Transformer rating and impedance

[Cerkit]

Hi,

I am looking a transformer which has different ratings based on it being naturally cooled VS forced cooling. The nameplate states the impedance of the unit based on the transformer naturally cooled MVA value. How do I treat this unit if I wanted to model it, will the impedance change if I were to consider the forced cooling MVA? I understand converting impedances between different MVA bases, but I'm guessing in this instance whether the transformer is operating at the naturally or forced cooling MVA capacity the impedance will be the same yes?

Thanks

 

[Nayeem1993]

Actual impedance will be unchanged, but percentage(per unit) impedance will change as the base MVA has been changed.
By the way, In any power system modelling you need to specify the base MVA and base voltage of any unit(generator, transformer, motor etc) so it doesn't really matter which base you consider. The software will convert the data into a single base model and carry out the analysis accordingly.

 

[waross]

Actual impedance will be unchanged, but percentage(per unit) impedance will change as the base MVA has been changed.

Agree completely.