Answer / vasudeva rao

1) genarally transformers are operated under electrical
loads but induction machine works with mechanical loads.
2) so at the time of manfacturing manfacturer doesn't know
about the load power factor. i.e he doesn't know whether
consumer operates which type of power factor. that is why
transformer is in KVA induction machine is in KW


3) one more reason all of u knows copper loses depends upon
current and iron losses depends on voltage that is why in
KVA

Answer / dhiren

In alternator the power depends upon the operating load
which is don’t know to the designer. So it is rated in kva,
its power varies depending upon load. But in motor the
operating p.f is known(i.e.8lag) so it is rated in kw.

Answer / ibrahim

alternator generates reactive power which depends on type of
load so we cant able to say it is operating in a particular
p.f so it is in kva

Answer / its me nd

Alternator have to supply both Reactive as well as actve
power.the amount of active and reactive power is depends
upon load which is nt fixed/constant.so the alternator
rated in kva.
Now in case of induction motor it required to get the power
from the source to perform the work and to perform any work
only active power is required so it is rated in KW

Answer / nitin barnawal

alternater losses i.e core & copper losses depends upon voltage & current respectively but induction motor gives us real output i.e mechanical output which is a true power & represented in kilowatts.

Answer / jeetha sree

The alternator or the transformer consists 2 losses copper and the iron loss here the copper loss depends upon current and the iron loss depends upon the voltage hence alternator is rated in kva and not in kw.
here the motor have the fixed power factor i.e, the motor converts the active power in to mechanical power and we will not consider any losses hence the active power is rated watts hence the motor is rated in kw and not in kva...

Answer / sushanta

the rating of the alternator should be either KVA WITH P.f
OR KW such that we can select the rating of the prime mover
so that the active power should we known.

Answer / osho katyal

basically we have p=v i cos(phi) The alternator
losses-copper losses depend on voltage and core losses on
current and theres no dependence on power factor.
But in case of motors,the motor is connected to load and
thus power factor comes into role.

Answer / ibrahim

We generate reactive power (within a limit) with help of
changing excitation
for example .8 pf alternator is possible to operate at unity
by changing excitation .8 is the limit to generate reactive
power.if below .8 then we reduce real power only to generate
more reactive power.
But in motor full load it operates at .8 p.f only.......

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