Answer / r

the losses depends purely on voltage and current . that is
core loss is proportional to voltage and cu loss is
proportional to current, thats why the tr is rated in KVA
not in KW

Answer / s s nanal

Transformer is AC Static Inductive M/c where there are no
moving parts.Hence frictional losses are nil.In AC M/cs
power factor i.e.cosine of angle between voltage & current
is important.The relation between KVA & KW is given by
following formula. KVA = KW /P.F. or KW = KVA X P.F. This
angle between Voltage & current decides actual power
available.Transformer being highly inductive m/c power
factor is never = 1.Hence actual KW available is always
less than KVA. Hence X'mers are rated in KVA.

Answer / ashok

because of there are two type of loses in transformer one is iron loss and second is copper lose.iron lose is proportional to the voltage and copper lose is depends upon current hence transformer losses is measured in KVA.

Answer / vivek

and yes , one more thing the output of a transformer has no
realtion to the power factor of the load , ie the active and
reactive loading of a transformer can be done in any range
as long as the combined active and reactive loading does not
exceed the max current limit . this will also give you the
answer to why motors are rated in KW , as the power output
of a motor is dependent on only the active power it consumes
.....

Answer / suneetha

in oder machines lik motors also core loss is prop to
voltage n cu loss is prop to current..but dey are rated in
kw nly...y s t so???

Answer / sathish.b

the losses depends purely on voltage and current . that is
core loss is proportional to voltage and cu loss is
proportional to current, thats why the tr is rated in KVA
not in KW

Answer / vivek

the limiting factor in transformer loading is voltage and
current , so , specifying a transformer in KVA with a given
primary and secondry voltage gives he maximum loading
current in both the sides. coupled with the transformer base
impedence , it also gives the regulation and losses at any
load .

Answer / engr. tariq

KW = KVA * PF

According to this formula since power factor depends on
load or load current( Apparent /Real power ) therefore we
can say that the rating of transformer is in KVA.

Answer / mijibar rohaman

kva=kw/p.f
as pf never more than unity,so it can be varied with the
angle between voltage and current.so kw alsom may be
varied.as a result tranformer is rated as kva.

Answer / hyderabad

yes

mostly the questions were from machines... d.c. machines, transformer, synchronous and induction all theory paper........ few from power system... but the level of paper was easy.....

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