Why transformer is rated in KVA?

If a 60 Hz transformer is operated in 50 Hz, but at rated voltage, will it be hotter or cooler at full load?

We know ,

If a transformer rated in KW, it will be meaning less. Because will change according to load. So transformer is rated in KVA. As seen, Cu loss of a transformer depends on current and iron loss on voltage. Hence total transformer loss depends on volt-amp (VA) and not on phase angle between voltage and current i.e. it is independent of load power factor. That is why rating transformer is in KVA not in KW.

If rated voltage is applied but a frequency other than rated is used in a transformer, it is seen from equation, , that the flux must change inversely with the frequency change in order to maintain the same induced voltage. The core loss varies almost directly as the square of the flux and only directly with the frequency. A decrease in the supply Frequency will therefore require an increase in flux and consequently an increase in the core loss. Moreover, an increased mutual flux requires an increased magnetizing current , while the increased core loss requires an increased core loss component . Together, they combine to increase the no-load current, and therefore the primary current under load, Thus if a transformer rated at 60 Hz is operated on a 50 Hz supply line, overheating will occur if it carries rated KVA at rated voltage.