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Controlling the Impact of Power
Factor and Harmonics on Energy
Efficiency
By Jacques Schonek
Power Business

Summary
Executive Summary
...
p 2
Identifying and analyzing problem areas
...

Harmonic mitigation and PFC solutions
...
p 7
Harmonic mitigation of Variable Speed Drives (VSD)
...
p 9

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Executive summary
A Power Factor Correction (PFC) and harmonics mitigation plan will always
improve the energy efficiency of electrical installations
...

This paper analyzes PFC and harmonics problem areas and offers practical
approaches for improvements
...
This paper is written to assist electrical installation designers
in identifying out-of-phase and voltage distortion problem areas
...
The goal is
to leverage existing and new technologies to decrease OPEX and to improve
energy efficiency within the site’s power infrastructure
...


with the same active power P transmitted to the
load
...
7 or THDi = 100 %, the r
...
s
...


the signal signs are opposite
...
The relevant parameter is

to the square of the r
...
s
...


cosine of the phase angle j between voltage and

These additional power losses mean more CO2

current (cos j)
...


When a current is distorted, the instantaneous
power fluctuates significantly
...


the current is undistorted
...
The Total Harmonic Distortion

resulting in voltage distortion
...


results
...
m
...
(root-mean-square) current
...

The Power Factor (PF) has been introduced to
assess this phenomenon
...

Figure 1

I

V

Sample situations impacting
power factor
...
71
Irms= 1
...
7
THDi= 0
PF = 0
...
43 x I

COM-POWER-WP02EN Rev1 | 

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Harmonic mitigation and PFC solutions
Numerous approaches can be deployed to
address harmonics and power factor issues in a
facility
...


Capacitor banks
Capacitor banks (see Figure 2) improve Power
Factor Correction and help to avoid reactive

Gh/Sn

energy penalties charged by the utility
...


Figure 3 – Selection criteria
...

When Gh/Sn exceeds 25 %, a series reactor
is necessary to protect the capacitors against
harmonic currents
...

Figure 2 – Example of low voltage capacitor banks
...
These filters consist of

Gh: total power of the non-linear loads,

reactors and capacitors set up in a resonant circuit

Sn: rated power of the supply transformer
...
A system may

Different types of equipment must be selected

be composed of a number of filters to eliminate

depending on the level of the network harmonic

several harmonic orders
...
The selection is based on the value of
the Gh/Sn ratio, as illustrated in Figure 3:

Active filters
Active filters are systems employing power

The active filter injects, in opposite phase, the

electronics which provide the harmonic currents

harmonics drawn by the load, such that the line

required by nonlinear loads thereby avoiding

current remains sinusoidal
...

COM-POWER-WP02EN Rev1 | 

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Hybrid filters
Hybrid filters are systems that include a passive
filter and an active filter in a single unit
...

Figure 4 - Examples of active and hybrid filters
...


Compensators" (HVC)
...
When

for the drive is considered standard
...
Multi-pulse solutions are

for each individual drive is recommended
...


enables use of cost effective mitigation solutions,

3-winding
transformer

such as active filters, for example, at the time of
installation (see Figure 5)
...
Combined with an
advanced control algorithm, this solution is suitable
for applications with low over-torque requirements
like centrifugal pumps, fans and HVAC machines
...


An Active Front End (AFE) is the best performing
solution concerning harmonic mitigation with
drives, limiting the THDi below 5 % (see Figure 7)
...
No detailed system evaluation is necessary,
making this solution the easiest to implement
...

Line-filter

Figure 5 – Chokes for drives
...

A precondition is a dedicated transformer directly

Figure 7 - Active Front End configuration
...
The use of a 3-

COM-POWER-WP02EN Rev1 | 

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Designing for energy efficiency
In the domain of electrical installations, energy

PFC and harmonic mitigation impacts all 3 aspects

efficiency is defined as follows:

of energy efficiency in the following ways:

•

•

energy savings: reduction in energy

Reduction of the power losses in transformers,

consumption

cables, switchgear, motors, capacitors

•

•

energy cost optimization: reduction in the cost of

Reduction of the demand power (in MVA),

energy paid to the utility

resulting in lower electrical bills

•

•

availability and reliability: reduction in the risk of

outage, and efficient equipment operation
...


Parameters to be considered
In order to better manage harmonics, the following

Project drivers

parameters should be considered:

Whenever an investment is necessary, it is
important to set a priority concerning the project

Network parameters

drivers
...
Performance

of the power network in order to be able to

specifications for a solution will also impact both

accommodate conditions at the Point of Common

Capex and Opex
...


The contractual arrangements with energy

The system size (known by power or impedance)

suppliers can also influence the design of the

and topology both have an influence on the

installation
...


energy limits are in place, the implementation
of Power Factor Correction capacitors should

Industry

be considered
...
Relevant standards in residential,

(resonance phenomenon)
...
Thus,

applicable to pieces of equipment
...


individual component level
...


power
The higher the share of non-linear loads compared

Applicable harmonic standard

to the total load power of an installation, the higher

Once industry and network parameters are

the necessity for evaluation of harmonics
...
Exceeding the standard requirements,
however, will result in a higher investment than
is needed
...

COM-POWER-WP02EN Rev1 | 

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Harmonic mitigation of Variable Speed
Drives (VSD)
The installation of Variable Speed Drives (see

•

Figure 8) should take into account the following

as no significant reactive energy is requested

considerations:

anymore by the VSD driven motor

•

•

if the motor driven by the VSD is newly installed,

the Power Factor Correction has to be revised,

the impact of harmonics has to be analysed,

the availability of power from the supply system

both in terms of possible disturbances and

should be checked

compliance to standards
...
Check impact on existing equipment of

harmonics mitigation solution should include the

installation

following three steps:

When a new non-linear load is connected to

1
...
The

connected on the same network
...
Below

a global installation
...


harmonic filter), there is a risk of overload and

if capacitors are already present in the

resonance introduced by the additional harmonic
2
...
Usually the supplier of the PFC or passive

advisable, consider equipment mitigation first

filter is able to evaluate the situation and should be

For drives totalling a power load of up to 100 kW:

contacted first
...
The standard solution

installed filter can be kept unchanged if it is

is to use AC-Line or DC-link chokes
...
Otherwise, the passive element

about 1,000 kW:

must be redesigned, as it is not possible to

•

in this power range, it is advisable to have the

connect another element in parallel with exactly the

transformer power equal to at least 2
...


drives load
...


must always be equipped with line chokes
...
No risk is introduced by the

with a dedicated transformer directly supplied

additional harmonic currents as the active filters

from the MV network
...
However,

commonly used, providing a 12-pulse supply for

the cancellation of harmonic currents may not be

the drives
...
In

be deteriorated
...
This allows for easy

contacted first
...


COM-POWER-WP02EN Rev1 | 

Controlling the Impact of Power Factor and Harmonics on Energy Efficiency

Conclusion

Power Factor and harmonics, because of their
impact on energy efficiency, are important issues
to consider for the management of electrical
installations
...

Solutions for Power Factor Correction and
harmonic mitigation have been presented in a
practical way, answering basic questions frequently
asked by electrical installation designers
...
In addition, both of these best practices
encourage the use of total system capacity in
electrical installations thereby increasing payback
on investment
...
schneider-electric
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Schneider Electric Industries SAS



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