Power factor

Power factor

The power factor of a circuit is defined in one of the following ways:

(i) Power factor = cos Ï• = cosine of the angle of lead or lag

(ii) Power factor = R/Z = Impedance / Resistance

(iii) Power factor = VI cos φ / VI

 = True power / Apparent power

Some examples for power factors:

(i) Power factor = cos 0° = 1 for a pure resistive circuit because the phase angle Ï• between voltage and current is zero.

(ii) Power factor = cos(±π /2 )= 0 for a purely inductive or capacitive circuit because the phase angle Ï• between voltage and current is ±π /2 .

(iii) Power factor lies between 0 and 1 for a circuit having R, L and C in varying proportions.