Why the transformer ratings is given in "KVA" rather than in KW?

Because even transformer has its power factor.

Simply speaking, Power (say, from LV to HV) is transferred purely on the basis of No. of Turns on LV and on HV. Power Factor which depends on the nature of load, has no effect on the Turn Ratio - on transformation of Power.

There are two types of losses within a transformer, copper losses and iron losses. Copper losses depend on current which passes through the transformer winding while iron losses
(core losses) depends on the voltage. That's the reason why the rating is in kVA and not in kW.

Because it's the product of rated voltage (V) and rated current (A), irrespective of power factor, or power transformed, or losses.

Simply because the load applied to a transformer is in terms of KVA. Now, understand that is comprised of KW and KVAR, where KW is the real component and KVAR is the reactive component. The result of the combination of KW and KVAR is KVA, the actual loading on the transformer. Review power triangle and power factor.

Also understand that capacitors can be applied at the transformer secondary to improve the power factor and thus unload the transformer. This is because capacitive reactance is 180 degrees out of phase with inductive reactance. Thus the magnitude of the KVAR component becomes smaller and KVA becomes close to KW. This is all about vector analysis..

Hope this helps.

in fact, you face with two kinds of limits, first, voltage limits, which is mostly depended on the type of dielectrics and isolation. and the second one is about current, and related to the type and diameter of conductors and the standard working temperature of the transformer. By multiplication of these two ratings(rated voltage and rated current), you can obtain rating KVA of the transformer, and as you can see, it doesn't relate to load's power-factor.

Not only transformers, most loads are. KVA is the true power measure as it combines both the passive (KW) and reactive (KVAr) components of power consumption.

Transformers are rated in {VA, kVA, MVA etc.} due to flows of active and reactive power through transformer. In case of transformer we have active power losses as consequence of existence inside resistance of windings (primary and secondary) and existence of active power losses of ferromagnetic core and other side we have reactive power losses as consequence of existence losses of magnetic flux (primary and secondary) and existence of reactive power losses of ferromagnetic core... [VA]=sqrt(sqr[W]+sqr[VAr])