Harmonic distortion indicators - Power factor

Definition

The power factor PF is the ratio between the active power P and the apparent power S.

[math]\displaystyle{ PF=\frac{P}{S} }[/math] 

Among electricians, there is often confusion with:

[math]\displaystyle{ \cos \phi=\frac{P1}{S1} }[/math]
Where
P1 = active power of the fundamental
S1 = apparent power of the fundamental
The cosφ concerns exclusively the fundamental frequency and therefore differs from the power factor PF when there are harmonics in the installation.

Interpreting the power factor

An initial indication that there are significant amounts of harmonics is a measured power factor PF that is different (lower) than the measured cos ϕ.