Power Factor

Power factor is the ratio of the real power (W) or average power and the apparent power (VA) and it is symbolized by PF.

In the sinusoidal case, the power factor is simply cos (theta - phi), where (theta-phi)is the angle by which the voltage leads the current. It can also be computed by cos (theta L), where (theta L) is the angle of the total impedance of the circuit.

For a purely resistive load, the voltage and current are in phase, (theta - phi) is zero and the PF is unity (1). In other words, the apparent power and the average power are equal. Unity PF, however, may also be achieved for loads that contain both inductance and capacitance if the element values and the operating frequency are carefully selected to provide an input impedance having a zero phase angle. A purely reactive load, will cause a phase angle difference between the voltage and current of either plus or minus 90o, and the PF is therefore zero.

Power factor can also be lagging or leading. Leading and lagging refers to the phase of the current with respect to the voltage. Thus, an inductive load will have a lagging PF and a capacitive load a leading PF.


By: Jonald Sarmiento