Answer / nithi

we can design the transformer for some rated voltage &
rated current ,power factor depends on the load.so,we
cannot predict the p.f. while designing the transformer.
But in the case of generator ,it has to supply real
power (depends on the capacity of the prime mover)& some
amount of reactive power to the system (depends on the
rating of exciter).that's why generators are supplied with
the name plate details including p.f.,kva rating & kw
rating.
in case of motor,it has to take some hp(kw) load
(real power) ,for that it uses some amount of power for
producing the magnetic field (magnetizing power--reactive
power).so,during the design itself we have idea about how
much of load the motor should take (hp load).This is the
reason why the motor is rated in kw,p.f..

Answer / lokesh

copper losses of a transformer depends on CURRENT and irons
of a transformer depends on VOLTAGE not an phase angle
between voltage and current. that is why transformer rating
in KVA not an KW.

Answer / sravani

we can design the transformer for some rated voltage &
rated current ,power factor depends on the load.so,we
cannot predict the p.f. while designing the transformer.
But in the case of generator ,it has to supply real
power (depends on the capacity of the prime mover)& some
amount of reactive power to the system (depends on the
rating of exciter).that's why generators are supplied with
the name plate details including p.f.,kva rating & kw
rating.
in case of motor,it has to take some hp(kw) load
(real power) ,for that it uses some amount of power for
producing the magnetic field (magnetizing power--reactive
power).so,during the design itself we have idea about how
much of load the motor should take (hp load).This is the
reason why the motor is rated in kw,p.f..

Answer / tapan k ghosh

The output expected from a generator or transformer is
electrical output. Electrical output contains both active
and reactive components and hence these equipment are rated
in terms of composite power,kVA i.e.sqrt(active2+reactive2).

Output expected from a motor is motive power i.e. active
one and hence motor is rated as kW.

Answer / iyswarya sithanathan

The convention is that source power is mentioned in KVA and load power to be mentioned in KW.

Answer / nilesh chavan

The rating of transformer is given in KVA instead of KW
because total transformer loss depends on VA.

Answer / rajneesh

Transformer has apparent type power while any machine has
the power of active type.

Answer / yogesh

Transformer and genrator PF depends on the nature of
connected load ( Motor ), But motor has its own fixed Power
factor

Therefore Transformer and genrator capacity shown in KVA (
Without PF ) and motor Capacity shows in Kw ( with power
factor )

Answer / j. nagarajan

Actually the question itself is wrong. The rating of
Generators are also mentioned in KVA as both tr. & gen have
a same function of producing apparent power which doesn't
have power factor.

The power factor is a measurement voltage & current utilised
and it will be ratio of apparant power to active power.

But the motors are mentioned in active power as they are
used in various industrial/domestic application utilising
the current & voltage with desired power factor.

Answer / mani_mc2006

iam not sure. but my answer is Transformer not having load
variation. but Generators and motors having load variation.
so power factor will not be constant. That's why mentioned
like this.

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