The transformer radiator is a passive heat exchanger made of multiple steel fins or tubes that provide a large surface area for hot oil to cool. Cooling fans are active devices mounted onto these radiators to force air across the fins, significantly accelerating the cooling process. Together, they allow the transformer to handle much higher electrical loads than it could with natural airflow alone.
Effective thermal management is the "lifeline" of a transformer, as excessive heat is the primary cause of insulation aging and failure. [
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- Transformer Radiator (Passive Cooling)
- Thermosiphon Effect: As transformer oil heats up, it becomes less dense and rises to the top of the main tank. It flows into the top header of the radiator, travels down through the narrow fins, and as it cools, it becomes denser and sinks back into the bottom of the main tank.
- Construction: Radiators consist of parallel panels or tubes typically made of durable steel or aluminum. They are often attached via butterfly valves, allowing individual radiator banks to be removed for maintenance without draining the entire transformer's oil.
- Cooling Fans (Active Cooling)
- Boosting Capacity: Adding fans converts a transformer from ONAN (Oil Natural Air Natural) to ONAF (Oil Natural Air Forced). This simple addition can increase a transformer's power rating by 25% to 33%.
- Automatic Control: Fans are rarely on all the time. They are typically controlled by a Winding Temperature Indicator (WTI) or thermostatic sensors that trigger the fans only when the oil reaches a specific temperature (e.g., 60°C to 70°C).
- Mounting: Fans are usually axial-flow types mounted on the side or bottom of the radiator bank to blow air directly across the cooling fins.
- Cooling Classes (Standard Codes):
- ONAN: Natural oil flow, natural air flow. Quiet and maintenance-free.
- ONAF: Natural oil flow, forced air flow (fans). Used for medium-to-large units under peak load.
- OFAF: Forced oil (pumps) and forced air (fans). Required for very high-capacity transmission transformers.
