How to Reduce Core Loss in Oil-Immersed Transformers?

Core loss (or no-load loss) is a critical efficiency parameter in oil-immersed transformers tore, directly impacting energy consumption and operational costs. These losses primarily consist of hysteresis loss and eddy current loss, generated due to alternating magnetic flux in the transformer core.

1. Understanding Core Loss in Transformers
A. Types of Core Loss
Hysteresis Loss

Caused by magnetic domain realignment in the core material.

Depends on core material properties and magnetic flux density (B).

Eddy Current Loss

Induced circulating currents in the core laminations.

Reduced by thinner laminations and high-resistance core materials.

B. Impact of Core Loss
Increases operating temperature, reducing insulation life.

Lowers energy efficiency, leading to higher electricity costs.

May cause localized hot spots, accelerating aging.

2. Key Methods to Reduce Core Loss
A. Optimize Core Material Selection

Best Choice:

Hi-B CRGO steel offers the best balance of cost and performance.

Amorphous cores are ideal for ultra-high-efficiency transformers (e.g., smart grids).

B. Use Thinner & Insulated Laminations
Thinner laminations (0.23mm - 0.30mm) reduce eddy currents.

Insulated coatings (C3, C5, or C6 grades) minimize interlamination shorting.

C. Improve Core Design & Stacking
Step-Lap Jointing

Reduces air gaps and flux leakage at joints.

Lowers magnetizing current and hysteresis loss.

Mitred Corners (45° cuts)

Improves magnetic flux flow, reducing localized losses.

Optimal Core Geometry

Circular or stepped cores minimize flux path length.

D. Reduce Flux Density (B) in Design
Operating at lower flux density (1.5T - 1.7T instead of 1.8T) reduces hysteresis loss.

Trade-off: Requires larger core size, increasing material cost.

E. Precision Manufacturing & Assembly
Tight clamping pressure prevents vibration and interlaminar gaps.

Avoid mechanical stress during cutting/stacking to preserve magnetic properties.

Laser-scribed cores improve magnetic domain alignment.

F. Use High-Quality Transformer Oil
Low-viscosity, high-thermal-conductivity oil improves cooling.

Oxidation inhibitors prevent sludge formation, maintaining efficiency.

G. Operational Best Practices
Avoid overvoltage conditions (increases core loss exponentially).

Regular oil testing (DGA, moisture content) to prevent insulation degradation.

Load transformers optimally (core loss is constant, but efficiency improves with load).

3. Advanced Techniques for Core Loss Reduction
A. Nano-Crystalline Cores (Future Trend)
Lower loss than amorphous metals (~0.1 W/kg).

Higher saturation flux density (1.2T) than Metglas.

B. AI-Assisted Core Loss Prediction
Machine learning models optimize core design before manufacturing.

C. Hybrid Core Materials
Combining CRGO with amorphous alloys for cost-performance balance.

4. Case Study: Core Loss Reduction in a 50MVA Transformer

Key Takeaway:

Material upgrade + design improvements significantly cut losses.

5. Conclusion & Recommendations
Summary of Best Practices
Use Hi-B CRGO steel for balanced cost and performance.
Thinner laminations (0.23mm-0.30mm) with insulation coating.
Optimize core geometry (step-lap joints, mitred corners).
Control flux density (1.5T-1.7T) to minimize hysteresis loss.
Precision manufacturing to avoid mechanical stress.
High-quality transformer oil for better cooling.

Final Recommendation
For new transformers, invest in Hi-B CRGO + step-lap design.
For existing transformers, ensure proper maintenance and oil quality.

By implementing these strategies, manufacturers and operators can enhance efficiency, reduce energy costs, and extend transformer lifespan.

Future Outlook:

Amorphous/nano-crystalline cores may dominate next-gen high-efficiency transformers.

Digital twin technology will enable real-time core loss monitoring.