Benefits of Power Factor Correction in RLC-Type Circuits

Fundamentals

Discuss the benefits of power factor correction in RLC-type circuits (motors, generators, control networks, etc.) for commercial users and dangers of over-correction. Make sure to refer to practical examples and include calculations to back up your arguments from performance and financial points of view. 

Inductive load is the most common load and found in variety of applications such as generators, transformers and induction motors. These loads contain a kind of winding, which creates electromagnetic field to drive motor or transformer.  Electrical power is needed to maintain this electromagnetic field and it is called Reactive power. The actual work is performed by the remaining portion of total power known as Active power. The sum of active and reactive power is called Apparent power.

Power Factor: Power factor gives the important association among the three powers- active, reactive and apparent power. Basically, it signifies how efficiently electrical power is consumed. Higher the value of p.f., more better and efficient is the use of electrical power. (ABB Inc. Low Voltage Products 2015)

Figure-1: Relationship among Power factor, active, reactive and apparent power.

Power factor reduces (increase in angle Φ) with increasing reactive load. The relationship between apparent and active power is geometrically represented by right angle triangle shown in figure

Power factor correction: Power factor can be boosted by connecting power factor improvement capacitors in parallel with the system working at lagging power factor. In three-phase systems, delta or star connections of these capacitors can improve the power factor of the system. These capacitors contribute to the generation of reactive current and thus, provide reactive power to the inductive load. This helps in reducing the total apparent power (kVA) needed from the distribution network. (MOHANKUMAR 2010)

In Figure-2, the capacitance value C of power factor capacitor is calculated as follows.

Power distribution companies usually put penalty on industrial users if the p.f. is below the threshold (0.80 to 0.85); power factor correction can be used to avoid this penalty.

Many electric utility companies charge on the basis of ratio between highest apparent power and active power. Obviously a low p.f. will lead to higher apparent power and thus high cost. Power factor correction will help reducing the apparent power and also the cost of electricity bill.

Load using reactive power needs reactive current as well. Correcting the Power factor reduces this current. This arrangement can help in allowing circuit to add new loads. This addition of new load of course, requires more handling capacity.

Better power factor results into lower current in the conductors and therefore lower voltage drop. This essentially means the voltage of the electrical equipment gets better and improved.

Power factor correction results into lower current and lower conductor loss. (INTERSTATES 2017)

If, instead of power factor capacitor being connected across the inductive load, it is connected close to the supply, then, overcorrection of power factor occurs. This condition might cause a very high current to flow through the load, causing damage to the load equipment (MOHANKUMAR 2010)

References

ABB Inc. Low Voltage Products (2015) ‘Power factor improvement: Application guide’, 3-4. Accessed 23 January 2020 <https://library.e.abb.com/public/7b6d7029fb4e477b85909310dc2ef239/CAABB%20PFI%20App%20Guide%20Jun%202015.pdf>

INTERSTATES (2017) ‘5 Benefits of Power Factor Correction That Can Impact Your Utility Bill’. Accessed 23 January 2020 <https://www.interstates.com/power-factor-correction/>

MOHANKUMAR, D. (2010) ‘Power Factor Correction’. Accessed 23 January 2020 <https://www.electroschematics.com/power-factor-correction/>