in the electricity
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in the electricity
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It should be 'kVA' and 'kW' - kiloVoltAmperes & kiloWatts.
AC power comes at a frequency of 50 or 60 Hz.
Normally because the load is reactive, the Voltage and Current waveforms have phase difference (angle 'theta'). The power delivered then, will be the component of one of them (either of the two) that is brought to the same phase of the other other (Cos(theta) component). Power gets consumed only for the components that are in phase.
We know that
P = V. I
and so for reactive load situation
P = V I Cos(theta) in Watts, W (or kW even).
But the total power that is released is the product [V I] expressed as 'Volt Amperes' (VA or kVA even) as different from the above-mentioned active (useful part) power (W or kW).
The factor 'Cos(theta)' is called 'power factor'
Cos(theta) = (kW)/(kVA).
It is the inductive loads like motors & transformers that pull down the active power making it less than its full potential of VA (or kVA). It is said to be 'current lagging' (with Voltage leading) and is compensated by adding a reactive load (that doesn't consume power) like 'Capacitors' (current leading) for power factor correction. Specially designed 'synchronous generators' (alternators) called 'synchronous condensers' are also used in the circuit at transmission stage.
kva = kilovoltampere is product of volts and current measured separately.
kw (there's no kwa)= kilowatts is useful power and is product of kva and cosine of phase angle between voltage and current.
kva is device rating, kw is consumption rating.
in pure resistive system kva =kw.
Kilovolt amps and Kilowatt amps,
http://en.wikipedia.org/wiki/Kilovolt-ampere
http://en.wikipedia.org/wiki/KW#Kilowatt
Good luck.