Zhuojin Pipe Fitting Co., LtdDesign and Application of Tees in Transformer Connector Welding
Literature Overview
This paper by Ping Yumin from Baoding Tianwei Baobian Electric Co., Ltd. (published in Transformer, 2013) addresses a specialized application of tee fittings in transformer manufacturing: the design and welding of tees in transformer connector (busbar) assemblies. The paper details the drawing method for tees and the precautions during the drawing process, and reports that through multiple trials, the drawing method was successfully applied to the main busbar, improving weld quality and effectively controlling transformer oil leakage. This work is of practical significance for electrical equipment manufacturers and welding engineers dealing with large-scale copper and aluminum conductor assemblies.
Core Technical Content
Drawing Method for Tees
The drawing method involves forming a tee junction by mechanically deforming a tube or pipe to create a branch opening, followed by welding the branch connection. This method offers several advantages over traditional forging or machining:
- Material continuity: The drawing process maintains the material fiber flow pattern, providing improved mechanical properties in the critical regions.
- Reduced material waste: Compared to forging or machining, the drawing method uses less material, reducing cost and environmental impact.
- Improved dimensional accuracy: The drawing process can achieve tight dimensional tolerances, reducing the need for post-processing.
Welding Process for Transformer Connectors
The welding of tees in transformer connectors requires careful control of the following parameters:
- Material: Typically copper or aluminum busbars with specific conductivity and mechanical properties
- Welding process: TIG (GTAW) welding is preferred for its ability to produce clean, high-quality welds without spatter
- Filler metal: Matching filler metal (e.g., ER4043 for aluminum, ER70S-6 for copper) to ensure electrical continuity and mechanical strength
- Shielding gas: Argon for aluminum, argon-helium mixture for copper, to ensure adequate penetration and arc stability
- Heat input: Carefully controlled to prevent excessive distortion and to maintain material properties
Key Process Parameters
| Parameter | Copper Busbar | Aluminum Busbar |
|---|---|---|
| Welding process | GTAW | GTAW |
| Filler metal | ER70S-6 | ER4043 |
| Shielding gas | Ar + 5% He | Pure Ar |
| Current range | 150-300 A | 200-400 A |
| Travel speed | 3-8 mm/s | 5-12 mm/s |
| Preheat temperature | Not required | 100-150 °C |
| Post-weld treatment | None | None |
Technical Challenges and Solutions
The welding of tees in transformer connectors presents several technical challenges that require careful attention:
Challenge 1: Weld Quality and Oil Leakage Prevention
Transformer oil leakage through weld defects is a critical concern. The paper reports that the drawing method, combined with proper welding technique, significantly improves weld quality and reduces the risk of oil leakage. The key factors for preventing oil leakage are:
- Complete weld penetration to eliminate voids and porosity
- Smooth weld transition to avoid stress concentration points
- Proper weld reinforcement to ensure mechanical strength without creating sharp edges
- Post-weld cleaning to remove flux residues and contaminants
Challenge 2: Material Compatibility
The drawing process can cause work hardening in the material, which may affect the subsequent welding process. For copper and aluminum, work hardening can reduce ductility and increase the susceptibility to cracking during welding. The solution is to implement a proper solution heat treatment cycle after drawing to restore ductility before welding.
Challenge 3: Dimensional Accuracy
The drawing process must achieve tight dimensional tolerances to ensure proper fit-up of the tee components. Any misalignment can result in poor weld quality and increased stress concentrations. The paper emphasizes the importance of precise tooling and careful process control during the drawing operation.
Engineering Practice Application
The application of the drawing method for tees in transformer connectors has been validated through multiple trials. The key findings are:
- Weld quality improvement: The drawing method produces tees with better material continuity, resulting in improved weld quality and reduced defect rates.
- Oil leakage control: The improved weld quality directly translates to better oil leakage prevention, reducing maintenance costs and extending transformer service life.
- Cost efficiency: The drawing method reduces material waste and post-processing requirements, resulting in lower manufacturing costs.
- Production efficiency: The drawing process is faster than forging or machining, improving overall production throughput.
Quality Assurance Measures
To ensure consistent quality of the drawn and welded tees, the following quality assurance measures are recommended:
- Incoming material inspection: Verify the chemical composition and mechanical properties of the copper or aluminum stock
- Process parameter monitoring: Monitor and record all welding parameters (current, voltage, travel speed, gas flow rate)
- Visual inspection: 100% visual inspection of all welds for defects such as porosity, undercuts, and incomplete fusion
- Non-destructive testing: Dye penetrant testing (PT) for surface defects, ultrasonic testing (UT) for internal defects
- Dimensional inspection: Verify critical dimensions (branch diameter, wall thickness, weld reinforcement) using calibrated measuring instruments
- Electrical testing: Measure electrical resistance across the weld to ensure adequate conductivity
Study Insights and Practical Recommendations
This paper provides valuable practical guidance for the manufacturing of tee fittings in transformer connectors. The drawing method, when properly executed, offers significant advantages in terms of weld quality, oil leakage prevention, and cost efficiency.
I recommend that transformer manufacturers consider adopting the drawing method for tee production, particularly for high-volume applications where cost efficiency is critical. The key to successful implementation is careful process development and validation, including the optimization of drawing parameters, welding parameters, and quality assurance procedures.
Future work should focus on the automation of the drawing and welding processes to further improve production efficiency and quality consistency. The integration of online monitoring systems for welding parameters and defect detection could provide real-time feedback for process control, reducing the need for offline inspection and rework.