What Are The Common Cooling Methods for Oil-immersed Transformers?

What are the common cooling methods for oil-immersed transformers?

Oil-immersed natural cooling (ONAN)

Principle: Relies entirely on natural forces for heat dissipation. After absorbing heat, transformer oil naturally rises, transferring heat to the air through the tank walls and radiators. Natural convection then carries the heat away.

Suitable Scenarios: Smaller capacity transformers (typically ≤3150kVA), such as distribution transformers and small industrial transformers. Requires good ventilation in the installation environment.

Oil-immersed forced air-cooled (OFAF)

Principle: Fans are installed on the tank or radiators to accelerate heat dissipation through forced airflow. Oil circulation remains natural convection, but enhances heat exchange efficiency on the air side.

Suitable for: Medium-capacity transformers (3150kVA-63000kVA), such as main transformers in small-to-medium substations, requiring enhanced cooling beyond natural dissipation.

Forced Oil Circulation Air-Cooled (ODAF)

Principle: An oil pump forces transformer oil to circulate between the tank and radiators, accelerating heat transfer; air-side heat transfer remains natural convection.

Applicable Scenarios: Large-capacity transformers (typically ≥63,000 kVA), such as industrial power transformers, requiring enhanced oil-side circulation to improve overall cooling efficiency.

Forced Oil Circulation with Air Cooling (ODWF)

Principle: Simultaneously employs oil pump-forced oil circulation and fan-forced airflow, maximizing heat exchange efficiency on both oil and air sides.

Applicable Scenarios: High-capacity, high-load transformers (e.g., 110kV and above power transformers) or units installed in harsh environments like high temperatures or elevations requiring maximum cooling capacity.

Key Factors for Cooling Method Selection

Transformer Capacity: Smaller capacities favor natural cooling (e.g., ONAN); larger capacities require forced cooling (e.g., ODWF).

Operating Load: Transformers operating at full load for extended periods require forced cooling methods with higher heat exchange efficiency.

Environmental Conditions: High-temperature, high-humidity, or dusty environments prioritize forced air cooling (OFAF/ODWF) and necessitate enhanced equipment protection.