Transformer

Out of my league here and just a guess. How about 10 MVA with a max of 12.5 MVA

or 10 MVA on the low power side and 12.5 on the high power side?

What is SLD?

Single line diagram

How about Dyn11?

The Vector group 'dyn11' means your transformer is a delta to star (with neutral) transformation , lagging at 30 degrees

OK ta

Usually transformers with dual (or more) ratings have additional cooling available (fans or oil pumps on radiators), so that the first number 10MVA is for self-cooled (convective cooling). The second rating 12.5MVA is for when the fans are turned on, so that the radiators can remove more heat from the oil.

The other possibility is that both are for self-cooled, but the first # is for 55°C temperature rise and the second is for 65°C rise. You can easily tell by looking at the unit and its nameplate. If there are fans on the radiators, it is the first of the options I described.

As for Dyn11, do a little searching on "transformer vector groups." It has been discussed in this forum previously, and there are sites that explain it simply.

PeterT has correctly decribed it. The transformer, for most part of its operation will be used at 8 MVA only.
Only one thing i would like to add. When ordering for this transformer, pls ensure that the vendor shall design the windings suitable to operate for 10 MVA.
This point usually goes missing in specifications.
Current density and Losses(no-load and full load) at both ratings shall be collected from vendor.

Dear Mr. Sprabakar22,

The 10/12.5 MVA can be explained in simple term - " BY INCREASING THE COOLING EFFECT/ASPECT of the TRANSFORMER, THE SAME TRANSFORMER CAN BE LOADED TO 12.5 MVA from 10 MVA, BY LIMITING THE TEMPERATURE RISE of the TRANSFORMER WINDING.

The cooling effect is increased by either switching on the fans, as explained by other CR4 Member, or provide ADDITIONAL COOLING AREA for dissipation of Heat - so as to limit the Temp.Rise in the windings to the same limit when load is increased to 12.5 MVA.

Thanks,

DHAYANANDHAN.S

it simply means that your transformer is rated at 10MVA under natural cooling methods and can be loaded upto 12.5MVA on forced cooling methods.

11/3.34KV is the voltage transformation. i.e 11KV to 3.34KV

Dyn is the vector group. D for Delta. 'y' for star. 'n' for neutral. meaning it is a Delta to star(with neutral on the star side) transformer.