems, this fixing method has gradually revealed several unavoidable technical drawbacks, as follows: Firstly, regarding equipment size control, since the metal hangers need to bear the entire weight of the primary coil, the cross-sectional area of ​​the metal hangers must be designed within a large range to ensure sufficient mechanical strength to avoid structural deformation or breakage. This design requirement directly leads to a significant increase in the overall size of the fully insulated voltage transformer, not only occupying more installation space but also making it difficult to adapt to the current development trend of compact switchgear. This creates a prominent contradiction with the industry's demand for miniaturization and integration of power equipment, limiting the expansion of the equipment's application scenarios in confined installation environments. Secondly, regarding insulation performance and operational stability, there is a significant difference in the coefficient of thermal expansion between metal materials and commonly used insulating materials such as epoxy resin in instrument transformers. When the equipment is under temperature-changing conditions (such as load fluctuations or alternating ambient temperatures), the volume changes caused by the different coefficients of thermal expansion of the two materials are inconsistent, resulting in significant shear stress at their joints. Long-term accumulated shear stress can not only lead to cracking of the insulation material but also cause displacement of the primary coil, disrupting the relative positional stability between the coil and the core, and the secondary winding. Simultaneously, the presence of metal hangers can easily create localized areas of concentrated electric field, significantly increasing the risk of partial discharge, which in severe cases may lead to insulation failure and threaten the long-term safe operation of the instrument transformer. Furthermore, regarding assembly efficiency and precision control, the installation process of traditional metal suspension structures involves multiple adjustment steps, such as the positioning and calibration of metal hangers and the precise control of coil suspension height. These steps are not only cumbersome and require a high level of technical skill from assembly personnel, but also make it difficult to accurately ensure that the insulation distance between the primary coil and the iron core, and between the secondary winding and the primary coil, meets the design standards. Deviations in insulation distance may further exacerbate the problem of uneven electric field distribution, while the long assembly time also makes it difficult to improve the production efficiency of the equipment, increasing the time cost in the production process. Finally, regarding production costs and product qualification rates, on the one hand, the procurement cost of metal materials is relatively high, and in order to prevent metal suspension components from rusting during operation, additional rust prevention treatments (such as galvanizing and painting) are required. At the same time, the processing of metal suspension components also requires multiple machining processes such as cutting, drilling, and grinding, all of which significantly increase the manufacturing cost of the equipment. On the other hand, during the epoxy resin casting process of the current transformer, the presence of the metal suspension structure can easily lead to the formation of air gaps or stress concentration areas in the casting system. These defects directly cause the partial discharge of the product to exceed the standard, resulting in a significant reduction in the product qualification rate, which further increases the production cost and production losses of the equipment. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fixing the primary coil of a current transformer, which meets the requirements of miniaturization and intensification of the State Grid, shortens the assembly time, eliminates air gap and interface cracking problems, and significantly improves the product qualification rate.

[0005] To achieve the above objectives, this application proposes a method for fixing the primary coil of a current transformer, comprising: Align the iron core clamp with the outer periphery of the iron core, so that the iron core clamp wraps around the iron core, and then fix the iron core clamp to one of the long sides of the iron core. Using the long side of the other side of the iron core as a reference, the secondary coil is evenly wound around the outside of the long side according to the designed number of turns; The primary coil is wound around the outside of the secondary coil, and the lead wire of the primary coil is reserved with a welding length to the primary conductive sheet; The primary conductive sheet is welded to the bottom outer side of the primary coil. During welding, the position is adjusted simultaneously to ensure that the cross-slot countersunk bolt on the primary conductive sheet fixing seat is coaxial with the elliptical countersunk hole of the diagonal support frame of the iron core clamp. Then, the primary conductive sheet is connected to the lead wire of the primary coil by brazing. Align the upper end of the resin bracket with the cross-slot countersunk bolt on the primary conductive sheet mounting base, rotate the resin bracket to engage the top metal insert with the bolt thread until it is tightened and fixed; then align the lower end of the resin bracket with the elliptical countersunk hole of the support frame, pass the cross-slot countersunk bolt through the countersunk hole and connect it with the bottom metal insert threadedly. At this time, only pre-tighten the bolt to leave room for position adjustment. Slowly move the primary coil along the long axis of the elliptical countersunk hole of the support frame, and monitor the distance between the primary coil and the iron core and the secondary coil with a measuring tool until the designed insulation distance is reached; after confirming that the position is correct, fully tighten the cross-slot countersunk bolts on the support frame to achieve rigid fixation between the resin bracket and the support frame.

[0006] In one embodiment, the support seats on the iron core clamp are symmetrically distributed, with a support frame provided on each of the pair of diagonal support seats, and countersunk holes provided on the support frame.

[0007] In one embodiment, the long axis of the elliptical countersunk hole is reserved for adjustment, which is used to adjust the insulation distance between the primary coil and the iron core and the secondary coil.

[0008] In one embodiment, the top of the cross-slot countersunk bolt does not extend beyond the plane of the mounting base.

[0009] In one embodiment, the resin support is a cylindrical structure, and metal inserts are pre-embedded in the end face of the resin support. The metal inserts have threaded holes that are compatible with cross-slot countersunk bolts.

[0010] In one embodiment, the outer peripheral wall of the metal insert is provided with an annular groove, which is combined with the resin support through a vacuum casting process, so that the resin material fills the annular groove to form a mechanical interlocking structure, and there is no air gap at the joint surface between the metal insert and the resin support.

[0011] In one embodiment, the resin support is made of glass fiber reinforced epoxy resin material.

[0012] In one embodiment, the primary conductive sheet is respectively disposed on both sides of the two sections of the primary coil, and the primary conductive sheet corresponds vertically to the support frame of the iron core clamp.

[0013] In one embodiment, the support base of the iron core clamp is provided with a fixing threaded hole for fixing the overall structure to the external mold base.

[0014] In one embodiment, the iron core clamp has an integrally formed support base on its edge.

[0015] The advantages of the above technical solutions adopted in this invention compared with the prior art are as follows: 1. In this application, the top of the cross-head countersunk bolt does not extend beyond the plane of the mounting base, which not only improves the aesthetics of the structure but, more importantly, avoids interference with the electric field distribution caused by the protruding bolt. Simultaneously, the resin bracket adopts a cylindrical, edgeless structure, which avoids the electric field concentration problem easily generated by metal components, effectively reducing the risk of partial discharge, adapting to high-voltage operating environments, and further enhancing insulation stability. Furthermore, the resin bracket is made of glass fiber reinforced epoxy resin, completely replacing traditional metal rods, eliminating floating potential, eddy current losses, and the risk of point discharge at the source, providing reliable protection for the safe operation of the equipment in high-voltage environments.

[0016] 2. This application employs an elliptical countersunk hole structure on the support frame of the diagonal support seat of the iron core clamp, with sufficient adjustment margin reserved in the long axis direction, allowing for precise adjustment of the insulation distance between the primary coil and the iron core and secondary winding. During actual installation, the bolts can be pre-tightened, and after the primary coil position is adjusted to the optimal state, the bolts can be fully tightened, significantly simplifying the assembly process and effectively saving assembly time.

[0017] 3. Compared with the traditional metal suspension fixing method, the resin bracket of this application is directly fixed to the bottom of the coil, eliminating the need to set a metal frame on the upper part and side wall of the primary coil, which significantly reduces the space occupied by the structure and thus effectively reduces the volume of the casting body, fully meeting the State Grid's technical requirements for the miniaturization and intensification of power equipment.

[0018] 4. In traditional metal suspension fixing methods, air gaps or stress concentrations easily form at the junction of the metal parts and the insulating material during the casting process, leading to increased partial discharge and a lower yield rate. In contrast, the resin support and epoxy casting material in this application have similar coefficients of thermal expansion, resulting in a tighter bond and preventing interface cracking after curing, effectively avoiding casting defects. Furthermore, the resin support is directly fixed to the bottom of the coil, eliminating the need for additional upper or sidewall metal supports. The casting body can closely conform to the outer contour of the coil, reducing unnecessary resin filling and significantly lowering epoxy resin usage. Moreover, the resin support can be mass-produced using compression molding, allowing multiple parts to be formed at once, resulting in high production efficiency. In addition, epoxy resin is cheaper than metal and requires no rust prevention treatment or complex machining, significantly reducing overall manufacturing costs. Attached Figure Description

[0019] Figure 1 Three-view diagram of a primary coil fixing structure based on a resin support; Figure 2 Here are the three views and enlarged views of the iron core clamp; Figure 3 This is a schematic diagram of the resin support structure. Figure 4 Three-view diagram of a primary conductive sheet; Wherein: 1 is the iron core; 2 is the iron core clamp; 21 is the support frame; 22 is the support base; 3 is the cross-slot countersunk bolt; 4 is the metal insert; 5 is the resin bracket; 6 is the primary conductive sheet; 7 is the primary coil; 8 is the secondary coil. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0021] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0022] In the description of this application, it should be understood that the terms "center", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0023] In the description of this application, it should be noted that, unless otherwise expressly 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 mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] Please see Figure 1-4 This embodiment provides a method for fixing the primary coil of a current transformer, including: Assembly of iron core and iron core clamp: Align the iron core clamp with the outer circumference of the iron core so that the iron core clamp completely wraps around the iron core. Then fix the iron core clamp to one long side of the iron core by spot welding or positioning pins to ensure that there is no relative displacement between the iron core clamp and the iron core.

[0025] Secondary coil winding: Using the long side of the other side of the iron core as a reference, the secondary coil is evenly wound around the outside of the long side according to the designed number of turns. During the winding process, the winding tension is controlled to be uniform, ensuring that the coil is neatly arranged and tightly attached to the iron core, without looseness or deviation.

[0026] Primary coil winding: The primary coil is wound around the outside of the secondary coil, ensuring that the windings are neatly arranged, and the lead wire of the primary coil is reserved with the welding length to the primary conductive sheet.

[0027] Primary conductive sheet fixing: Weld the primary conductive sheet to the bottom outer side of the primary coil (the left and right sides of the two coil sections). Adjust the position simultaneously during welding to ensure that the cross-slot countersunk bolts on the primary conductive sheet fixing seat are coaxial with the elliptical countersunk holes of the diagonal support frame of the iron core clamp. Then, connect the primary conductive sheet to the lead wire of the primary coil by brazing to complete the construction of the conductive path.

[0028] Pre-connection of resin bracket: Align the upper end of the resin bracket with the cross-slot countersunk bolt on the primary conductive sheet fixing seat, rotate the resin bracket to engage the top metal insert with the bolt thread until it is tightened and fixed; then align the lower end of the resin bracket with the elliptical countersunk hole of the support frame, pass the cross-slot countersunk bolt through the countersunk hole and connect it with the bottom metal insert threadedly. At this time, only the bolt needs to be pre-tightened (not fully tightened) to leave room for position adjustment.

[0029] Insulation distance adjustment and final fixation: Slowly move the primary coil along the long axis of the elliptical countersunk hole of the support frame, and monitor the distance between the primary coil and the iron core and the secondary coil with a measuring tool (such as a vernier caliper) until the designed insulation distance is reached; after confirming that the position is correct, fully tighten the cross-slot countersunk bolts on the support frame to achieve rigid fixation of the resin bracket and the support frame.

[0030] Fixing the entire structure to the mold: Align the positioning holes of the external mold base with the fixing threaded holes of the four support seats of the iron core clamp, and use bolts to fix the entire structure to the mold base through the threaded holes to complete the entire assembly process.

[0031] The above method is achieved through a primary coil fixing structure, which includes: The core clamp is made of steel plate through stamping and integral forming, forming a frame structure that wraps around the outer periphery of the core and makes close contact with it, ensuring stable installation and improving heat dissipation efficiency. Four rectangular, symmetrically distributed support seats are integrally formed along its edge, each with threaded holes for fixing the entire structure to the external mold base. A pair of diagonally opposite support seats have support frames with elliptical countersunk holes at their tops, allowing for precise adjustment of the insulation distance between the primary coil and the core, and between the primary and secondary coils.

[0032] The primary conductive sheet, made of copper sheet and tin-plated to improve conductivity and corrosion resistance, is fixed to the outer bottom of the primary coil by welding. It is positioned on the left and right sides of both sections of the primary coil, providing balanced support. A mounting base is welded to the primary conductive sheet, and countersunk bolts with Phillips head grooves are welded to the mounting base. After welding, the bolt tip must not exceed the plane of the mounting base to avoid the formation of a sharp point effect in the electric field. Simultaneously, the primary conductive sheet is also brazed to the leads of the primary coil, serving the dual functions of "conductive connection" and "structural support."

[0033] The resin support is made of glass fiber reinforced epoxy resin material through compression molding, forming a cylindrical structure without sharp edges. Its axial length is designed according to the voltage transformer specifications, combining high strength and high insulation performance. Furthermore, its coefficient of thermal expansion is close to that of epoxy castable, preventing interface cracking caused by temperature changes. Metal inserts are pre-embedded on both its upper and lower ends. The outer peripheral wall of the metal insert has an annular groove, which is bonded to the resin support through a vacuum casting process. The resin material fills the annular groove, forming a mechanical interlocking structure that ensures no air gaps at the joint surface, effectively reducing the risk of partial discharge. The metal insert has internal threads, with a thread specification compatible with Phillips head countersunk bolts, used to connect the resin support to the primary conductive sheet and support frame.

[0034] The components are assembled stably through a "layered positioning and step-by-step fixing" method, as detailed below: The upper end of the resin bracket is connected to the cross-slot countersunk bolt welded to the primary conductive sheet fixing seat through the internal thread of the top metal insert, so as to achieve rigid fixation with the primary coil. The lower end of the resin bracket: It is connected to the cross-slot countersunk bolt that passes through the elliptical countersunk hole of the support frame via the internal thread of the bottom metal insert, so as to achieve a detachable connection with the iron core clamp. The primary coil is suspended and fixed in the preset position of the iron core by the axial force of the cross-slot countersunk bolts. At the same time, the insulation properties of the resin bracket block the eddy current path, eliminating the risk of floating potential and tip discharge.

[0035] The aforementioned primary coil fixing method based on resin brackets has many advantages, such as convenient installation, stable insulation, compact structure, and reduced cost. It provides an innovative solution for the design of fully insulated voltage transformers and can be widely used in the State Grid's power transmission and distribution network, thereby improving the design and manufacturing level of fully insulated voltage transformers.

[0036] The advantages of this implementation method are: Excellent insulation performance: The round cylindrical structure of the resin bracket without sharp edges, the flush design of the countersunk bolts, and the insulation properties of glass fiber reinforced epoxy resin effectively avoid the risks of electric field concentration and partial discharge, making it suitable for high-voltage operating environments. Easy installation and adjustment: The elliptical countersunk hole adjustment margin design allows for quick and precise adjustment of the insulation distance, shortening the assembly time compared to traditional metal suspension structures; Compact structure adapted for miniaturization: The resin bracket directly supports the bottom of the primary coil, eliminating the need for the metal frame on the upper part and side walls of the coil. The volume of the casting body is smaller than that of the traditional structure, which meets the requirements of miniaturization and intensification of the State Grid. Cost and yield optimization: The resin support and epoxy casting material are tightly bonded, with no air gaps or interface cracking issues, resulting in a significant improvement in product yield. At the same time, the cost of resin materials is lower than that of metals, and there is no need for rust prevention treatment or complex machining, thus reducing the overall manufacturing cost.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

Claims

1. A method for fixing the primary coil of a current transformer, characterized in that, include: Align the iron core clamp with the outer periphery of the iron core, so that the iron core clamp wraps around the iron core, and then fix the iron core clamp to one of the long sides of the iron core. Using the long side of the other side of the iron core as a reference, the secondary coil is evenly wound around the outside of the long side according to the designed number of turns; The primary coil is wound around the outside of the secondary coil, and the lead wire of the primary coil is reserved with a welding length to the primary conductive sheet; The primary conductive sheet is welded to the bottom outer side of the primary coil. During welding, the position is adjusted simultaneously to ensure that the cross-slot countersunk bolt on the primary conductive sheet fixing seat and the elliptical countersunk hole of the diagonal support frame of the iron core clamp are coaxial. Then, the primary conductive sheet and the lead wire of the primary coil are connected by brazing. Align the upper end of the resin bracket with the cross-slot countersunk bolt on the primary conductive sheet mounting base, rotate the resin bracket to engage the top metal insert with the bolt thread until it is tightened and fixed; then align the lower end of the resin bracket with the elliptical countersunk hole of the support frame, pass the cross-slot countersunk bolt through the countersunk hole and connect it with the bottom metal insert threadedly. At this time, only pre-tighten the bolt to leave room for position adjustment. Slowly move the primary coil along the long axis of the elliptical countersunk hole of the support frame, and monitor the distance between the primary coil and the iron core and the secondary coil with a measuring tool until the designed insulation distance is reached; after confirming that the position is correct, fully tighten the cross-slot countersunk bolts on the support frame to achieve rigid fixation between the resin bracket and the support frame. The above method is achieved through a primary coil fixing structure, which includes: The iron core clamp wraps around the outer periphery of the iron core and is in close contact with the iron core; the edge of the iron core clamp has integrally formed support seats that are symmetrically distributed in a rectangle, and each support seat has a fixed threaded hole; a pair of diagonally opposite support seats are provided with support frames, and the top of the support frame has an elliptical countersunk hole with an adjustment allowance reserved along the long axis. A primary conductive sheet is fixed to the bottom outer side of the primary coil; a mounting base with an upward protrusion is stamped on the primary conductive sheet, and a cross-slot countersunk bolt is welded to the mounting base; the primary conductive sheet is also connected to the lead wire of the primary coil by brazing. The resin bracket has metal inserts embedded in both its upper and lower ends. The outer peripheral wall of the metal insert has an annular groove, which is combined with the resin bracket through a vacuum casting process. The metal insert has an internal thread, the thread specification of which is compatible with the cross-slot countersunk bolt, which is used to connect the resin bracket with the primary conductive sheet and the support frame.

2. The method for fixing the primary coil of a current transformer according to claim 1, characterized in that, The top of the cross-grooved countersunk bolt does not exceed the plane of the fixing seat.

3. The method for fixing the primary coil of a current transformer according to claim 1, characterized in that, The resin support is made of glass fiber reinforced epoxy resin material.

4. The method for fixing the primary coil of a current transformer according to claim 1, characterized in that, The primary conductive plates are respectively disposed on both sides of the two sections of the primary coil, and the primary conductive plates are vertically aligned with the support frame of the iron core clamp.

5. The method for fixing the primary coil of a current transformer according to claim 1, characterized in that, The iron core clamp has an integrally formed support base on its edge.

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