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I have recently run across large transformer cooling ratings I am not familiar with and cannot find in several engineering reference books.

Typically a rating may have several MVA/MVA/MVA number size ratings followed by cooling rating of OA/FA/FOA (Oil-Air/Forced Air [fans]/Forced Oil-Air [fans & pumps].

Does anyone know the meaning of ONAN/ONAF/ONAF?

ONAN-OIL NATURAL AIR NATURAL
ONAF-OIL NATURAL AIR FORCE
OFAF-OIL FORCE AIR FORCE

N = natural (or thermosyphon) circulation - hot oil rises to the top of the tank, passes to the cooling fins and is cooled so increases in density and sinks through the fins back to the bottom of the tank.

F = forced - using a pump (for oil) or fan (for air).

So ONAN is a mode of operation with oil circulating by thermosyphon effects, air also passing through the cooling fins by natural convection.

ONAF uses thermosyphon circulation of the oil with a fan to increase the air flow and therefore increase the rating.

OFAN would use a pump to circulate oil but again use natural convection for the air.

AFAF would use a pump to circulate the oil and fans to drive air over the cooling fins.

HTH,
Bruce

Dear T. Cunningham,

ONAN = Oil Natural Air Natural, without pumps and fans
ONAF = Oil Natural Air Forced, without pumps for oil, with fans for air
OFAF = Oil Forced Air Forced, with pump for oil and fans for air

Regards,
bambangfx

Responding to T. Cunningham's query:

o ONAN means Oil Natural (thermal syphon action) circulation with Air Naturally circulated for cooling.

o ONAF means Oil Natural Air Forced (fan) cooling.

o OFAF means Oil Forced (pumped) circulation and Air Forced (fan) cooling.

o OFW means Oil Forced (pumped) and the oil is cooled with Water.

Let me know if you need an example of how the rating is used!

Regards, Phil Corso, PE (cepsicon@aol.com)

Hi there Mr. T Cunningham

ONAN = Oil Natural, Air Natural - no fans or pumps running, natural convection through radiators

ONAF = Oil Natural, Air Forced - no oil pump running, fans running forcing air across radiators

OFAF = Oil forced (pumped), Air Forced (Fans)

Cheers
John R Williams

Sir,

I would like to know how to design a transformer radiator. I have searched the internet but I didn't find one. Could you please help me out? i.e. lz tell me if there is any book for radiator design, or any site that provides support for it.

Thanks.

Ritesh Agrawal

> ONAN-OIL NATURAL AIR NATURAL
> ONAF-OIL NATURAL AIR FORCE
> OFAF-OIL FORCE AIR FORCE

How about OFP type, any ideas?

ONAN: Oil natural Air natural
ONAF: Oil natural Air forced

These abbreviations denote the cooling methods used for transformers. The type of cooling used for a particular transformer depends upon its MVA rating. Smaller rating transformers (less than 100MVA) are generally ONAN type.