Power generation - power factor

[rja211077]

With regard to stationary, industrial type engines, they are rated for their power output in terms of KVA or kW, where kW/KVA is a power factor (PF). I always learnt at school that power was just voltage x current so why the need for this PF? I have also only come across two values for PF - 0.8 and 1. Why are engines made with these two PFs predominantly?

[Turtle]

You're quite right, power does equal voltage x current but this only applies either to DC circuits or to AC in a purely resistive circuit. In a purely inductive AC circuit the current lags the voltage by 90 degrees, in a purely resistive AC circuit the current is dead in phase with the voltage and in a purely capacitive AC circuit the current leads the voltage by 90 degrees. In the real world, most loads are a combination of inductive and resistive elements and this produces loads where the current lags the voltage by an undetermined angle. Remember the power factor is calculated by taking the Cosine of the lag angle. Hope this helps