Power Factor Correction

 Most loads in modern electrical distribution network are inductive and resistive loads. 

Resistive loads are loads that convert all form of energy to heat and they always have heating element incorporated in there design. Examples include: Incandescent bulb, heater, cooker etc.

Resistive Load:

Resistive loads require one type of current -

- Working power (kW) which is used to perform the actual work of creating heat, light etc

Inductive Load:

Inductive loads are loads that operate base on the principle of electromagnetic induction. They always have coils in them. 

Example includes: Transformers, electric motor, fan etc.

When a current is supplied to an inductive load. It converts this current to magnetic using the coil inside it. Because it is an inductive load, current lags voltage by an angle of 90 degree.

Inductive load requires two kinds of current:

- Working power (kW) to perform useful and actual work of creating heat, motion, machine output etc

- Reactive power (kVAR) to sustain the magnetic field (to make the system keeps working)

Working power consume watts while reactive power doesn't perform useful work but helps in circulating magnetic energy within the system as it is in operation (example - generator, electric motor etc).

Working power and reactive power together make up apparent power. Apparent power is measured in kilovolt-amperes (kVA).

 Where apparent power (KVA) is the total power in an AC circuit that is both dissipated and absorbed.

Formula -

kW 

P = I x V (single phase DC)

P = I x V x cos(phi)  (single phase AC)

P = √3 x VLx IL x Cosθ  (three phase AC)

Power Factor Calculation-

PF = working power / apparent power

What does it mean to have low power factor

Low power factor means that the equipment (generator or electric motor etc) is not utilizing all the electrical power it is consuming (electric motor) / not supplying all the electrical generated energy (generator or transformer).

For the above figure - 

As the triangle relationships shown above, kVA decreases as power factor increases. At 70% power factor, it requires 142kVA to produce 100kW. At 95% power factor, it requires only 105kVA to produce 100kW. Another way to look at it is that at 70% power factor, it takes 34% more current to do the same work.

Improving Power Factor - 

When apparent power is greater than true/working power (kW), the utility must supply the excess reactive current plus the working current. 

Power capacitors act as reactive current generators by providing the reactive current, they reduce the total amount of current the system must draw from the utility.

Benefits of Capacitor Bank -

- Improved voltage

- Reduce electric utility bills

- Increase system capacity

- Reduced system losses

Where to Install Capacitor Bank for Load - 

The best place to install capacitor bank is directly parallel to the device (electric motor etc) where kVAR is consumed

Where to Install Capacitor Bank for Feeder - 

When correcting entire plant loads, capacitor banks can be installed at the service entrance, if load conditions and transformer size permit. If the amount of correction is too large, some capacitors can be installed at individual motors or branch circuits.