Energy-Saving Renovation Technologies for High-Loss Power Transformers: Core and Winding Replacement

Iron Loss: Occurs in the transformer core due to hysteresis and eddy currents when exposed to alternating magnetic fields. Traditional cores made of hot-rolled silicon steel sheets (with high magnetic permeability but significant hysteresis loss) are a major contributor.

Copper Loss: Arises from the resistance of winding conductors during current flow. Older transformers often use low-conductivity copper or aluminum windings with larger cross-sections, leading to higher I²R losses, especially under heavy loads.

Design Limitations: Outdated winding layouts (e.g., non-optimized turns ratio) and poor insulation materials further exacerbate losses and reduce heat dissipation efficiency.

Amorphous Alloy Cores: Amorphous alloys (e.g., iron-based alloys with a disordered atomic structure) exhibit extremely low hysteresis loss—approximately 70% lower than traditional cold-rolled silicon steel (CRGO). Their high electrical resistivity also minimizes eddy current loss. However, amorphous alloys are brittle and require careful handling during manufacturing.

High-Grade CRGO Steel: For applications where amorphous alloys are cost-prohibitive, high-grade CRGO steel (e.g., 0.23mm thick with grain orientation) offers 30–40% lower iron loss than older hot-rolled varieties. Its improved magnetic properties ensure efficient flux conduction.

Step-Lap Joint Design: Replacing traditional butt joints with step-lap joints reduces magnetic flux leakage at the core corners, lowering localized losses by 15–20%.

Thinner Laminations: Using 0.18–0.23mm thick laminations (compared to 0.3–0.5mm in old cores) decreases eddy current loss, as thinner layers limit current circulation within individual sheets.

Vacuum Annealing: Post-assembly annealing eliminates residual stress in the core, restoring magnetic permeability and ensuring uniform flux distribution.

High-Conductivity Copper: Oxygen-free high-conductivity (OFHC) copper, with a conductivity of 101% IACS (International Annealed Copper Standard), reduces resistance by 5–10% compared to standard electrolytic copper used in old windings.

Aluminum Alloys: For cost-sensitive applications, aluminum conductors with enhanced conductivity (e.g., AA 1350 alloy) combined with copper cladding (to improve solderability) offer a viable alternative, though their conductivity is ~61% IACS, requiring larger cross-sections than copper.

Multi-Strand Conductors: Using Litz wire (stranded conductors insulated from each other) reduces skin effect and proximity effect losses at high frequencies, critical for transformers serving non-linear loads (e.g., inverters).

Optimal Turns Ratio: Redesigning the turns ratio based on actual grid voltage conditions minimizes no-load losses, especially in transformers operating at voltages deviating from nominal values.

Improved Insulation: Replacing paper or cloth insulation withNomex® or epoxy-impregnated materials enhances thermal stability, allowing higher current densities without overheating.

Loss Calculation: Conduct tests (e.g., short-circuit and open-circuit tests per IEC 60076-1) to quantify current iron and copper losses, establishing a baseline for energy savings.

Mechanical Evaluation: Inspect the transformer tank, bushings, and cooling system to ensure they can accommodate the new core and windings, modifying them if necessary.

Core-Winding Alignment: Precise alignment minimizes leakage flux between the core and windings, reducing stray losses.

Pressure Testing: The renovated transformer undergoes pressure testing (e.g., 0.1MPa for oil-immersed units) to check for oil leaks or gas tightness.

Performance Testing: Post-assembly tests include no-load loss, load loss, and efficiency measurements to verify compliance with targets (e.g., achieving IE3 efficiency class per IEC 60076-12).

Grid Integration: Gradually energize the transformer and monitor parameters (temperature, vibration, loss) under actual load conditions for 1–3 months.

Data Logging: Install smart sensors to track real-time energy consumption, comparing it with pre-renovation data to validate savings.

Energy Efficiency Improvement: Core and winding replacement typically reduces total losses by 40–60%. For a 10MVA high-loss transformer, this translates to annual energy savings of 50,000–150,000 kWh.

Payback Period: Despite renovation costs (20–40% of a new transformer), the payback period is usually 3–7 years, depending on electricity prices and load factors.

Extended Lifespan: Renovated transformers can operate for an additional 15–20 years, deferring the need for new purchases and reducing capital expenditure.

Environmental Impact: Reduced energy consumption lowers carbon emissions—each 100,000 kWh saved corresponds to approximately 50–80 tons of CO₂ reduction annually.

Iron loss reduced from 25kW to 8kW.

Copper loss at full load decreased from 80kW to 45kW.

Annual energy savings: ~120,000 kWh, with a payback period of 4.5 years.

Total losses cut by 52%.

Efficiency improved from 95.2% to 97.8% at 75% load.

Qualified for EU energy efficiency subsidies, shortening the payback period to 3 years.

Technical Risks: Poor core-winding alignment may increase stray losses. Mitigation: Use laser alignment tools during assembly.

Cost Constraints: Amorphous alloy cores are 2–3 times more expensive than CRGO. Mitigation: Opt for hybrid designs (amorphous core with CRGO yokes) to balance cost and performance.

Downtime: Renovation takes 2–4 weeks, disrupting power supply. Mitigation: Schedule work during low-demand periods and use temporary transformers.