Oil-Immersed vs Dry-Type Transformer: A Decision Matrix
Reviewed by the Fengguang engineering team · Last updated 9 Nov 2026
Oil-immersed or dry-type? Use fire strategy, location, capacity, ambient, noise and maintenance to make the decision, not a generic preference.
The real decision is the site
Oil-immersed transformers use oil for insulation and cooling. They are compact, efficient at higher capacities and usually lower in first cost. Dry-type transformers use cast resin or impregnated insulation, remove the oil fire load and suit indoor rooms. The correct choice depends on where the unit sits and what the fire strategy allows.
When oil-immersed wins
Outdoor sites, industrial yards, higher capacities and projects with access for oil maintenance usually favour oil-immersed. The oil also helps heat rejection in hot climates, provided the tank and radiator are designed for the ambient. Corrosion class and enclosure are project options.
When dry-type wins
Indoor rooms, hospitals, data centres, metro stations and buildings with strict fire requirements favour dry-type. The unit still needs ventilation, clearances and protection; it is not maintenance-free. For dusty or humid rooms, specify filters, IP protection and anti-condensation heaters.
| Criterion | Oil-immersed | Dry-type |
|---|---|---|
| Location | Outdoor / yard | Indoor / fire-sensitive |
| Fire load | Oil present | No oil |
| First cost | Usually lower | Usually higher |
| Heat rejection | Strong | Room-dependent |
| Maintenance | Oil and seals | Cleaning / ventilation |
| Noise | Low | Low, but room matters |
FAQ
Which is better for a data centre?
Dry-type is common because it removes the oil fire load and suits indoor electrical rooms. Confirm the fire strategy, room ventilation and noise limit.
Can oil-immersed be installed indoors?
It can be, but the room needs oil containment, fire separation and ventilation. Many projects choose dry-type instead to simplify the fire case.
Which is cheaper over life?
It depends on capacity, load profile, maintenance and fire protection cost. Compare total owning cost, not just the transformer price.
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