What is power factor? What are the effects of low power factors? Write down the methods of power factor improvement?

Power factor. The cosine of angle between voltage and current in an a.c. circuit is known as power factor.

Effects of low power factors : 

The power factor plays an importance role in a.c. circuits since power consumed depends upon this factor.

P_ph =V_phI_ph cos$\phi$ [For single phase supply]

$\Rightarrow I_{ph}= \frac{P_{ph}}{v_{ph} \cos \phi }$

$P_{3 - \phi } =V_L I_L Cos\phi$

$I_L= \frac{P_{3 - \phi }}{V_L Cos\phi }$

It is clear from above that for fixed power and voltage, the load cu current is inversely proportional to the power factor. Lower the power factor, higher is the load current and vice-versa. A power factor less than unity results in the following disadvantages:

(i) Large kVA rating of equipment: The electrical machinery (e.g., alternators, transformers, switchgear) is always rated in kVA.

Now, kVA = $\frac{kW}{\cos \phi }$

It is clear that kVA rating of the equipment is inversely proportional to power factor. The smaller the power factor, the larger is the kVA rating. Therefore, at low power factor, the kVA rating of the equipment has to be made more, making the equipment larger and expensive.

(ii) Greater conductor size: To transmit or distribute a fixed amount of power at constant voltage, the conductor will have to carry more current at low power factor. This necessitates large conductor size.

(iii) Large copper losses: The large current at low power factor causes more I'R losses in all the elements of the supply system. This results in poor efficiency.

(iv) Poor voltage regulation: The large current at low lagging power factor causes greater voltage drops in alternators, transformers, transmission lines and distributors. This results in the decreased voltage available at the supply end, thus impairing the performance of utilization devices. In order to keep the receiving end voltage within permissible limits, extra equipment (i.e., voltage regulators) is required.

(v) Reduced handling capacity of system: The lagging power factor reduces the handling capacity of all the elements of the system. It is because the reactive component of current prevents the full utilization of installed capacity.

Methods of power factor improvement : 

(i) Static Capacitor 

(ii) Synchronous Condenser 

(iii) Phase Advancer