Transformer ratings

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mshields

mshields

Senior Member
Location
Boston, MA
For 15kV to 480V AND for
15kV to 4160V

On dry type transformers we've got the following ratings available.

OA/FA where OA = Open Air and FA = Fan Cooled. The difference is 33.3 percent capacity. But how's it work when you add 55/65 deg ratings correct?

What do you get e.g. OA/FA/??

For liquid types, what's the increase with fans? Is it still 33%? And again what different ratings are available if you combine temp rating with fan ratings?

Thanks,
 
zog

zog

Senior Member
Location
Charlotte, NC
Ok, a dry type would nopt have a OA rating, thats for a oil filled transformer, a dry type may be AA/FA with fans and would have 2 KVA ratings, the higher of the 2 is with the fan operational.

If you have 2 temp rise ratings like 55/65, you would also have 2 KVA ratings, the higher is for a set period of time at 65C rise.

Liquid filled may be OA/FA/FOA, natural circulation/fans operational/forced flow and have 3 KVA ratings.

AS far as I know, there is not a set % for increase in KVA, it is a rating from the manufacturer.

Why are you asking this question? Just to learn, or for some application?
 
kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
The increase on a 55/65 deg C transformer is approximately 13% for planning purposes. The increase in rating is continuous. Basically, you get more MVA just by allowing the temperature to rise 10 degrees to 65 Deg C above a 40 Deg C ambient.

Dry Types and oil filled transformers have different classes, such as AA, FA, ONAN, ONAF, etc. Oil filled transformer prior to, I believe 2002, have the old class designation of OA, FA, FOA, etc. IEEE stds changed to be more consistent with IEC (international stds). Refer to IEEE C57 standards for a full description of the various types.

As far as by adding fans, it can vary from a 25% increase or 33% increase depending on the size, cooling medium, type, etc. Again refer to IEEE C57 standards.

An example: Dry Type transformer, 15-4.16kV, 2.0/2.5 MVA, AA/FA, 2.26/2.82 MVA, 55/65 deg C.
 
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