Power Factor:

Power factor (pf) is the ratio among true power and apparent power. True power is the power consumed through an AC circuit, and reactive power is the power in which is stored in an AC circuit. Cosθ   is known as the power factor (pf) of an AC circuit.  Where is the phase angle among the applied voltage and current sine waves and also among P and S on a power triangle it is the ratio of true power to apparent power.  Given Equation (9-4) is a mathematical representation of power factor.

Cosθ = P/ S                                                                (9-4)

where

cosθ = power factor (pf)

P = true power (watts)

S = apparent power (VA)

Power factor also determines what part of the apparent power is real power.  That  could  vary from  1,  when  the  phase  angle  is  0°,  to  0, whenever the phase angle is 90°.  The current lags the voltage and is said to have a lagging power factor in an inductive circuit, as display in Figure.

Figure: Lagging Power Factor

Within a capacitive circuit, the current leads the voltage and is said to have a leading power factor, as display in Figure.

 Figure: Leading Power Factor

A mnemonic memory device, "ELI the ICE man," could be used to notice the voltage/current relationship in AC circuits. The ELI refers to an inductive circuit (L) where current (I) lag voltage (E) and the ICE refers to a capacitive circuit (C) where lead voltage (E) current (I).