what does 60/80/110 MVA TR. stands for?

[raynh]

Can any body explain what does it mean 60/80/110 MVA? for step up Power Transformers (60/80/110 MVA) 115/34.5kv,

regards

 

[asekhar]

Must be ratings with different means of cooling... minimum with ONAN, middle with ONAF, & highest with OFAF.
ONAN - Oil Natural Air Natural
ONAF - Oil Natural Air Forced
OFAF - Oil Forced Air Forced

Anand Sekhar

 

[tem1234]

Most of the transformer i saw was ONAN/ONAF/ONAF

The second ONAF come with a second stage of fan on the transformer so it can deliver more power since it's cool down by 2 stage of fan

 

[jghrist]

In ANSI land, you may also see it designated OA/FA/FA or OA/FA/FOA

 

[raynh]

Thanks every body, the cooling system was ONAN/ONAF/ONAF, and what confused me is that (the cooling system for the 80 &100 MVA is still the same using(ONAF), so how can the capacity of the transformer increases from 80 MVA to 110 MVA with the same cooling system, however what asekhar said makes sense as we can increase the capacity of TR by changing to OFAF

Any further remarks please

 

[asekhar]

raynh

tem1234 has already responded on your query.. the second stage ONAF switches on more fans to provide still higher cooling.

Anand Sekhar

 

[Gianoli]

You may also have different ratings with the same cooling method by allowing a high temperature rise. Example, 80MVA with a 55C rise, ??? MVA with a 65C rise.

 

[cuky2000]

Hi Jghrits,

Even thought still is common in the US to call the trasformer cooling designation as OA/FA/FA, the ANSI standard was revised a few years ago to make them more consistent with IEC designation. So the IEEE Std C57.12.00-2000 replaced the cooling designation OA/FA/FA by ONAN/ONAF/ONAF.

 

[dpc]

Some transformers have two stages of cooling fans. Middle rating is for one stage of fans running, highest rating is for both stages running. This is only possible for larger transformers with large surface area in the radiators.