Why Transformer Rating in KVA? and Why not in KW?

Why Transformer Rating in KVA? with examples:

1. Any transformer includes core losses and copper losses.
2. Core losses are based on input voltage. (Transformer is a Source)
3. Copper losses are based on current flowing through winding.
4. Therefore total loses are based on voltage in addition to current but not on power factor. Thus the rating of transformer is done in KVA not in KW.

One thing more : Because the output power of transformer are Active and reactive power.   KVA=KW+KVAR

Other Answers related to Transformer KVA rating:

(Transformer is a Source) Electrical Source is Usually rated in KVA. 

(Motor is a Load) Electrical Loads are usually rated in KW or Hp. 

Power Factor  when remained controlled {Around Unity}. Power in KVA to be utilized by the Loads remains equal to rated Power KW or HP rating of Loads.

When Power Factor Decreases, demand increases in KVA. As Voltages to remain same, Hence unwanted Current increases in the system & which may lead to unwanted Tripping or Burnouts in the systems.

So all Electrical Engineers & Technicians beware of Power factor of your Supervised Electrical Systems.

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