11 January 2020

Effect of Harmonics on Power Factor

Effect of harmonics on Power Factor
  • It is defined as the ratio of cosine of voltage vector and current vector.
                      OR
       Power Factor = kW / kVA
Displacement Factor ( Displacement Power Factor )
  • It is defined as the Cosine of angle between voltage vector and current vector at the fundamental frequency.
       Displacement Factor = P / V1I1
Distortion Factor ( Distortion Power Factor )
  • The power factor in which effect of harmonic of the system is considered is called as distortion power factor
  • It is ratio of fundamental RMS current to the RMS current of the total current.
       Distortion Factor = I1 / I
                                   = 1 / √ ( 1 + THD2 )
                   Where I1 = Fundamental current
  • Higher the value of total harmonic distortion, lower the distortion power factor       
True Power Factor
  • It is defined as the ratio of average power to the apparent power.
        True power factor = P / VRMSIRMS
                                     = Displacement Factor × Distortion Factor 
Capacitor banks
  • The improvement of the power factor is done by capacitor bank and in this case improvement done in the displacement power factor. 
  • The voltage and current waveform are at the fundamental frequency or say at 50 Hz.

Effect of harmonics on Power Factor
        I = I1 √ ( 1 + THD2 )
  • The kVA demands increases due to increase in RMS current but the kW output of the system does not change.
       kVA = kW / Power Factor
  • The power factor has to decrease if the kVA demand increases with kW remain unchanged. 
  • This power factor decrease due to presence of harmonics.
  • The true power factor remain low in spite of displacement power factor increases due to poor distortion power factor
  True power factor = Displacement Power Factor × Distortion Factor
Capacitor bank and Distortion power factor
  • The capacitor bank do not significantly improve distortion power factor. 
  • It can lead to harmonic resonance and harmonic amplification when harmonic present in the system. 
  • The harmonic amplification is avoided by using detuned reactors.
How to increase true power factor?
  • The true power factor is increased only if both displacement power factor and distortion power factor increases. 
  • The capacitor bank improves displacement power factor. 
  • The active harmonic filter must be used to improve distortion power factor in a system which consists of rich harmonics. 
  • The combination of capacitor and active harmonic filter is good combination for power factor improvement.
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