Answer / javed ahmad

we know that kw/kva=power factor. in case of transfomer we
do not know load on the transformer. and power factor comes
uder the load condition.from the given equation it is also
clear that kw=kva*power factor.so we can calculate kw
without power factor which comes under load condition.
So transformer are rated in kva .

Answer / kirti

kVA is the unit for apparent power. Apparent power consists
of active and reactive power. Active power is the share of
the apparent power which transmits energy from the source
(generator) to the user. Reactive power is the share of the
apparent power which represents a useless oscillation of
energy from the source to the user and back again.

It occurs when on account of some inertia in the system
there is a phase shift between voltage and current. This
means that the current does not change polarity synchronous
with the voltage. But the heat generated in a winding as
well as the eddy current losses generated in a transformer
core depend on the current only regardless of whether it
aligns with the voltage or not.

Therefore the heat is always proportional to the square of
the current amplitude irrespective of the phase angle (the
shift between voltage and current). So a transformer has to
be rated (and selected) by apparent power.

Answer / dinesh kumar mishra

'Cu' loss of a transformer depends on current and Iron loss
of a transformer depends on voltage. Hence total transformer
losses are depends upon voltage & current and it is
independent of power factor.So, transformers are rated in
KVA not in K.W.

Answer / ram

simply, transformer is not itself aload. it only step ups
or steps down the voltage without changing the supply
frequency, the power factor depends upon the load supplied
by the transformer.

Answer / dhaval

as core loss depend on applied voltage and copper loss
depend upon the applied current so the transformer is
rating in kva not in kw

Answer / parminder singh

bcz. core losses and cu losses are depend upon voltage and
current. so t/f rating in voltage-ampear. not in watt.

Answer / sandeep4653

maximum v and i fixed
so product vi so rating in kva

Answer / jenamanibehera

the core loss depends upon only voltage and current.so according to voltage and currents unit the ratings of trfr is made.therefore the ratings of trfr is in kva nt in wt.

Answer / don

because it is apperant power sharing of active and reactive
power.

Answer / ansar javaid

because the transformer is pure elecrical device that's why
we rated transformer in kva on the other side generator and
motor are electromechanical devices so we rated these
devices in kw and kva

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