POWER FACTOR EXPLAINED

Most electrical equipment creates an inductive load on the supply. This inductive load requires a magnetic field to operate, and when this magnetic field is created, the current will lag the voltage, i.e. the current will not be in phase with the voltage. Power Factor Correction compensates for the lagging current by applying a leading current, reducing the power factor to close to unity.

What is Power Factor Correction?
The power factor of a supply can be expressed as the cosine of the angle between Apparent Power and Active Power (cos ø). The diagrams below show the relationship between active, reactive and apparent power before and after PFC.

  Before After  
 
  • Inductive kVAr lags the Active Power by 90°
  • Apparent Power is the vector sum of Active Power and lagging Inductive kVAr
  • Power Factor is the cosine of angle ø
  • Capacitive kVAr now leads the Active Power by 90°
  • Apparent Power is the vector sum of Active Power + lagging Inductive kVAr + leading Capacitive kVAr
 
 
 
       

As angle ø is reduced, cos ø tends to 1 (unity power factor). Both apparent power (kVA) and total reactive power (kVAr) are significantly reduced.

Flattening the Hill
A good analogy is to envisage a person running along a surface. The gradient of the surface will influence the effort required. When the running surface is flat, then the angle ø between the horizontal and the slope is 0°. As cos 0° = 1, the runner achieves 100% efficiency, i.e. power factor = 1 and 100% of the energy burned is being used to run along the surface. However, if the running surface is steep, say at 25° to the horizontal, only 90% of the energy burned is being used to run as cos 25° = 0.9, i.e. power factor = 0.9. Therefore an extra 10% of energy is required. In laymans terms, PFC reduces the slope.

 
Jackson Switchgear, Unit 6C, Cian Park Industrial Estate, Drumcondra, Dublin 9, Ireland.
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