In the expression for power P = VI cos θ, the term cos θ is known as power factor, its value lies between 0 to 1.
It can be defined as
- Cosine of the angle of lead or lag between current phasor and voltage phasor,
- The ratio =True Power/ Apparent Power = Watts/Voltamperes
- The ratio R/ Z = Resistance/ Impedance
For a constant load power P and system voltage V, current and VI requirement vary inversely as the load power factor. A lower value of p.f leads not only to increase cost of power supply equipment but also to enhance voltage drop and power losses in supply lines because of the increased line current. High value of p.f is a desired operating condition in power supply system.