Low power factor has several disadvantages in power system. The main effect of low power factor is to increase the current and hence increase losses. This reduces overall system efficiency. Low power factor is thus not desirable from economic point of view.
Let us first understand the basic cause for low power factor. We know that,
Power Factor (pf) = cosØ
Thus more the value of cosØ, better will be the pf. In other words, lower value of Ø gives better pf. Let us now consider the impedance triangle as shown below.
It is clear from above triangle that as the value of inductance increase from X1 to X2, the angle Ø increase. This means that pf (cosØ) is decreasing. Therefore, increase in inductive load increases causes low power factor.
Causes of Low Power Factor:
Following are the main causes of low power factor:
1) The basic reason behind the low power factor is increased demand of reactive power. If at any point in the system, there is a balance between reactive power demand and generation then the power factor at that point will be unity. Inductive loads like Induction Motor draw lagging current and hence reactive power for the generation of magnetic flux in its air gap. Thus inductive loads requires reactive power. To meet this requirement, they draw very lagging current from the system and hence causes for the low power factor.
2) In industries, mostly induction motors either single phase, three phase or both are used. We know that induction motor operates at poor power factor. At no load or light load condition, the power factor varies from 0.2 to 0.3. But at full load condition, it operate at better power factor something around 0.85. Thus induction motors are one of the major cause of low pf.
3) The load on the power system is not always constant. It varies during the entire day. It is more during morning and evening but less during rest period of time. During light load condition, the supply voltage increases. This increases the magnetization current. This increase in magnetization current leads to low pf.
4) Apart from induction motors, various other kinds of load viz. Arc lamps, industrial heating furnace, discharge lamp etc. take lagging current. Hence they contribute to low pf.