Assuming you are describing a 7.5 MVA 55C base rated transformer with a 65C FA rating of 10.5 MVA, the overcurrent protection can handle the load and the ambient conditions do not result in temperatures above the design values (<30C ambient) I'd say yes 9 MVA at 100% L.F. is at the upper limit for the transformer.
APOWERENGR is correct in his analysis and conclusions, I would only caution that if the forced air is from a mechanical unit, extreme care should be taken with regards to the reliability and servicing of this unit. There must be strict coordination between your system loading and scheduled and un-scheduled "downtime" for the cooling unit. Some contingency plan should be in place for either load shedding or some such scheme when the cooling is off-line.
I used to work in xfmr repair shop and we always sold fan package KVA upgrades. The fan package gets its voltage derived from the transformer so that their is no worry about shutting down the xfmr due to to a mishap about ventalation. Of course all fan package does is make the oil if a wet xfmr recirculate more in the xfmr.
I know that the fan packages had a certain rating for kva heat disappation, so its a no brainer on figuring this out.
There are a number of assumptions and errors in your post:
"The fan package gets its voltage derived from the transformer so that their is no worry about shutting down the xfmr due to to a mishap about ventalation."
Nonsense. Fans fail. Auxiliary supplies fail. Either of these situations would cause very real problems with the transformer if it were loaded beyond its ONAN rating. Most owners would consider this cause for worry.
"Of course all fan package does is make the oil if a wet xfmr recirculate more in the xfmr."
Nonsense. The oil circulates by convection. The fan improves heat rejection from the oil by providing increased cooling to the surface of a finned radiator. If you want to increase oil circulation, fit a pump and convert the transformer to a forced oil (OFAF) or directed oil (ODAF) design. This will bring a significant increase in rating. It is not a trivial task.
