Monitoring True Power factor using DPM

Monitoring True Power factor using DPM
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Power factor is the cosine of angle between the voltage sine wave and the current sine wave. It is the ratio of True power (kW) to Apparent Power (kVA).

Power Factor (PF) = kW/kVA

Depending on which value of voltage and current we consider, there are different types of power factors:


1) Displacement PF - The power factor which is due to the phase shift between voltage and current at the fundamental frequency is known as displacement power factor.


Displacement PF = P/(V1I1)


2) Distortion PF - The power factor which includes the effect of harmonics present in the system is called distortion power factor.

Total Harmonic Distortion

3) True PF - It is defined as the ratio of average power to apparent power. Both the above power factors together combine to form the True power factor.


True PF = Displacement PF x Distortion PF


True PF = P/VrmsIrms

Understanding the various types of power factor is very important because all three have different implications.


True PF = Displacement PF x Distortion PF


Power factor improvement methods using capacitors will help to improve displacement pf. However, if the system is polluted by harmonics, it will reflect in lower distortion power factor. True power factor is the product of displacement and distortion power factor.[1]


Harmonic levels are measured as Total Harmonic Distortion (THD). Higher THD implies lower distortion PF. The graph here depicts the impact of THD levels on the true power factor of nonlinear loads.

Total Harmonic Distortion

The following table shows how different types of power factor vary with THD.

THD-IDisplacement PF (assumed to be compensated by equivalent Capacitors)Distortion PFTrue PF
5% 0.999 0.999 0.998
30% 0.999 0.958 0.957
40% 0.999 0.929 0.928

Overall, it will reflect in lower pf value. Hence, even if the displacement PF is corrected up to unity, the true PF will remain low because of poor distortion PF.


Our Digital panel meters have the flexibility to display displacement PF as well as True PF.

How to select True PF?

Digital Panel meters offers selection of PF types by means of VA selection methods. To achieve this, enter in programming mode of DPM and drill down to VA selection option.

Power Factor

1. Displacement PF

To display Displacement PF, select Vector Harmonics VA. Factory default is vector harmonics method.

MFM Displacement PF

2. True PF

To display True PF, select Arithmetic VA.


Arithmetic VA=Voltage*Current

APFC panels with detuned filters can effectively increase the displacement PF to unity. But true power factor will remain low due to low distortion PF. Thus, to improve distortion PF, Active Harmonic Filter should be used to mitigate harmonics.[1]


Monitoring of displacement or true power factors can be achieved using L&T Electrical & Automation’s Digital Panel meter series using the above selection method. To continuously monitor these, SmartComm EMS is recommended along with a host of other energy management benefits.


[1] L&T Electrical & Automation's VArticle Issue 33 - Harmonics and its impacts on power factor - Distortion Power Factor

About the Author

author

Rajesh R Shirodkar,

DGM-Corporate Communication

Rajesh Shirodkar is a seasoned marketing and business leader with over 20 years of experience in the automation and electrical industry, spanning marketing communications, sales, business development, and software solution selling. He has led successful brand transformation initiatives and high-impact marketing programs, including branding and account-based marketing campaigns, as well as industry events that drive visibility, engagement, and growth. With expertise in brand building, lead generation, solution selling, and sales enablement, Rajesh is known for translating technology and business offerings into compelling value propositions and delivering sustainable growth through strong stakeholder collaboration.

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