Answer / vijay shinde

transformer rating is in kva because iron losses are
depends on voltage of transformer and copper losses are
depends on current of transformer so its in kva

Answer / praveen420

rated transformer o/p is limited by heating and hence by the losses in transformer.mainly two type of losses occur in transformer iron loss and copper loss.iron loss depend on voltage and cu loss on current(amp)and these are almost unaffected by load pf so rating of transformer expp.in kva,va rather than kw.
w=v*i*cos(angle) in case of AC.
w=v*i in case of DC

Answer / kingshuk dey

This is one of the sure questions of graduate interviews. I'll try to explain it in the simplest possible manner , using least technical words and more "English". :D

KVA is the power available for use. KW is the power that is actually used. Transformer is a source of power and supplies to the motor (consumer of power).
KW=KVA *cos(phi).
This "cos (phi)" or power factor is the efficiency in which the electrical system is utilizing power. cos (phi) is 0.85, means the system is 85% efficient. The rest 15% power is being wasted as heat etc. This factor only comes to play when there is a complete system (producing power and consuming power).
Hence transformer is rated as KVA and motor KW (cos phi comes into play in KW to specify it's efficiency to use the KVA power generated).

Answer / lalgpt

Transformer rating is always on KVA that is
Kilo Volt Ampere Simply Volt ampere

but equation of power is VICos()

And the transformer has two losses one is copper loss
and the other is the core loss these two losses
are depending on current (I) and Voltage(V) only not
on Cos() that is why rating is in VA

Answer / pratheesh

Transformer is a power source(supplier) whicah can
deliver X amperes at rated voltage. So units of these
values are Voltag(V) and Current(I). It means all the
power delivering equipmets such as Transformers and
Generators are supplying I ampere at V voltage. Thats y
its rating is V*I == V*A

Power W= V*I cosQ.
Not V*I. (It is in DC)

Answer / guru

Transformer is mere equipment which transforms the voltage
and current as per the requirement. KW are rated for
equipments which converts electrical energy to other energy.

Transformer rating in KVA is due to it converts electrical
energy to electrical energy and all electrical ratings are
done only in voltage and current or combination of both,
like CB rating in Voltage and current, Bus bar rating in
amperes etc.

IN SINGLE PH TRANSFORMER IF LEKAGE IMPEDANCE DROP IS NEGLECTED ,THE FLUX IN THE MAGNETIC CORE and the lekage flux linking a winding are a)proportional to the applied v to the winding i respectively.

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