Q2Electrical Machine Design
Question
Q.2. What are the various cooling methods used for oil type transformers?
Answer
Oil-type transformers use cooling methods including ONAN, ONAF, OFAF, and OFWF, representing increasing levels of forced circulation of oil and/or air/water for progressively higher cooling capacity.
The various cooling methods used for oil-type transformers, in order of increasing cooling capacity, are: ONAN (Oil Natural, Air Natural) — natural convection of oil within the tank and natural convection of air over the external radiators, used for smaller transformers; ONAF (Oil Natural, Air Forced) — natural oil circulation combined with fans blowing air over the radiators to enhance heat removal, used for medium-to-large transformers requiring higher output than ONAN alone permits; OFAF (Oil Forced, Air Forced) — oil is actively pumped through the cooling circuit combined with forced air cooling via fans, used for large transformers; and OFWF (Oil Forced, Water Forced) — oil is pumped through a heat exchanger cooled by circulating water, used for the largest transformers or those in locations where adequate air cooling is impractical, offering the highest cooling capacity of the standard methods.