Latest QUCS 0.0.20 simulator includes a type of probe for measuring power.
I was trying to understand how it works, so I fed the power probe with two AC sources, one for current and the other for voltage. Both I and V sources are the same frequency, but with the phase angle between them adjustable.
The AC current source I1 has 1.2A RMS and the AC voltage source V1 has 1.5V RMS. The phase of the voltage relative to current, Ph, is swept between -180 and 180 degrees.
PF (dimensionless) - power factor, yellow trace
P (W) - active power, red trace
Q (VAR) - reactive power, blue trace
S (VA) - apparent power, magenta trace
I was expecting the apparent power S to change with the phase, too, just like the others.
Why is S constant no matter the phase between V and I?