why transformer ratings in kva?

Answer Posted / pradyumna chandra panda

Power given to the transformer is Apparent power (K)
it is the supply power of the power house and the power
given by the transformer to the Load is the true power or
Active power which is actual used by the load and rest is
the reactive power i.e. square of apparent power including
iron loss & copper loss in KVA = square of true power in KW
+ square of reactive power in KVAR. A sound transformer
efficiency is 98% (input power- Iron loss (k) & copper loss
= output power).
For full resistive load (at unity pf ) a 100 KVA transformer
gives 100 KW (approx.) true power, and for inductive power
at .8 pf the same will able to give 80 KW (approx.) true
power, but the types of load (its pf) is not know before
which to be connected across the transformer, this is only
why the transformers are rated in KVA and it is meaningless
to discuss about the iron loss and copper loss because the
Inventor and UPS are also rated in KVA.


In other hand or in simply we can say due to unknowing power
factor the transformer, generator etc are rated in KVA. In
heavy size transformer copper loss is more and it vary with
load and Clemet i.e. transformer oil condition but it is not
main reason to rating the transformer in KVA.


Pradyumna Chandra Panda
Berhampur Mob 9861357949

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