Answer / rutulsoni

there is two types of losses occured in transformer which are copper loss and iron loss.Copper loss is always  measured in ampere and hysteris loss measured in voltage so its rating comes in KVA. 

Answer / ep

Transformer rating comes in KVA not in KW, because - there are two types of transformer losses (Copper losses and Iron losses). Copper loss depends on current and Iron/Core/Insulation losses depends on voltage. Hence, total losses are dependent on amp-volt (VA), not on phase angle between current and voltage. It means losses are independent of load power factor (cos phi).
That's why transformer rating comes in KVA not in KW

Answer / kothandaraman

Because of transformer there is no lagging and leading current vector with reference to voltage vector. PF means the cosine value of the angle difference between voltage vector and current vector. If current vector lags the voltage vector, it is lagging, for example inductance type of loads, i.e motor. If current vector leads the voltage vector, it is leading, for example capacitance type of loads, i.e. capacitors and synchronous motors.

Answer / sagar

the transformer rating is in KVA because manufacturer dont know the Load Power factor thats why they specified it in KVA which is nearly Permanant losses

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