Rating of Transformers: KVA vs KW

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Transformers are rated in KVA (kilovolt-amperes) rather than KW (kilowatts) because KVA measures apparent power, which accounts for both real power and reactive power. The relationship between real power and apparent power is defined by the power factor, which can be less than one due to the load's reactance. This means that the actual power consumed may differ from the apparent power, making KVA a more accurate representation of a transformer's capacity. Using KVA ensures that the rating reflects the total power handling capability of the transformer without being affected by the power factor. Therefore, transformers are rated in KVA to provide a clearer understanding of their performance under varying load conditions.
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why is the Rating of Transformer is in KVA and not in KW?
 
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VA (volt-ampere) is the unit for apparent power. W(watt) is the unit for real power. The relation between the two is:

real power = power factor \cdot apparent power

The load that you may connect to a transformer could have a reactance which results in a power factor less then 1 for the load and so the total power consumed by the load would be it's apparent power (expressed in VA) and not it's real power (expressed in W). That's why the power rating of a transformer is given in VA and not in W.

Check this Wikipedia articles on:
AC power
Power factor
 
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thanx for help.
 

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