Dry-type transformers are widely used in modern electrical power systems due to their fire resistance, environmental safety, and minimal maintenance requirements. Among the core components, the manufacturing quality of the transformer coil directly determines the product’s electrical performance, insulation level, and operational reliability. This article presents a comprehensive overview of the manufacturing process for dry-type transformer coils, with emphasis on process flow, key technologies, and quality control methods.
1. Material Preparation: Foundation of Quality Coil Manufacturing
The manufacturing process begins with strict selection of raw materials. High-purity electrolytic copper or aluminum conductors are used for the winding, depending on the design requirements. Insulation materials such as NOMEX, epoxy resin, or fiberglass are prepared in advance according to temperature resistance standards. All materials must comply with IEC or ANSI insulation grades and flame-retardant properties.
2. Coil Winding Process
The coil winding stage is critical to determine the electrical and mechanical integrity of the transformer. Using computer-controlled automatic winding machines, conductors are wound into cylindrical or oval shapes with precise tension and layer alignment. This ensures the required number of turns, uniform distribution, and adequate creepage distance between windings. Common winding methods include foil winding and wire winding, depending on current capacity and voltage grade.
3. Insulation Layering and Interlayer Treatment
Each layer of winding is separated by high-quality insulation materials. During the process, layer-to-layer insulation is enhanced with epoxy-impregnated fiberglass tape or pre-impregnated composite sheets. The insulation system must prevent partial discharge, resist thermal aging, and maintain dielectric strength under load fluctuations.
4. Vacuum Pressure Impregnation (VPI) or Vacuum Casting
Depending on the design type, dry-type transformer coils undergo either vacuum pressure impregnation (VPI) or full vacuum casting. In VPI, the wound coils are immersed in a tank filled with epoxy or polyester resin. Under vacuum and pressure, the resin penetrates voids and bonds all winding layers. For cast resin transformers (e.g., SCB series), the entire coil is cast with epoxy resin in a mold and cured at high temperature. This forms a solid, void-free structure with high mechanical strength and excellent moisture resistance.
5. Curing and Post-Processing
After impregnation or casting, the coil is moved to a curing oven where it is baked at controlled temperatures to solidify the resin. This step determines the final bonding, hardness, and dimensional stability of the coil. Once cured, excess resin is removed and the coil is inspected for cracks, air bubbles, or deformation. In some designs, UV-resistant coatings or protective varnishes are applied to enhance durability.
6. Quality Control and Testing
Strict testing is conducted at every production stage to ensure compliance with electrical, thermal, and mechanical performance standards. Routine tests include:
– Winding resistance measurement
– Insulation resistance testing
– Partial discharge test (must be less than 10 pC)
– Induced overvoltage and power frequency withstand test
– Visual inspection for mechanical defects
Advanced facilities may also use X-ray or ultrasonic equipment to detect internal air pockets or delamination in cast coils.
7. Final Assembly and Packaging
After quality approval, the coils are assembled with core laminations, terminals, temperature sensors, and enclosures. Temperature control devices like PT100 sensors are embedded inside the windings. The complete assembly is mounted on vibration-dampening frames and packaged for transport with moisture-resistant and shock-proof materials.
8. Technical Highlights and Innovation Trends
Modern dry-type transformer coil manufacturing incorporates smart monitoring elements and robotic automation. Some notable innovations include:
– Use of nanocomposite insulation materials with superior thermal conductivity
– Real-time curing control using IoT-enabled sensors
– AI-driven winding precision monitoring systems
– Environment-friendly, halogen-free resin compounds
These advancements help manufacturers meet evolving industry standards like IEC 60076-11 and ANSI C57, as well as regional certifications such as UL and CE.
Dry-type transformer coil manufacturing is a complex process requiring precision, advanced materials, and rigorous quality control. From conductor selection to final assembly, each step is critical to ensuring the transformer's reliability and long-term operation. By understanding the complete process and applying cutting-edge technologies, manufacturers can deliver high-performance dry-type transformers that meet the demands of global energy systems.
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