> Why are transformer ratings always given in VA and not in Watt?

ans: the t\f occurs in iron and core losses this losses iron losses depends on voltage and core losses depends upon current so transformer rating taken by VA but not in Watt

 

I've a transformer having following Rating.

Input: 220V
Output: 12V
Rating: 500VA
Load(at Transformer output): Heater (300Watt)

I need to calculate what exactly the Amp (or Power) at the Transformer input. this I need to select an appropriate UPS for supplying power to the transformer.

 

transformers are rated in VA because they undergo only two losses, 1.iron loss and 2. copper loss. the iron and copper losses are found out by the open circuit test and the closed circuit test respectively. as open circuit is carried out at rated voltage and short circuit test is carried out at rated current the losses are supposed to occur only due to voltage or current and not because of the power factor and therefore the rating of a transformer is in VA

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The transformer having winding, that means it having inductor and its property inductance always having lagging power factor. then how we can say transformer independent of power factor?

the motor also having the same kind of losses like transformer, then why it in KW?

i am really confused about those things. please help me to get clear.

 

In the case of the motor, the KW (or Hp) rating is because they're rated by the OUTPUT at the shaft, which is actual power, which is measured in watts rather than VA.