in transformer core loss depends on voltage n cu loss
depends on current and power factor has no influence..
so we express in kva rating
in case of motor rotational loss, loss due to friction
windage loss etc are present. we cant express these losses
Basically, transformer losses always depending the rated
voltages & rated current. Because the core losses
calculated by open circuit method with full rated voltages
& the copper losses calculating by short circuit method
with full rated current.The losses of transformer is
depending the voltages(V) & current(A).Hence, we saying the
transformer capacity in KVA. The above not in motor
I think that motor is designed for any defined power o/p &
its load Pf is also known for that power thus we can give
its rating in kW. But in case of Xmer & alternator the load
is not fixed & so as the load PF thus its rating is given
I think In transformer & in generator the PF will be vary
depending up on the load connected with it, in motor it is
a inductive load & we can guess its PF, Usually for
inductive load PF will be 0.8 lagging.
transformer core lose find by using apply only rated voltage
and copper lossees find out by applying full load current,so
we obtaian exact performance in case motor added a
rotational losees so that it will measuredin kw.tranformer
measured in kva it is fixed .negligible p.f
Simplest and Guaranteed answer is :
KW and KVA are Active power and apparent power resp.
where Active power(W) needs Power factor known
and apparent power is without power factor.
The Motor's power factor is known so it can be written in
Active Power rating
where in case of generator, there are several connected
loads having different power factor, so we can't calculate
the mean power factor of connected loads hence its rating is
without power factor ; that is VA (volts x amp)
Can a 50-Hz designed transformer be used at 60-Hz system?
Is the same remains true, when a 60-Hz designed transformer
be used at 50-Hz system? Consider only frequency variation.
The voltage remains as rated value in all cases.
Justify the answer.