Rating of Transformers: KVA vs KW

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SUMMARY

The rating of transformers is expressed in KVA (kilovolt-amperes) rather than KW (kilowatts) because KVA measures apparent power, while KW measures real power. The relationship between these two is defined by the formula: real power = power factor × apparent power. Since loads connected to transformers can have reactance, resulting in a power factor of less than 1, the total power consumed is represented as apparent power in VA. Therefore, transformers are rated in KVA to account for these variations in load characteristics.

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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
 
Last edited:
thanx for help.
 

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