Power factor refers to the cosine of the angle between the voltage and the current. In AC circuits, the nature of the load determines the power factor. Power factor is a critical parameter in AC circuits as it determines the amount of current which goes into delivering a certain quantity of power. Equipments which run at a lower power factor draw a high current for the same amount of load. What causes Power Factor All Electric loads can be categorized into three types, viz. Resistive, Inductive and Capacitive loads. Consider an AC voltage being applied across a simple resistor, the current drawn will be 'in phase' with the voltage. That is, the current reaches maximum when the AC voltage reaches maximum and falls to the minimum when the current reaches minimum.

In a purely inductive circuit, the current lags behind the voltage by an angle of 90 degrees. Thus the current is zero when the voltage is maximum and rises to the maximum when the voltage falls to zero.

In a capacitive circuit, the current leads the voltage by 90 degrees.

The angle between the current and the voltage is called the phase angle. The cosine of the phase angle is called the power factor. In the next article we will see the relation between power factor and kW and why power factor control is necessary