Ok -it's my turn - sorry - long
W = DC power or AC equivalent (true power)
VA = AC power (no allowance for power factor)
VAr = 'Bad' or wasted power
Try it this way - This should help you visualise what happens
Imagine 2 SINEWAVES exactly CO-INCIDENT (one for VOLTAGE, one for CURRENT)
Now ignore the bottom halves (just to make it easier to see)
This is the situation when the PF is UNITY (voltage and current in phase)
Consider The POWER (VA) consumed by the LOAD as the AREA under the half sinewave
In this case W is the SAME as VA, VAr is ZERO
Now SHIFT one of the sinewaves sideways a bit - this is what happens with a NON-LINEAR or 'reactive' LOAD (motors,transformers,capacitors etc)
The voltage and current are now 'out of phase'
The TOTAL area of the sinewaves is now LARGER - this is the POWER that the GENERATOR has to PRODUCE -kVA
The OVERLAPPING portion of the sinewaves is SMALLER - this is the POWER that the LOAD usefully CONSUMES -kVA
The DIFFERENCE between the two is kVAr - WASTED POWER (needs a bit of trig. to make the numbers add up)
I.E. large phase difference between voltage and current = low PF = greater power wastage
Why does this happen and where does the wasted power go ?
The generator still has to produce the current even if it is not used efficiently.
The current just warms up the generator and the aircraft wiring (and burns more fuel).
Most aircraft systems have the means to 'correct' the power factor i.e. bring the voltage and current back in phase with each other.
Who's next ?
Wraftongate