Answer / aslam ali

Transformers has two types of losses i.e. Load loss/copper loss & iron loss/no load loss.Load loss mainly depends on cureent(I)& no load loss depends on voltage.As a transformer never generate power,it only transfer VA or burden or load.So it's rating is always called in terms of VA.

Answer / guest

iron loss depends upon voltage and copper loss depends upon
the curent.so the product of those are the power.thats why the
transformers are rated in VA or KVA.

Answer / sunil kumar sinha

Transformer is an electrical device which transform power
from one voltage level to another voltage level. i.e
promary to seceondrt voltage level. It may be step up , may
be step down.
The transformer design is limited by two parameters : 1)
Voltage 2) current.

Voltage parameter decides the amount of insulation over the
coil/ windings to prevent interturn fault or earth fault of
transformer windings.Hence predetermined voltage level of
primary and secondary will decide the amount and nature of
winding insulation.
The second parameter is current which is responsible for
generating heat in the winding thus the transformer. If
transformer current is increased the heat loss will
increase and further heat transformer. The temperature of
transformer winding is controlled by cooling deviec of
transformer which is also predetermined and can restrict
winding temperature within its limit for a defined rise in
temperature. we all are well aware that rise in winding
temperature beyond given limit weekens the insulation and
results in failure of insulation, hence transformer.
due to above two reasons we must define the voltage level
and the current level of transformer. the product of these
two paramenter is VA or KVA, hence transformer is to be
rated with KVA.Power factor plays no role to limit the
transformer function, hence it is not rated in terme of
power.

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