Answer / nithi

We can design the machines only for rated voltage(insulation
arrangement) & rated current(cooling arrangement,winding
thickness).
we can't predict the power factor while designing the
machine.Because,it is depending upon the load .

This is reason for why transformers & alternators
are rated in KVA.

Answer / iamdon

Rating of an alternator or any electrical machine/apparatus
reflects its load carrying capability without
overheating.Temperature rise (major threat to insulation)
arises due to internal loss within the machine.
These internal losses include
1)Copper loss and
2)Core or Fe loss(hysterisis and eddy)
Both losses are independent of power factor.

Copper loss is directly proportionl to I*I
Core loss is function of voltage applied/genetated.

Both loss must be taken into account for rating
purpose.Which is only possible with taking VA which has
nothing to do with power factor.

Author:arbelectbit@yahoo.com

Answer / shariff

Transformers or alternators are rated in kvA not in kw/MW
bcoz its losses like hystersis or eddy current or copper
losses are depend upon the frequency or current non of them
on the pf. There is no consideration of pf for this machines
hence they are rated in kvA's.

Answer / sohag kumar saha

Cu loss depends on current & iron loss depends on voltage.
Hence total Transformer/Alterntor loss depends on
volt-ampere(VA) and not on phase angle between voltage &
current i.e., it is independent of load power factor.That is
why, rating of transformers is in kVA & not in kW.

Answer / iamdon

Very well said by Nithi.

Answer / goud

the corelosses depend on voltage and copper losses dependon
current .so the rating of alternator or transformer are
mentioned in kva

Answer / nitin k

generally while designing an alternator we must consider 2 circuits:. i.e. electrical ckt.& magnetic ckt. Electrical ckt.is designed by considering current & magnetic circuit by volt. thats why rating is in kva.

Answer / padmaja.s.

in transformers and alternators we have 2 types or
losses..those are eddy current and hysterious losses.eddy
current losses are depends on current..trese are variable
losses.and hysterious losses depends on voltage.so these
two losses are depends on current and voltage...so the
ratings of transformer and alternaters are rated in
voltampers(VA)Or KVA

Answer / arijit

answer no 3 is perfect

Answer / oni

cu loss of transformer/alternator depends on current and iron loss on voltage.Hence total loss depends on volt-ampere(VA) and not phase angle between voltage and current that means it is independent of load power factor. That is why rating of transformer/ alternator is in KVA and not in KW.

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