Why the rating of generator is given in KVA & rating of motor is given by KW?
All electrical devices that supply power are usually rated in kVA. This includes transformers, UPS’s & the like.
Simply put, the difference between kVA & kW is that kVA is “Apparent Power”, which does not take into account the Power Factor & kW is “True Power” . See the below equations:
VA = E x I
W = E x I x Cos phi
The above equations are only for single phase.
When a manufacturer makes a transformer, generator, UPS etc, they have no idea of the type of load that will be used & consequently can only rate the device according to its maximum current output that the conductors can safely carry (at untiy Power Factor) & the insulation rating of the conductors (voltage & temperature).
Example.
A single phase transformer capable of delivering 100 Amps at 500 volts would be rated at 50 kVA:
500 x 100 = 50 000 VA (or 50 kVA).
If the Power Factor of any given load was 0.5, the “True” power output of the transformer would be 25 kW:
500 x 100 x 0.5 = 25 000 W (or 25 kW).
