BECAUSE A TRANSFORMER HAS ELECTRIC ENERGY AT INPUT AND
OUTPUT SIDE WHEREAS A MOTOR HAS MECHANICAL ENERGY AT THE
OUTPUT. MECHANICAL ENERGY HAS THE UNIT OF WATTS.
transformer is nothing but power producing equipment.So the
powre p=V*I.v=Voltage,I=Amps.the minimum rating of the
distribution transformer is 1000V.i.e 1 Kilo
volt,v=volts,&I=amps.So thats while we can saying in KVA.
Moter rating in H.P & 1 H.P=0.732kiloWatts.
So moters having load is almost Drives.
In transformer there are tho typw of losses core losses and
copper losses. core losses depends upon voltage and copper
losses depend upon current. there is no windage losses in
transformer whereas in motor it occurs.
so, in conclusion there is no any factor in transformer
which relates with power factor so the rating of
transformer is in KVA instead of KW.
it is because a transformer uses ac voltage and therefore
the voltage and current are not always in phase whereas a
motor uses dc voltage to produce the turning effect(voltage
and current are always in-phase)
when we calculation the power of motor : p= v*i *cos&
but when ------------------------ trans : s= v*i = va
at trans total power maen that : s=p+q
wher: s = total power or apparent power
p= active power( this is the force depent in motion
motor )
q= reactive power( depend in sometime losses)
wehre cos&= real power/apparent
finaly all of above are unit of power
The copper loss of a transformer depends on current and iron
loss depends on voltage.Hence total losses depends on volt
ampere(VA) only and it is independent of load power
factor.That is why the rating of Transformer is given in KVA.
RATING is given in kw when we have any knowledge about the power factor of the load which is to be connected on the output side.
in case of the transformers we have no information about the power factor of the load so it is evident to define its ratings in terms of (VA)
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