why transformer rated in KVA not in KW ? we know that W= v*i
Answer Posted / kingshuk dey
This is one of the sure questions of graduate interviews. I'll try to explain it in the simplest possible manner , using least technical words and more "English". :D
KVA is the power available for use. KW is the power that is actually used. Transformer is a source of power and supplies to the motor (consumer of power).
KW=KVA *cos(phi).
This "cos (phi)" or power factor is the efficiency in which the electrical system is utilizing power. cos (phi) is 0.85, means the system is 85% efficient. The rest 15% power is being wasted as heat etc. This factor only comes to play when there is a complete system (producing power and consuming power).
Hence transformer is rated as KVA and motor KW (cos phi comes into play in KW to specify it's efficiency to use the KVA power generated).
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