66 kV Substation: How to Select a High-Efficiency Oil-Immersed Transformer with the Lowest Budget

Time：2025-11-25    Auther：ZTelec-www.ztelectransformer.com

When planning a new 66 kV substation or upgrading an existing one, the oil-immersed transformer is often the primary choice due to its excellent cooling performance and strong overload capacity. As one of the largest investment items and the core equipment affecting overall system performance, choosing the right transformer becomes critical. Many project managers struggle to balance high efficiency with cost control. In reality, the “lowest budget” does not mean choosing the cheapest product, but selecting a transformer—with emphasis on oil-immersed models—that offers the lowest total cost of ownership (TCO) over its lifecycle.

This article explains how to select a high-efficiency and cost-effective oil-immersed transformer for a 66 kV substation, especially when project budgets are limited.

Understanding the True Cost of a Transformer

A transformer’s total cost includes more than the initial purchase (CAPEX). Operating costs (OPEX) over the next 20–30 years—primarily caused by electrical losses—often exceed the purchase price. These losses are divided into two categories:

No-load loss (iron loss): Constant energy loss that persists whenever the transformer is energized. It is influenced by the material and processing quality of the iron core.

Load loss (copper loss): Loss that varies with load current and is linked to conductor resistance and winding design.

Key Factors that Determine Transformer Energy Efficiency

1. Core Material

Using advanced core materials significantly reduces energy loss in both dry-type and oil-immersed transformers:

Amorphous alloy core: Reduces no-load losses by 60–70%. Ideal for areas with low load rates or long energization periods.

High-quality grain-oriented silicon steel: Achieves a balance of cost and performance, widely used in economical high-efficiency oil immersed transformer designs.

2. Coil Conductors

High-conductivity copper windings effectively reduce load losses. For large-capacity oil-immersed transformers, increasing the cross-sectional area further improves efficiency and reduces heat generation.

3. Oil and Cooling System Design

Optimized cooling channels and improved heat dissipation are especially essential in oil-immersed transformers. A well-designed oil circulation system reduces hot-spot temperature rise, protects insulation, and extends service life. High-efficiency oil immersed transformers often achieve 20–35% lower lifetime costs than standard models—especially beneficial for 66 kV substations requiring long-term continuous operation.

Practical Transformer Selection Tips for Limited Budgets

1. Prioritize High-Performance Core Materials

If budget allows, amorphous alloy oil-immersed transformers offer the greatest long-term savings by reducing no-load losses by 60–80%. They are especially cost-effective for substations with low load factors or long operation hours.

If amorphous alloy units exceed budget, choosing a Grade 1 energy-efficiency silicon steel oil-immersed transformer still delivers excellent performance at a lower price point.

2. Determine Capacity Accurately

Select transformer capacity based on accurate load forecasts and growth expectations. Oversized oil-immersed transformers operate at low load ratios, leading to high no-load loss percentages and reduced efficiency.

Working closely with engineers and using dynamic load analysis ensures optimal sizing, reducing both procurement cost and operational losses.

3. Compare Technical Solutions to Reduce TCO

Oil-immersed vs. dry-type: For 66 kV substations, oil-immersed transformers offer superior heat dissipation, higher capacity, better insulation performance, and lower overall TCO, making them the mainstream choice.

Two-winding vs. three-winding: If no multi-voltage or special reliability requirements exist, two-winding oil immersed transformers provide lower cost, simpler structure, and reduced losses.

Domestic leading brands vs. international brands: Many top domestic manufacturers now offer high-efficiency oil-immersed transformers comparable to international brands in performance and reliability but at more competitive pricing. Including them in bidding can significantly reduce procurement costs.

Conclusion: High-Efficiency Oil-Immersed Transformers Help You Save More

In 66 kV substation projects, the most economical solution is not the lowest-priced product, but the oil-immersed transformer that delivers the lowest long-term cost. To achieve true cost efficiency:

Choose appropriate materials and structures rather than the most expensive brand.

Control both no-load and load losses through optimized design.

Reduce unnecessary customization and focus on essential functions.

Evaluate long-term operational costs instead of only initial CAPEX.

A high-efficiency oil-immersed transformer typically recovers its additional cost through energy savings within 3–5 years, becoming the best investment for any limited-budget 66 kV substation project.