How to choose between dry-type transformers and oil-immersed transformers

From a cost and technical standpoint, there are several key factors to consider when choosing between dry-type transformers and oil-immersed transformers. Here’s a breakdown of their advantages, disadvantages, and optimal use cases:

1. Cost Considerations

• Dry-Type Transformers: Generally more expensive upfront than oil-immersed transformers. The cost is largely due to the materials and manufacturing processes involved, especially with higher insulation materials like epoxy resins in SCB models. However, dry-type transformers require minimal maintenance, reducing long-term operational costs.
• Oil-Immersed Transformers: Lower initial purchase cost, particularly in larger capacities, due to simpler construction and fewer insulation requirements. However, they can incur higher maintenance costs due to the need for periodic oil testing, filtration, and replacement. Oil handling equipment and spill containment add to operational expenses.

2. Technical Considerations

• Insulation and Cooling:

  • Dry-Type: These transformers use air as the cooling medium, making them ideal for indoor applications where fire safety is crucial. They rely on either natural air or forced-air cooling. The SCB type (resin encapsulated) offers better heat dissipation and is more suited for indoor environments prone to higher ambient temperatures.
  • Oil-Immersed: Oil functions as both an insulating and cooling medium, which allows for better heat dissipation and greater overload tolerance. Oil-immersed transformers are preferred for large power capacities and high-voltage applications due to their efficient cooling and high load-bearing capacity.

• Overload Capability:

  • Dry-Type: These transformers have limited overload capacity, requiring operation close to their rated load to prevent overheating. They are generally not designed for sustained overloads.
  • Oil-Immersed: Can handle short-term overloads, which is particularly useful in applications where load fluctuations are frequent or demand spikes periodically.

• Environmental and Safety Factors:

  • Dry-Type: Ideal for indoor, densely populated, or confined spaces, such as hospitals, commercial buildings, and underground installations. They are also preferred in environments where fire and explosion risks are a concern, as they do not contain flammable oil.
  • Oil-Immersed: Suitable for outdoor and industrial settings, where space constraints are less of an issue. However, the presence of oil introduces risks of leakage, environmental contamination, and fire hazards, so additional precautions like firewalls and spill containment are necessary.

• Operating Conditions:

  • In humid regions, oil-immersed transformers perform better, as the oil provides protection against moisture.
  • In dusty or highly contaminated environments, dry-type transformers may be preferred since they are generally enclosed.

3. Advantages and Disadvantages Summary

4. Conclusion: Choosing Between the Two

For indoor applications or installations in fire-sensitive and space-constrained locations, dry-type transformers are preferred despite the higher cost due to safety and environmental benefits. For outdoor or large-scale power applications with higher load-bearing requirements, oil-immersed transformers offer more economic and technical advantages due to their cost-effectiveness, better cooling, and overload capacity.