Difference between dry type transformer and oil type transformer

1. Appearance & Encapsulation

• Dry-Type Transformers: The iron core and windings are directly visible (no closed tank), with windings typically encapsulated in epoxy resin or wrapped in insulating paper and paint to prevent moisture.
• Oil-Immersed Transformers: Only the outer tank is visible; the iron core and windings are sealed inside the tank filled with insulating oil, completely hidden from view.

2. Insulation & Cooling Systems

• Dry-Type Transformers:
  • Insulation: Uses epoxy resin or special insulating paper + insulating paint.
  • Cooling: Relies on natural air cooling (AN) for small capacities; large-capacity models use forced fan cooling (AF).
• Oil-Immersed Transformers:
  • Insulation: Uses insulating oil as both insulation and cooling medium.
  • Cooling: Insulating oil circulates inside the tank, transferring heat to the tank wall and radiators, then dissipating to the air.

3. Capacity & Voltage Levels

• Dry-Type Transformers: Mostly used in distribution networks with capacity ≤1600kVA, voltage ≤10kV (max ≤35kV), suitable for medium-to-small load scenarios.
• Oil-Immersed Transformers: Supports various capacities and voltage levels (from small distribution to large power transformers, e.g., 220kV/500kV ultra-high voltage), adaptable to large-load and long-distance transmission needs.

4. Applicable Scenarios

• Dry-Type Transformers: Ideal for “fireproof and explosion-proof” occasions, such as large buildings, high-rises, data centers, and indoor power distribution rooms—no oil leakage or fire risks.
• Oil-Immersed Transformers: Mostly used outdoors; oil leakage may cause fires in accidents, so they are not suitable for indoor or fire-sensitive areas.

5. Load Capacity

• Dry-Type Transformers: Usually operate at fixed rated capacity, with limited overload capability.
• Oil-Immersed Transformers: Have excellent overload performance, able to handle short-term overload operation (e.g., 120% rated load) due to efficient oil cooling.

6. Purchase Cost

• Dry-Type Transformers: Significantly higher price than oil-immersed transformers of the same capacity—epoxy encapsulation and fireproof materials increase manufacturing costs.
• Oil-Immersed Transformers: More cost-effective, with lower production costs due to mature oil insulation and cooling technology.

7. Lead-Out Bushing Types

• Dry-Type Transformers: Mostly use silicon rubber bushings, lightweight and moisture-resistant, suitable for indoor environments.
• Oil-Immersed Transformers: Mostly use porcelain bushings, high-temperature resistant and durable, adapting to harsh outdoor conditions (e.g., wind, rain).

8. Core Cooling Medium & Structure

• Dry-Type Transformers: Cooling medium is air or special gases (e.g., SF₆); windings are encapsulated in epoxy resin or insulated with paint/paper.
• Oil-Immersed Transformers: Cooling medium is transformer oil; the core and windings are placed in a sealed tank filled with insulating oil for insulation and heat dissipation.