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Why Transformer is rated in KVA?

 Why Transformer is rated in KVA?
 

Well there are different two reasons for this.

 

The first reason they normally use to explain for this is depending on the losses of the transformer.

Consider a single phase transformer supplying a power VICosØ to the load. The two losses that occur in transformer are copper loss and core or iron loss. This copper loss depends on the current flowing through the conductor and iron loss depends on the voltage and not on the phase angle between voltage and current(cosØ). That is the losses are independent to the power factor of the load.

Hence the total losses depends upon the volt-ampere(VA), the transformer is rated in VA or KVA or MVA.

 

The second reason is from the view point of manufacturer.

The manufacturer doesn’t know the power factor of the load or the type of load connected at the consumer end. Since the power handled by the transformer depends on load pf., rated power(KW) of the transformer cannot be a satisfactory one.

For a example.,

Consider a load(motor) of 1KW connected to the transformer end.The rated voltage and current value of motor are 100V & 10A a unity power factor load.

If the power factor of the load Is reduced to 0.5 then current flowing through the load will increase to 50A, supplying a constant of 1KW.

If cosØ is further reduced to a low power factor of 0.1, then naturally the current consumed by the load or supplied by the transformer will be 100A. This may damage the coils o the transformer.

 

Thus for safety of the system, out of V,I& cosØ only rated V & rated I are specified

That is why the transformer rating is mentioned in VA not in KW .

 

Hope you get cleared from this...If you have any doubts regarding this topic ask me in comment section.


                                       TAKE CARE....BYE!

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