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Why the rating of generator is given in KVA & rating of motor is given by KW? View All


13 years ago - 2 months left to answer. - 1 response - Report Abuse
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phil
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).


13 years ago

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