Electrical Difference

cos φ.

In an AC circuit, the voltage and current waveforms may out of phase with each other by angle φ. The VA is simply V × A. However, the power, Watts, is W = V × A × cos φ.

That's just a quick start on this topic.

KW is nothing but active power

where KVA is Apprarent power

Friend,

It was a puzzle for me when I first started to learn circuit theory (decades ago...). You start with DC theory and learn the names of the units. In DC, volts times amps equals watts. Simple.

The confusion starts when you deal with AC circuits. Now, the volts and amps are rising and falling in (usually) a sine waveform. If your load is entirely resistive, then you still have the same relationship as in DC. However, the moment you include inductive or capacitive elements, then the volts and amps no longer rise and fall in "lock step" with each other. The technical term is that they are "out of phase". Thus, when the volts are at their peak, the amps are somewhere either ahead or behind their peak. The difference between these two peaks is called the phase angle. Mathematically, you have to correct the DC formula to include the effect of this phase angle difference. This correction is the cosine of the phase angle, or cos Θ (Θ is the Greek letter, theta, and is used to represent the phase angle in degrees between the peaks of the two amps and volts).

Thus, in DC W = V * A, but in AC W = V * A * cos(Θ).

--JMM

kVA is all the power you need, kW is the power that is actually doing all the work. Hence, the importance of power factor correction.

I got the picture clear when somebody said it is like a glass of beer.

Real power (kW) is the liquid, Reactive power (kVAr) is the foam and the whole thing inside the glass is the complex power (kVA)