Transformer RatingPublished on 24/2/2012 & updated on Saturday 10th of March 2018 at 10:56:15 PM
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In a transformer, losses are of two types
- Constant losses or core losses - These depend on V
- Variable losses or ohmic (I2R) losses - These depend on I
Lets us take an example, a transformer working on rated voltage and rated current with load power factor equal to zero, as load power factor is zero it will deliver zero power to load, but it has rated KVA output, hence rating must be expressed in KVA.
For any transformer rated input in KVA at the primary = rated output in KVA at secondary + losses.
As transformer runs on very high efficiency its losses can be neglected and hence rated input in KVA at the primary = rated output in KVA at secondary. From here we can say that rated KVA marked on the nameplate of transformer refers to both the windings. i.e KVA rating for both the primary and secondary winding is same.
The KVA rating mentioned on the nameplate of the transformer is load side KVA but only at full load condition.
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