why transformer power is always given in KVA not in watts?Explain please...

Question

anonymous · Answer

If VA stands for what I think it does, which is volt-amps, then KVA is the same as Kilowatts. Recall how electrical power is calculated.

anonymous · Answer

KVA stands for Kilo Volt Amps represents the unit of "Apparent Power". There is a power triangle in electric circuits terminology which has three components i.e True Power , Apparent power and Reactive power. Apparent Power = True Power + Reactive Power. True power unit is watts ( Kilo watts) which is actually useful and consumed. All our loads  i.e are rated fans , tv, bulbs etc with true power. Since these are not purely resistive loads they have a power factor and draw reactive power. True power = Voltage * Current * PF
lets us take load True power is 100 watts and Voltage is 10 and PF = 0.5 then current drawn is 20 watts. If you design the transformer  in this case for true power rating it will be able to supply only 10 amps of current in contrast to 20 drawn by load. For safe operation the transformer should be designed for more than 200 VA . In order to account for power factors they are designed for KVA.

shiraz14 · Answer

And PF can vary based on the resistance of the setup and the coil. Also, @alex_ind, there's a slight typo - the current drawn should be 20 amps.