Transformer nameplate

[ernric43]

I'm trying to figure out how to interpret a nameplate. Normally there pretty straight forward but even my Siemens rep isn't quite sure.
The transformer is a 13,200 primary, 480/240 secondary. We have the transformer connected for 480 secondary. It has a 55-65C rise. The kva rating, which is in question, reads 2500-2800/3333-3733.
Typically a 2,500 kva transformer rating goes up 30% with fans i.e. 3333. I don't understand how the 2800/3733 applies?

 

[david luchini]

I'm trying to figure out how to interpret a nameplate. Normally there pretty straight forward but even my Siemens rep isn't quite sure.
The transformer is a 13,200 primary, 480/240 secondary. We have the transformer connected for 480 secondary. It has a 55-65C rise. The kva rating, which is in question, reads 2500-2800/3333-3733.
Typically a 2,500 kva transformer rating goes up 30% with fans i.e. 3333. I don't understand how the 2800/3733 applies?

Just a guess, but I would think 2500 is the rating with a 55C rise, and 2800 is the rating with a 65C rise.

 

[kingpb]

A 55/65 deg C rise gives you an additional 12-13% increase, this is typical.

The 3333/3733 rating is due to a single stage of fans.

Typically for sizes less than 2500KVA the increase is 15%, 25% for sizes greater than 2500KVA and less than 10MVA,
and anything over 10MVA is 33% increase.

Of course, those are only guidelines, you can always specify something else, within reason.

You might also see it written as 2500/3333-3733 KVA, ONAN/ONAF, 55/65 deg C

No offense intended; but if the rep didn't understand that, I would suggest finding one more knowledgeable about transformers. This is pretty basic stuff for someone that is familiar with transformers.