A method for manufacturing a low-voltage lead of a transformer

Abstract

The present application relates to a kind of transformer low voltage lead manufacturing method, belong to generator transformer technical field.The technical scheme is: copper braided wire is inserted into copper sleeve and marked line, then copper sleeve and braided wire assembly are placed into hydraulic press mold center position, slowly pressurized to set pressure and keep for a certain time, ensure that metal is fully deformed and tightly combined;Tin is plated on the surface of copper plate by hot dipping or electroplating method, the copper braided wire part is wrapped with white cloth tape, and the production of low voltage lead finished product is completed;The beneficial effects of the present application are: the appearance quality of low voltage lead made by cold pressing process is obviously better than that of phosphor copper welding process, and the problem of oxidation foreign matter caused by high temperature welding is completely avoided.The hardness of copper braided wire does not change because the lead is not subjected to high temperature heating and dipping water cooling process, the softness of the overall processed lead is greatly improved, and the difficulty of low voltage lead bending installation is reduced.

Description

Technical Field

[0001] This invention relates to a method for manufacturing low-voltage leads of a transformer, belonging to the technical field of manufacturing low-voltage high-current leads for generator transformers. Background Technology

[0002] The low-voltage, high-current leads of AC generator transformers employ a structure where connecting plates are welded to multiple copper braided wires. This requires numerous processes, including cutting, sorting, bundling, shaping, welding, grinding, cleaning, and tin plating. The process is complex and inefficient. The high temperatures during welding cause oxides, such as copper oxide, to form on the surface and in the interlayer of the copper braided wires. These oxides are difficult to remove completely, and residual oxides can lead to decreased conductivity, localized overheating, and foreign object contamination, among other quality issues. Furthermore, the numerous manual steps result in inconsistent process quality and significant fluctuations in product quality. The specific manufacturing method is as follows: (1) Cut the wires according to the dimensions required by the drawing. See attached document Figure 1 , 2 For products with large capacity, the number of copper braided wires 1 in a single lead is large. Due to the limitation of the width of the connector, the width of the multiple copper braided wires after being arranged exceeds the width of the connector, which cannot meet the welding requirements. Therefore, for this type of structure, it is necessary to hammer and shape the single copper braided wire in advance to reduce the size of the single copper braided lead; (2) sorting See attached document Figure 3 , 4 After shaping, the single copper braided wires are arranged and combined, and then tied tightly with copper wire 2. The specific tying size is controlled according to the overlap size between the copper braided wire and the connector. After tying, the wires are hammered and shaped. (3) Binding and welding See attached document Figure 5 , 6 After the copper braided wire is tied and shaped, it is welded using copper welding machine 3; (4) Polishing, cleaning, and tin plating See attached document Figure 7 , 8 After welding, the parts are polished and cleaned, and the connector 5 is outsourced for tin plating 6.

[0003] During the aforementioned welding process, a large amount of oxide 4 is formed and adheres to the surface of the lead wires and within the interlayer, requiring repeated tapping and vibration to clean the lead wires. However, due to the large number of lead wires and the fine and dense copper braided wire, it is impossible to guarantee that all foreign matter trapped inside can be completely cleaned. The lead wires are wrapped with white cloth tape, but after the device dries, oxide often overflows from the lead wire surface, causing contamination and posing a significant quality risk to the product. Figure 9 , Figure 10 As shown.

[0004] Taking an SFP-800000 / 500 product as an example, the low-voltage connector has 8 leads per phase, totaling 24 leads across three phases. Following the above process, the initial fabrication, wiring, and organization require 6 people and 2 days. After the leads are bound and welded to both ends (48 connectors), 2 people and 3 days are needed. Rust removal after welding takes 2 people and 1 day. After rust removal, the product is transferred to an external supplier for tin plating. After tin plating, it undergoes a 48-hour drying process. Because the leads are continuously sprayed with water for cooling during welding, the moisture inside the copper braided wire evaporates slowly, making it difficult to clean foreign objects trapped inside. After drying, the leads are cleaned, and then insulated, requiring 6 people and 1 day. The entire lead processing cycle takes approximately 10 days and requires a significant investment of manpower.

[0005] To address the risks of oxide residue, improve product quality and reliability, simplify the process, reduce labor costs, and increase production efficiency, an optimized process method for manufacturing low-voltage leads for transformers has been invented. Summary of the Invention

[0006] The purpose of this invention is to provide a method for manufacturing low-voltage leads of transformers, which can greatly improve the appearance quality of low-voltage leads, avoid the generation of foreign objects, and solve the problems existing in the background art.

[0007] The technical solution of this invention is: A method for manufacturing low-voltage leads for a transformer, comprising the following steps: Step 1: Measure the required length of copper braided wire according to the design drawings and cut it accordingly; Step 2: Before making a single low-voltage lead, first determine the type, cross-sectional area, and number of copper braided wires to be used, and calculate the total cross-sectional area. Step 3: Based on the length and width of the bushing oil-side terminal block of the transformer, and in conjunction with the transformer model, determine the key dimensions of the terminal blocks. The cross-sectional area of ​​the copper bushing must match the total cross-sectional area of ​​the copper braided wire. Step 4: Wipe the inner and outer surfaces of the copper sleeve and the surface of the copper braided wire to remove oil, oxide film and dust, and insert the copper braided wire into the copper sleeve; Step 5: Use a marker to draw a clear mark line along the circumference at the end where the copper braided wire is inserted into the copper sleeve. The mark position should accurately correspond to the designed insertion depth. After the copper sleeve and copper braided wire are crimped together, check whether the above mark has shifted. Step Six: Place the copper sleeve and braided wire assembly into the center of the hydraulic press mold, slowly apply pressure to the set pressure and hold for a certain time to ensure that the metal is fully deformed and tightly bonded; Step 7: Trim the edges of the copper sleeve to remove burrs and flash caused by crimping, and ensure that the length and width are consistent with the sleeve terminal block; Step 8: Drill holes at the designated locations according to the drawings; Step 9: Apply tin plating to the surface of the copper plate using hot-dip tin plating or electroplating. The plating thickness should be uniform and meet the design requirements. Step 10: Wrap the copper braided wire with white cloth tape to complete the production of the low-voltage lead wire; Step 11: Use a DC resistance tester to test the finished low-voltage lead wires. The measurement results should meet the relevant standards and design values. Step 12: Conduct a tensile test on the finished low-voltage lead wire using a tensile testing device; Step 13: Conduct a visual inspection of the finished low-voltage lead wires; Step Fourteen: Install the qualified low-voltage leads onto the transformer body.

[0008] Furthermore, in step three: the cross-sectional area of ​​the copper braided wire is greater than 60% of the cross-sectional area of ​​the copper sleeve.

[0009] Furthermore, in step four: for leads with a large cross-sectional area and a large number of leads, the copper sleeve can be pre-pressed and shaped to form a groove in the inner hole that matches the shape of the wire bundle.

[0010] Furthermore, in step five, the allowable error for the mark displacement is no more than 3 mm.

[0011] Furthermore, in step eight, the error between the borehole diameter and the hole spacing must be controlled within ±0.1 mm.

[0012] The beneficial effects of this invention are as follows: the appearance quality of low-voltage leads manufactured using the cold-pressing process is significantly better than that of leads manufactured using the phosphor bronze welding process, completely avoiding the oxidation and foreign matter problems caused by high-temperature welding. Simultaneously, because the leads do not undergo high-temperature heating and water-cooling processes, the hardness of the copper braided wire remains unchanged, greatly improving the overall flexibility of the formed leads and reducing the difficulty of bending and installing low-voltage leads. This improves product quality stability and significantly increases work efficiency. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a broken lead wire in the background technology. Figure 2 This is a schematic diagram of lead shaping in the background technology. Figure 3 Background: Schematic diagram of copper wire binding; Figure 4 This is a schematic diagram of copper wire shaping in the background technology. Figure 5 This is a schematic diagram of copper wire after shaping, as shown in the background technology. Figure 6 This is a schematic diagram of phosphorus copper welding in the background technology. Figure 7 This is a schematic diagram of lead wire cleaning and polishing in the background technology. Figure 8 Background technology: Schematic diagram of lead tin plating; Figure 9 This is a schematic diagram of the lead surface after drying in the background technology. Figure 10 This is a schematic diagram of foreign matter contamination on the surface of the lead wire after drying, as shown in the background technology. Figure 11 This is a schematic diagram of the external shape of the copper sleeve after crimping according to the present invention; Figure 12 This is a schematic diagram of the copper braided wire inserted into the copper tube according to the present invention; Figure 13 This is a schematic diagram of the copper tube crimping process of the present invention; Figure 14 This is a schematic diagram of the milling process of the present invention; Figure 15 This is a schematic diagram of the low-voltage lead wire of the finished product of this invention; Figure 16 This is a schematic diagram of the direct resistance test of the present invention; Figure 17 This is a schematic diagram of the tensile test of the present invention; Figure 18 This is a schematic diagram of the invention installed on the device body; In the diagram: 1. Copper braided wire; 2. Copper wire; 3. Copper welding machine; 4. Oxide; 5. Connecting piece; 6. Tin plating; 7. Copper sleeve; 8. Hydraulic press; 9. Mold; 10. CNC milling machine; 11. White cloth tape; 12. DC resistance tester; 13. Low-voltage lead wire finished product; 14. Tensile testing equipment; 15. Transformer body. Detailed Implementation

[0014] The invention will be further described below with reference to the accompanying drawings and examples.

[0015] See attached document Figure 11-18 A method for manufacturing low-voltage leads for a transformer, comprising the following steps: Step 1: Measure the required length of copper braided wire according to the design drawings and cut it accordingly; Step 2: Before making a single low-voltage lead, first determine the type, cross-sectional area, and number of copper braided wires to be used, and calculate the total cross-sectional area. Step 3: Based on the length and width of the bushing oil-side terminal block of the transformer, and in conjunction with the transformer model, determine the key dimensions of the terminal blocks. The cross-sectional area of ​​the copper bushing must match the total cross-sectional area of ​​the copper braided wire. Step 4: Wipe the inner and outer surfaces of the copper sleeve and the surface of the copper braided wire to remove oil, oxide film and dust, and insert the copper braided wire into the copper sleeve; Step 5: Use a marker to draw a clear mark line along the circumference at the end where the copper braided wire is inserted into the copper sleeve. The mark position should accurately correspond to the designed insertion depth. After the copper sleeve and copper braided wire are crimped together, check whether the above mark has shifted. Step Six: Place the copper sleeve and braided wire assembly into the center of the hydraulic press mold, slowly apply pressure to the set pressure and hold for a certain time to ensure that the metal is fully deformed and tightly bonded; Step 7: Trim the edges of the copper sleeve to remove burrs and flash caused by crimping, and ensure that the length and width are consistent with the sleeve terminal block; Step 8: Drill holes at the designated locations according to the drawings; Step 9: Apply tin plating to the surface of the copper plate using hot-dip tin plating or electroplating. The plating thickness should be uniform and meet the design requirements. Step 10: Wrap the copper braided wire with white cloth tape to complete the production of the low-voltage lead wire; Step 11: Use a DC resistance tester to test the finished low-voltage lead wires. The measurement results should meet the relevant standards and design values. Step 12: Conduct a tensile test on the finished low-voltage lead wire using a tensile testing device; Step 13: Conduct a visual inspection of the finished low-voltage lead wires; Step Fourteen: Install the qualified low-voltage leads onto the transformer body.

[0016] In this example, refer to the appendix. Figure 11-18 The specific method is as follows: 1. Accurately measure the required length of copper braided wire according to the design drawings, and cut it using dedicated wire cutters. The cut must be vertical and flat, without burrs or bevels, otherwise it will affect the tightness of subsequent crimping and conductivity. After cutting, each copper braided wire should be arranged separately to avoid tangling.

[0017] 2. Before fabricating a single low-voltage lead, the model, cross-sectional area, and number of copper braided wires used must be clearly defined, and the total cross-sectional area must be calculated. Example: For the Qinhuangdao Thermal Power Project product, model: SFP-440000 / 220, factory work number: 202502S28, low-voltage lead. A single low-voltage lead is fabricated from 24 DXTZ-15-95 copper braided wires, with a total conductor cross-sectional area of ​​24 * 95 = 2280 mm². The cross-sectional area calculation is not only the basis for selecting the copper bushing, but also directly affects the selection of the crimping die, the setting of crimping pressure parameters, and subsequent electrical performance.

[0018] 3. Based on the length and width of the bushing oil-side terminal block, determine the key dimensions of terminal block 5 (L1, L2, L3, L4, L5, L6, m, n, φd) in conjunction with the product model. The cross-sectional area of ​​the copper sleeve 7 must match the total cross-sectional area of ​​the copper braided wire. The cross-sectional area of ​​the copper braided wire must be greater than 60% of the cross-sectional area of ​​the copper sleeve; otherwise, the copper sleeve specification should be reduced. If the cross-sectional area difference is too large, it may lead to loose crimping, increased contact resistance, or even overheating of the leads. See [link to relevant documentation]. Figure 11 .

[0019] 4. Soak a white cloth in anhydrous alcohol and thoroughly wipe the inner and outer surfaces of the copper sleeve 7 and the surface of the copper braided wire 1 to remove oil, oxide film, and dust. For leads with a larger cross-sectional area and more wires, the copper sleeve 7 can be pre-pressed and shaped using a special mold 9 to form a groove in the inner hole that matches the shape of the wire harness, facilitating easy insertion and reducing stress concentration during crimping. See [link to relevant documentation]. Figure 12 .

[0020] 5. Draw a clear marking line along the circumference at the end where the copper braided wire 1 is inserted into the copper sleeve 7. The marking position should accurately correspond to the designed insertion depth. After crimping, check whether the marking has shifted. The allowable error should not exceed 3 mm. Excessive shift may lead to insufficient contact area, causing overheating or a decrease in mechanical strength.

[0021] 6. Adjust the dimensions of the 500 t hydraulic press mold 8 to ensure it matches the bushing terminal block. Place the copper bushing 4 and copper braided wire 1 assembly into the center of the mold 9, slowly apply pressure to the set pressure and hold for a certain time to ensure the metal is fully deformed and tightly bonded.

[0022] Post-crimping inspection: The surface of copper sleeve 7 is free of cracks, dents, or deformation; the copper braided wire 1 is free of broken strands and looseness; the flatness is less than 0.15 mm as measured with a knife-edge ruler; a manual tensile test is performed to confirm there is no looseness. See [link / details]. Figure 13 .

[0023] 7. Use a CNC milling machine 10 or a special milling cutter to trim the edges of the copper sleeve 7, removing burrs and flash caused by crimping, ensuring that the length and width match the sleeve terminal block. The surface roughness must meet the drawing requirements to avoid affecting the sealing performance or causing installation interference. See [reference needed]. Figure 14 .

[0024] 8. Drill holes at the designated locations according to the drawings. The error in hole diameter and hole spacing must be controlled within ±0.1 mm. After drilling, use a special tool to clean burrs and metal shavings from the holes, and rinse with compressed air or alcohol to ensure that the hole walls are smooth and clean, so as to avoid affecting the conductivity and tightness of the bolt connection.

[0025] 9. Tin plating should be performed on the copper plate surface using hot-dip tin plating or electroplating. The plating thickness should be uniform and meet design requirements, typically 5–10 μm. Tin plating effectively reduces contact resistance, improves corrosion resistance, and prevents oxidation. The plating surface should be bright and free of pinholes, peeling, or incomplete plating.

[0026] 10. Wrap the copper braided wire section twice with white cloth tape 11, ensuring the wrapping is smooth, wrinkle-free, and moderately tight. White cloth tape 11 not only provides insulation and protection but also secures the wire and reduces wear from vibration. (See...) Figure 15 .

[0027] 11. Use a DC resistance tester 12 to test the low-voltage lead product 13. The measurement results should meet the relevant standards and design values. If abnormal resistance is found, check for problems such as crimping quality, damage to the copper braided wire, or poor contact, and rework promptly. See [link to relevant documentation]. Figure 16 .

[0028] 12. Use tensile testing equipment 14 to conduct a tensile test on the low-voltage lead wire, requiring it to withstand a tensile load of 7.2kN. After holding the load for 1 minute, observe whether the crimped joint slips, deforms, or breaks. Only after passing the test can the subsequent process proceed. See [link to relevant documentation]. Figure 17 .

[0029] 13. Conduct a comprehensive visual inspection of the finished low-voltage lead wire (13) to ensure that the surface is free of scratches, rust, or plating defects; dimensional re-inspection includes total length, copper sleeve size, hole diameter, and hole spacing, etc., and all data must be recorded and archived. Establish complete production records, including raw material batches, processing parameters, inspection results, etc. Regularly analyze test data, optimize crimping processes and inspection standards, and improve product consistency and reliability; 14. Install the completed low-voltage lead wire 13 onto the transformer body 15, see... Figure 18 .

[0030] The appearance quality of leads produced by the aforementioned cold-pressing process is significantly superior to that produced by phosphor bronze welding. The cold-pressing process completely avoids the oxidation and foreign matter problems caused by high-temperature welding. At the same time, since the leads do not undergo high-temperature heating and water-cooling processes, the hardness of the copper braided wire remains unchanged, and the overall flexibility of the formed leads is greatly improved, reducing the difficulty of bending and installing low-voltage leads.

[0031] The original manufacturing process involved six core steps, including copper wire pretreatment (cutting / bundling), high-temperature welding, post-weld grinding and cleaning, and insulation wrapping. After adjustment and integration, only one insulation wrapping step is required. This frees up 7.5 operators per shift, a reduction of 93.8%, significantly reducing the manpower required for the welding process. All operational steps involved in the phosphor bronze welding process can be reduced. The freed-up human resources can be transferred to the assembly of the transformer body and the overall balance optimization of the transformer manufacturing process, effectively improving production efficiency.

Claims

1. A method for manufacturing low-voltage leads of a transformer, characterized in that: Follow these steps: Step 1: Measure the required length of copper braided wire according to the design drawings and cut it accordingly; Step 2: Before making a single low-voltage lead, first determine the type, cross-sectional area, and number of copper braided wires to be used, and calculate the total cross-sectional area. Step 3: Based on the length and width of the bushing oil-side terminal block of the transformer, and in conjunction with the transformer model, determine the key dimensions of the terminal blocks. The cross-sectional area of ​​the copper bushing must match the total cross-sectional area of ​​the copper braided wire. Step 4: Wipe the inner and outer surfaces of the copper sleeve and the surface of the copper braided wire to remove oil, oxide film and dust, and insert the copper braided wire into the copper sleeve; Step 5: Use a marker to draw a clear mark line along the circumference at the end where the copper braided wire is inserted into the copper sleeve. The mark position should accurately correspond to the designed insertion depth. After the copper sleeve and copper braided wire are crimped together, check whether the above mark has shifted. Step Six: Place the copper sleeve and braided wire assembly into the center of the hydraulic press mold, slowly apply pressure to the set pressure and hold for a certain time to ensure that the metal is fully deformed and tightly bonded; Step 7: Trim the edges of the copper sleeve to remove burrs and flash caused by crimping, and ensure that the length and width are consistent with the sleeve terminal block; Step 8: Drill holes at the designated locations according to the drawings; Step 9: Apply tin plating to the surface of the copper plate using hot-dip tin plating or electroplating. The plating thickness should be uniform and meet the design requirements. Step 10: Wrap the copper braided wire with white cloth tape to complete the production of the low-voltage lead wire; Step 11: Use a DC resistance tester to test the finished low-voltage lead wires. The measurement results should meet the relevant standards and design values. Step 12: Conduct a tensile test on the finished low-voltage lead wire using a tensile testing device; Step 13: Conduct a visual inspection of the finished low-voltage lead wires; Step Fourteen: Install the qualified low-voltage leads onto the transformer body.

2. The method for manufacturing a transformer low-voltage lead according to claim 1, characterized in that: Step 3: The cross-sectional area of ​​the copper braided wire is greater than 60% of the cross-sectional area of ​​the copper sleeve.

3. A method for manufacturing a transformer low-voltage lead according to claim 1 or 2, characterized in that: Step four: For leads with a large cross-sectional area and a large number of leads, the copper sleeve can be pre-pressed and shaped to form a groove in the inner hole that matches the shape of the lead bundle.

4. A method for manufacturing a transformer low-voltage lead according to claim 1 or 2, characterized in that: Step 5: The allowable error for the marked displacement is no more than 3mm.

5. A method for manufacturing a transformer low-voltage lead according to claim 1 or 2, characterized in that: Step eight: The error between the borehole diameter and the hole spacing must be controlled within ±0.1 mm.

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