Dry type transformers and oil immersed transformers are two common types of transformers, differing significantly in cooling methods, structure, performance, and application scenarios. Here’s a detailed comparison:

1. Cooling Medium & Principle

Dry type Transformer  

   Uses air as the cooling medium. Heat generated by the core and windings is dissipated into the surrounding air through natural convection (AN) or forced air cooling (AF, via fans).  

   No flammable or liquid cooling agents, making it suitable for environments where fire safety is critical.  

Oil immersed Transformer  

   Relies on insulating oil (e.g., mineral oil, synthetic oil) for cooling. The oil absorbs heat from the core and windings, circulates naturally (ONAN) or via pumps (ONAF/ODAF), and releases heat through radiators or cooling fins.  

   The oil also acts as an insulator, enhancing the transformer’s dielectric strength.  

2. Structural Differences

3. Performance & Safety

Fire Risk  

   Dry-type: Low fire risk (no flammable oil); some models are flame-retardant (e.g., epoxy cast).  

   Oil-immersed: Higher fire risk if oil leaks or overheats; requires fireproofing measures (e.g., oil-impermeable trenches).  

Insulation Strength  

   Dry-type: Lower dielectric strength (typically up to 35kV) due to air insulation.  

   Oil-immersed: Higher insulation capacity (suitable for high voltages, 110kV and above) because oil is a better insulator than air.  

Noise Level  

   Dry-type: Generally quieter, especially with low loss designs.  

   Oil-immersed: May produce more noise due to oil circulation and cooling fans/pumps.  

4. Application Scenarios

Dry-type Transformers  

   Indoor environments with strict fire safety requirements: commercial buildings, hospitals, data centers, and factories.  

   Low to medium voltage (up to 35kV) and small to medium capacities.  

Oil immersed Transformers  

   Outdoor installations (e.g., power substations) or areas with ample space.  

   High voltage (110kV+) and large capacity applications (e.g., grid transmission, industrial plants with heavy loads).  

5. Cost & Lifespan

Initial Cost  

   Dry-type: Higher upfront cost (due to advanced insulation materials like epoxy).  

   Oil-immersed: Lower initial cost for large capacities.  

Lifespan & Maintenance  

   Dry-type: Longer lifespan (20–30 years) with minimal maintenance (dust cleaning).  

   Oil-immersed: 20–25 years, but requires regular oil testing (for moisture/impurities) and replacement, increasing long term costs.  

Summary  

Dry-type transformers excel in safety, compactness, and indoor use, while Oil-immersed:transformers are preferred for high voltage, large capacity, and outdoor applications due to their superior insulation and cost-effectiveness at scale. The choice depends on voltage, environment, safety needs, and budget.