Effect of Harmonics on Power Factor

Effect of harmonics on Power Factor

Power factor

• It is defined as the ratio of cosine of voltage vector and current vector.

                      OR

• It is defined as the ratio of active power ( kW ) and apparent power       ( kVA ).

       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 / V_RMSI_RMS

                                     = 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

• When the system is affected by harmonics due to Non linear load, the RMS current increases.

        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.

You may also like :

What do you mean by AC Drive?

Inspection Report of Low voltage Installation

What do you mean by Linear Load and Non – Linear Load?

What do you mean by Low voltage, Medium voltage and High voltage?