Answer / rohan

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.Thus power depends on product of current
and voltage only and not on product of current voltage and
phase angle.

Answer / john mohd

Transformers are rated in kva's because at the time of manufacture the power factor (cos phi)of the machine is not known I.e at the time of desighning you do not know which type of load is placed on that I.e the power factor is unknown

Answer / ankaraju.k

The losses in trasformer only depends on voltage under no
load condition and curret under load condition,so it is
independent on power factor on which it is operating load

Answer / vimal raj

transormer is mainly depend on the current an voltage .were
the core an copper losses are due to voltage an current an
this is independent to power factor so power factor is not
alter due this losses for this reason transformer rated in
kva..........

Answer / fred gleicher

KW, or kilowatt, assumes both current and voltage are in
phase. In a transformer, it is possible for current and
voltage to be out of phase ( since a transformer is
inherently normally an inductive device ). Therefore, the
rating is given in VA or volt amps, instead of watts,
showing that current and voltage may be out of phase. The K
comes from the MKS system and is an abbreviation for
thousand. It just makes it easier to write the power rating
of the device, most transformers ordinary folks see are
rated in the VA range, but electrical linemen see devices
rated in the KVA range every day.

Answer / vicky

voltage unit is volts and current unit is amps then high
voltage for transformer that called kva

Answer / prasad

In all A.C. machines (which includes motors whose rating
are in KW )iron losses are proportional to voltage & copper
losses are proportional to current.
The machine rating is given in terms of its output. The
transformer output is electrical energy & thus its rating
is same as energy i.e. KVA.
Same is the case with generator

Answer / tarun

Because Transformer does not depend on PF it depends on
the max. current. but motor depends upon the PF and work
acc. to their PF. thats why it denoted in KW while
Generator denoted in KVAQ.

Answer / bhavesh

adding to above answer Transformer is not a load and having
no effect on P.F and it only transfer the constant power
from one voltage level to another voltrage level without
changing frequency thats why transformer are rated in KVA
or MVA

how can we determine size of a cable by knowing the kw or current rating of a load?how can we calculate the resistance box of a slip ring motor?

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