By far we have come to know what is power factor , power triangle, need of reactive power in our system.

But a big question arises , what is the need of all these?Why should we be concerned about it?

With increase in so much inductive loads, the power factor of the system is decreasing.Since power consumed depends upon this power factor.

Causes of low power factor:-

• The ac motors that we use are of inductive type. Due to inductive load, the current lags the voltage by huge angle thus ɸ increases and cosɸ decreases.
• The industrial electric discharge lamps ,arc lamps, heating furnaces operate at a low lagging power factor withdrawing more current from the system.
• Variable load.
• Harmonic current is a huge reason behind low pf.
• Even tranformers lead to a low pf.

Disadvantages of low power factor :-

• Greater size of conductor: Keeping the power fixed, at constant voltage the conductor will have to carry more current at low pf. This requires large conductor size.  

• Large kVA rating: kVA rating of the equipment is inversely proportional to pf. The smaller the pf, the larger is the kVA rating. Thus at low pf, the kVA rating of the equipment has to be made more, making the equipment larger and expensive. 

• Lower voltage regulation: The low lagging pf causes larger current to flow thus leading to voltage drops. Thus voltage at receiving end reduces than the sending end leading to lower voltage regulation.

• Larger copper loss: Larger current  causes more IR losses all the elements of the supply voltage. This results in poor efficiency.

• Reduced handling capacity of system: The lagging pf 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.

Need of power factor improvement :-

• From consumer’s end: A consumer has to pay electricity charges for his maximum demand in kVA plus the units consumed. If the consumer improves the pf, then there is a reduction in his max kVA demand and consequently there will be annual saving due to max demand charges. Although pf improvement involves extra annual expenditure on account of pf correction equipment, yet improvement of pf to a proper value results in the net annual saving for the consumer.

• From generating station’s end: A generating station is as much concerned with power factor improvement as the consumer. The generators in a power station are rated in kVA but the useful output depends upon kW output. As station output is kW= kVA ×cosɸ, therefore, number of units supplied by it depends upon the pf. The greater the pf of the generating station, the higher is the kWh it delivers to the system. This leads to the conclusion that improved pf increases the aesrning capacity of the power station.

Now the question is  how will we do that ? How to achieve an improved power factor ?

Power factor improvement can be done by using the following equipments:-

• Static capacitor: The pf can be improved by connecting capacitors in parallel with the equipment operating at lagging pf. The capacitor draws a leading current and partly or completely neutralizes the lagging reactive component of load current. This raises the pf of the load. For 3 loads, the capacitors can be connected in delta or star. Static capacitors are invariably used for pf improvement in industries.

Real image of capacitor bank

• Synchronous Condenser: It takes a leading current when over-excited and thus behaves as a capacitor. An over-excited synchronous moor running on no load is known as a synchronous condenser. When such a machine is connected in parallel with the supply, it takes a leading current which partly neutralizes the lagging reactive component of the load. Thus the power factor is improved.

• Phase advancers: Phase advancers are used to improve the pf of induction motors. The low pf of an induction motor is due to the fact that its stator winding draws exciting current which lags behind the supply voltage by 90. It provides exciting ampere turns to the rotor circuit at slip frequency. By providing more ampere turns than required, the induction motor can be made to operate on leading pf like an over-excited synchronous motor.