Comprehensive Guide to Oil-Immersed Transformer Materials: From Core to Insulating Oil

Introduction

The performance and lifespan of oil-immersed transformers heavily depend on the quality of their raw materials. This article provides an in-depth analysis of key components, including the core, windings, insulating oil, and tank, along with their pros, cons, and selection criteria.

1. Core Materials: The Heart of the Magnetic Circuit

1.1 Silicon Steel (Electrical Steel)

• Types:
  • Cold-Rolled Grain-Oriented (CRGO): High permeability, low loss (industry standard).
  • Non-Grain-Oriented (CRNGO): Cheaper but less efficient.
• Key Parameters:
  • Core loss (W/kg): Lower is better (premium CRGO: ≤0.9 W/kg).
  • Thickness: 0.23–0.3 mm (thinner = lower eddy current losses).
• Top Brands:
  • Nippon Steel (Japan), Baowu Steel (China), AK Steel (USA).

1.2 Amorphous Metal

• Advantage: 70% lower no-load loss vs. silicon steel.
• Drawbacks:
  • High cost (~2× silicon steel).
  • Brittle, prone to mechanical damage.
• Best For: Ultra-high-efficiency distribution transformers.

2. Winding Materials: Conducting the Current

2.1 Copper Windings

• Pros:
  • High conductivity (low resistance, minimal heat).
  • Mechanically robust, long lifespan.
• Cons: Expensive (30–40% of transformer cost).

2.2 Aluminum Windings

• Pros:
  • Low cost (~1/3 the price of copper).
  • Lightweight (ideal for large transformers).
• Cons:
  • Higher resistance (requires larger cross-sections).
  • Complex welding requirements.

Selection Tip:

• Power Transformers: Prioritize copper (efficiency + longevity).
• Budget Projects: Aluminum (if manufacturing quality is assured).

3. Insulating Oil: Cooling & Insulation

3.1 Mineral Oil (Most Common)

• Pros: Affordable, stable performance.
• Cons: Low flash point (~160°C), non-biodegradable.

3.2 Synthetic Ester Oil

• Pros:
  • High flash point (>300°C).
  • Biodegradable (eco-friendly).
• Cons: 3–5× more expensive than mineral oil.

3.3 Silicone Oil

• Pros: Heat-resistant (>200°C), chemically inert.
• Cons: High viscosity, poor flow.

Selection Tip:

• General Use: Mineral oil (best cost-performance).
• High-Safety Needs: Synthetic ester (e.g., subways, data centers).

4. Tank & Structural Materials

4.1 Tank Material

• Carbon Steel: Economical, requires anti-corrosion coating.
• Stainless Steel: Corrosion-resistant, longer lifespan (ideal for humid/chemical environments).

4.2 Sealing Materials

• Nitrile Rubber (NBR): Oil-resistant, cost-effective.
• Fluorocarbon Rubber (FKM): High-temperature resistant (-40°C–200°C), longer-lasting.

5. Other Critical Materials

6. How Materials Impact Performance

✅ Efficiency: Silicon steel quality determines no-load loss.
✅ Lifespan: Copper windings + synthetic ester oil → 30+ years.
✅ Eco-Friendliness: Biodegradable oil + lead-free solder (RoHS compliant).

7. Procurement Tips: Choosing Quality Materials

1. Core: Demand core loss test reports from suppliers.
2. Insulating Oil: Verify breakdown voltage (>50 kV) and acid value (<0.01 mg KOH/g).
3. Windings: Require ≥99.95% copper purity (test reports mandatory).

Red Flags:
❌ Cheap silicon steel may be recycled (poor magnetic properties).
❌ Low-grade oil oxidizes quickly (replacement needed within 2 years).

Conclusion

Oil-immersed transformer materials directly affect efficiency, lifespan, and safety. Where budget allows, prioritize high-grade silicon steel, copper windings, and synthetic ester oil to reduce long-term costs.