Manufacturing Process of Oil-Immersed Transformers

Oil-immersed transformers are critical components in power distribution systems, known for their efficiency, durability, and ability to handle high voltages. Their construction involves precision engineering and strict adherence to safety standards. Below is a step-by-step overview of their manufacturing process:

1. Core Assembly

The transformer core is the magnetic heart of the device.

• Material Selection: High-grade grain-oriented silicon steel laminations are used to minimize hysteresis and eddy current losses.

• Cutting and Stacking: Steel sheets are cut into precise shapes (E-I or stepped-core designs) and stacked in alternating layers to form the core.

• Insulation: Layers are insulated with varnish or oxide coatings to prevent short circuits.

• Clamping: The core is tightly clamped using non-conductive bolts and brackets to ensure structural stability.

2. Winding Fabrication

Windings conduct electrical energy and are divided into primary (high-voltage) and secondary (low-voltage) coils.

• Conductor Selection: Copper or aluminum conductors are chosen based on cost and performance requirements.

• Winding Process: Conductors are wound around insulating cylinders using automated machines. Paper, Nomex, or epoxy resin acts as inter-layer insulation.

• Insulation Testing: Windings undergo dielectric tests to ensure no short circuits or weak spots.

3. Core-Coil Assembly

The core and windings are integrated:

• The core laminations are carefully opened, and pre-wound coils are placed onto the core limbs.

• Insulating barriers (pressboard or bakelite) are inserted between windings and the core to prevent electrical contact.

• Leads and tap changers (for voltage adjustment) are connected to the windings.

4. Tank Fabrication

The tank houses the core-coil assembly and transformer oil.

• Material: Welded steel or aluminum tanks are fabricated to withstand mechanical stress and corrosion.

• Cooling System: Radiators or corrugated panels are attached to enhance heat dissipation.

• Accessories: Bushings, conservators (oil expansion tanks), and pressure relief devices are installed.

5. Oil Processing

Transformer oil serves as both an insulator and coolant.

• Oil Filtration: Mineral or synthetic oil is purified to remove moisture, gases, and particulates.

• Vacuum Filling: Degassed oil is pumped into the tank under vacuum to eliminate air bubbles.

• Dielectric Testing: Oil samples are tested for breakdown voltage (typically >30 kV) and acidity.

6. Final Assembly

• The core-coil unit is lowered into the tank and secured.

• All connections (bushings, gauges, relays) are sealed to prevent oil leaks.

• The tank is filled with oil until the conservator is half-full to allow for thermal expansion.

7. Testing and Quality Control

• Routine Tests:

• Turns ratio verification

• Insulation resistance measurement

• Load loss and no-load loss tests

• Dielectric strength tests (applying high voltage to windings)

• Type Tests:

• Temperature rise test (operating under full load for 24+ hours)

• Short-circuit withstand test (simulating fault conditions)

8. Painting and Packaging

• The exterior is painted with anti-corrosive coatings.

• Transformers are crated for shipping, with desiccants added to absorb moisture.

Key Advantages of Oil-Immersed Design

• Superior heat dissipation compared to dry-type transformers.

• Longer lifespan due to oil’s protective properties against oxidation.

• Cost-effective for high-power applications (>500 kVA).

Conclusion

The manufacturing of oil-immersed transformers demands meticulous attention to material quality, insulation integrity, and oil purity. Advances in automation and oil treatment technologies continue to enhance their reliability, making them indispensable in modern power grids.

This article provides a concise yet comprehensive overview suitable for technical documentation or educational purposes. Let me know if you need further details on specific stages!