Views: 0 Author: Site Editor Publish Time: 2026-01-22 Origin: Site
The main difference between ONAF and OFAF cooling lies in how the transformer oil is circulated.
ONAF (Oil Natural Air Forced):
Oil circulates naturally inside the transformer and cooler due to temperature-driven convection. Only the airflow is forced by fans.
OFAF (Oil Forced Air Forced):
Oil circulation is forced by pumps, and airflow is also forced by fans. Both heat transfer media are mechanically driven.
| Aspect | ONAF Cooling | OFAF Cooling |
|---|---|---|
| Oil circulation | Natural convection | Pump-forced circulation |
| Air circulation | Forced by fans | Forced by fans |
| Oil flow control | Limited | Precise and controllable |
| Cooling capacity | Medium | High |
| Typical application | Medium-power transformers | Large or high-load transformers |
| System complexity | Lower | Higher |
| Maintenance demand | Lower | Higher (oil pumps + fans) |
| Overload capability | Moderate | High |
ONAF systems are simpler, more economical, and reliable where natural oil flow is sufficient.
OFAF systems provide significantly higher heat removal, allowing:
Higher transformer MVA ratings
Better temperature control under peak loads
More compact cooler designs
In short:
ONAF = natural oil flow + forced air
OFAF = forced oil flow + forced air
The choice depends on transformer size, load profile, ambient conditions, and required cooling performance.
