Answer / chin2

power losses depends on current (copper) and voltage (iron)
so if we take power KW it is also a factor of power factor
so we use KVA

Answer / tanu singh

rating of any machine is depend to the losses in that m/c.
in x-mer, the iron losses and hystersis losses dependent to
the voltage. and copper losses depend to the current. it's
the only reason to take the ratings in kva.

Answer / saurabh bhardwaj

transformer output is always depends upon the power factor,
P=V*I*p.f, T/F has not work as a load on it when there is no
load there is no p.f. so it's rating in KVA.KVA RATING IS
GIVEN BY MANUFACTURER WHO HASN'T KNOW WHAT TYPE OF LOAD WILL
APPLY IN FUTURE BY CONSUMER.

Answer / aditi

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 / praful nandankar

As we know that copper losses depend upon square of current
and core losses depend upon voltage applied.
Apparent power is the vector sum of reactive power and
active power. active power is the useful energy transferred
from primary ckt to secondary ckt. Reactive power is used
to create magnetic flux in the core. Hence we hav to take
into account the active as well as reactive power.Hence the
rating of transformer is alwAys in KVA.

Answer / aruna

transformer rating is mainly depends on core losses.those
losses depends on temp which can be depends on current
rating.. no need of power factor cal..

Answer / parth patel

when we install any new transformer we have only load
current as known quantity accordingly the secondary voltage
is selected. but we dont know which type of load will be
connected on the secondary side it may be inductive ,
capacitive , resistive or combination of them.So as we dont
know about the load we dont know power factor of the load
thats why the ratings of transformer is in kva and not in
kw.

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