Shaikh Shamser J.

Electrical Systems 21-1 (2025): 74-85

Ali *1
Regular paper

Harmonic Mitigation in
Economical Way: A Case Study.
Harmonics is the reality today in every facility. There are many myths and
confusion about the right way to mitigate harmonics in the power
distribution system. Harmonics mitigation is a challenge and it becomes
more complicated with an operating facility having a power distribution
system with an automatic power factor correction system (APFC Panel).
This case study evaluates various options that any facility’s management will
have for an economical yet effective harmonic mitigation option. It is a case
study in actual application at a small manufacturing facility in Tamil Nadu.
The requirement was mandatory to meet the TANGEDCO (Tamil Nadu
Generation & Distribution Corporation Ltd.) set harmonics target to avoid
the penalty. A step-by-step approach was taken to study the existing
situation, analyze the data, and weigh the pros and cons of various options
to select an option to meet the requirements. The study outcome proved
convincingly that for any operating facility having an automatic power factor
correction system, the best option is to first convert the existing system into
a de-tuned passive harmonic filter in situ and then evaluate further for
necessary corrective actions, if any, for further harmonic mitigation plans.
It is not only cost-effective but also convenient as it does not affect the
ongoing operations of the facility, be it manufacturing or commercial.

Keywords: Harmonics Mitigation, Tuned Passive Harmonic Filter, De-tuned Passive

Harmonic Filter, Automatic Power Factor Correction System, Active Harmonic Filter,
Power Factor.

1. Introduction

Traditionally electrical power distribution system design was with an automatic power
factor correction system using a power capacitor to compensate the reactive power losses so
that the actual power factor can be maintained very close to unity(21). It was needed
because the load was mainly inductive type and the machine control system was
straightforward and without much use of semiconductor components (11). Over time and as
technology developed the usage of semiconductor components in the machine control
circuit increased which led to the uneven current drawn resulting in harmonics generation.
An increase in harmonics in the distribution system will have many cascading effects which
will also increase the risk in the facility's operations (2). Due to this practical operational
problem, the consultants started designing the power distribution system with de-tuned
passive harmonic filters instead of an automatic power factor correction system. The main

*Corresponding author: Shaikh Shamser Ali, Sr. Consultant Sams Consultant Chennai India Email
sams586@yahoo.co.in

1
Sr. Consultant Sams Consultant Chennai India

Copyright©JES2025on-line:journal.esrgroup.org
 J. Electrical Systems 21-1 (2025): 74-85

difference between the two is the addition of reactors into the system which will act like a
blocking circuit for the harmonic current. Therefore, the combined effects of the capacitor
and reactor will not only compensate for the reactive power loss but also block the
harmonic current to some extent (7). And this is the current practice in India across the
industries.

The systems supplied and installed in the last 15 years are de-tuned passive harmonic
filters. However, the systems supplied before that were automatic power factor correction
systems. Harmonic audits across the industries, whether new or old, show a higher level of
harmonics current. Every facility has 3rd, 5th, and 7th-order harmonic present over the
prescribed limit mainly due to the lighting load, battery charger, receptacle mount loads,
UPS, VFD, etc. which are common loads in every facility (9). The facilities having the
power factor correction systems are more affected due to higher harmonics current. In the
meantime, some of the state’s distribution companies introduced new policies to maintain a
certain limit of voltage and current harmonics instead of power factor. Failing to do so
leads to a huge penalty. TANGEDCO (Tamil Nadu Generation & Distribution Corporation
Ltd.)is one such state organization where maintaining harmonic current became the new
norm. It was done under the direction of a tariff order by the Tamil Nadu Electricity
Regulatory Commission (TNERC), wherein any HT consumer/generatorneeds to meet the
specified harmonic limits as per norms stipulated in CEA (Central Electricity Authority)
regulation on grid code (12, 13).

These facilities had options like replacing the existing system with a suitably designed
active or tuned passive harmonic filter, replace with a de-tuned passive harmonic filter, or
converting the existing system into a de-tuned harmonic filter and then deciding the further
actions. This paper evaluates these options through a case study in an actual application.
Harmonics are present in every facility due to the non-linear nature of loads and cause huge
problems for the safety and security of equipment and data. Mitigation of harmonics is a
need of the hour and many state Governments are seriously planning to implement penalties
for not maintaining a prescribed level of harmonics in their respective facilities in the
industry (17).

Harmonics is a matter of concern for both TANGEDCO and the industries as it affects both.
The bottom line is that it affects performances. Industries are concerned because it causes
unnecessary hindrances in operations due to equipment failure and data loss (30).
TANGEDCO is concerned because it affects their ability to provide clean and adequate
power to their customers. Harmonics mitigation is the way forward to overcome these
problems both on TANGEDCOs and the industry’s part. It is always better to mitigate the
harmonics at the machine level that generates the harmonics. Alternatively, it can also be
mitigated at the Point of Common Coupling (PCC) (23).

The presence of harmonics in electricity distribution companies not only increases

distribution losses in the system but also decreases the life of electrical equipment.
Malfunctioning of circuit breakers and relays, overheating of conductors and cables, and
premature failure of transformers, motors do have a root cause as harmonics in most cases
(5). If harmonics in the system are beyond a limit, the reliability of the electrical system
also decreases. All the above effects of harmonics have an impact on the overall operation
of consumer and distribution companies.

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 Shaikh Shamser Ali: Harmonic Mitigation in Economical Way: A Case Study

2. Harmonic MitigationOptions

There is a general perception among the industries that mitigation of harmonics is a capital-
intensive project (19). It becomes more complicated in an operating facility when it goes
for expansion and modernization. Fly-by-night operators are always there to create
confusion in the customer's mind for their petty gains. Some ill-informed professionals also
tend to create hurdles when the customers look for information to make a decision. There is
always a better way to mitigate harmonics because it is not one pill-for-all solution but a
tailor-made solution (4). This case study highlights one such specific case where the
solution was not only technically feasible but also commercially viable. Depending upon
the severity of harmonics, the type of harmonics, and the objective of the consumer, there
are several solutions available in the market that can meet the requirements. Each solution
has its benefits and limitations. Various harmonic mitigation techniques that are available
can be listed below (31). Few technologies need to be adopted at the design stage whereas
few technologies can be implemented as a retrofit or additional component/equipment.

 Line Reactors.
 Isolation Transformers.
 Tuned Passive Harmonic Filters.
 De-tunedPassiveHarmonic Filters.
 Active Harmonic Filters

As mentioned, each solution has its advantages and limitations. There is no single
solution that is better than other solutions. A careful and detailed study of the
harmonics in the system along with consumer requirements can result in the selection
of the best possible solution (24). The selected solution could be either one or a
combination of the few technologies mentioned above.The section below shows a brief
about each technology and its application.

Line Reactors

Line reactors are one of the simplest and lowest-cost technologies for the mitigation of
harmonics. These are used at the load end and in line with the load that is generating
harmonics. Line reactors are very common with variable frequency drives. They
operate on the principle of increasing the impedance of the circuit. If a plant has a 1000
kVA transformer with an impedance of 7% and a drive of 100 kVA. This drive will
have an approximate impedance of only 0.7%. As the transformer impedance will be
very small relative to each load, a line reactor in series will improve the impedance of
the circuit (32).One of the major advantages of a line reactor is its lowest cost and
reduction in harmonic levels to a greater extent. Another advantage is that since they
are installed right at the load end, harmonic distortion is reduced in the distribution
system (29). One of the limitationsof installing a reactor on the power distribution
system is the increase in the total percentage reactance of the circuit which will
decrease the power factor leading to a poorer regulation.

Isolation Transformer

The isolation transformer is one of the very effective means of not only mitigating
harmonics but also other power quality issues like transients, common mode noise, and
zero sequence currents. The operating principle of an isolation transformer is also

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based on a line reactor, which increases system impedance (34). The leakage
inductance of isolation transformers increases circuit impedance so that harmonics are
reduced to a great extent. Typically, a delta–wye configuration is used in isolation
transformers. Since, the primary is delta connected and the secondary is wye
configuration, zero sequence currents (Triplen harmonics) will not transfer to the
primary side of the network (8).Due to capacitive coupling between winding and shield
with proper grounding, transients, common mode noise, and zero sequence currents are
not reflected on the other side of the transformer. Isolation transformer has the added
advantage of eliminating other power quality issues in addition to harmonics over line
reactors. Their harmonic mitigation capability is the same as that of a line reactor but
can be very useful where zero sequence currents and other power quality issues as
mentioned above are present (38). Their cost of being around 5 -6 times higher as
compared to line reactors.

Tuned Passive Harmonic Filter

Tuned harmonic filters are a combination of capacitors and reactors (inductors) which
are connected in series to form a tuned circuit. This tuned filter is connected in parallel
to the main system. As the LC circuit is tuned to a particular frequency to form
resonance, it offers the lowest impedance to that particular frequency (harmonic).
Harmonic current instead of flowing to the utility, flows through the filter being low
impedance path.A tuned Harmonic Filter is specific to a particular harmonic
frequency(22).

De-Tuned Passive Harmonic Filter

This is like a general-purpose harmonic filter and not particular to any order of
frequency. Low pass filters or de-tuned filters can attenuate all order of harmonic
frequencies. De-tuned harmonic filters are a combination of series and shunt elements
of reactors and capacitors.The shunt circuit prevents the attraction of harmonics from
other sources where are series circuits filters of primarily 5th and 7th order harmonic.
They are one of the most economical means of mitigating harmonics (33).

Active Harmonic Filter

Active harmonic filters are the latest among all technologies for the mitigation of
harmonics. They continuously monitor the load current along with the fundamental and
harmonic current. Based on the order of harmonics and their magnitude, Active
Harmonic Filter will detect, generate, and inject an equivalent magnitude of individual
harmonics with a phase shift of 180 degrees (14). These injected currents will nullify
the harmonics in the system. Active harmonic filters can filter out harmonics up to the
50th order of harmonics. So Active Harmonic Filters need some energy to drive
themselves. As active filters use fast-switching IGBTs, they produce noise while
switching which can cause disturbances in the system. These noise signals can also be
harmful to the sensitive equipment. The presence of high voltage distortion can also
affect the performance of active harmonic filters. In terms of cost, they are the costliest
among all available options (41).Apart from the above technologies, some other
techniques apply the principle of de-rating where equipment is capable of handling
harmonics. One of the examples is K-rated transformers which de-rates a transformer
to withstand higher temperatures generated due to harmonics.

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 Shaikh Shamser Ali: Harmonic Mitigation in Economical Way: A Case Study

3. Methodology

A step-by-step approach (10) is adopted since it is a case study in real-life applications in

an operating manufacturing plant. The existing system is an automatic power factor
correction (APFC Panel) system as a standard power distribution practice in the industry.
The plant operating procedures and needs are understood by a plant visit to ensure a smooth
and non-interruptive action plan (20). The power quality and harmonics readings are
measured and recorded for an hour with normal plant operating conditions so that the same
can be compared against the readings taken after converting the existing system into a de-
tuned passive harmonic filter. A list is prepared for the components to be replaced to
convert the existing system. A new wiring diagram is prepared to ensure the correct
workmanship with the replaced and new components in the system. All materials are
procured and the new wiring is made as per the renewed wiring diagram. On the agreed day
the existing system is isolated and disconnected from the bus-bar so that the conversion
work can be done without any risk. The additional components like reactors are fitted inside
the panel, and replacement components like higher voltage-rated capacitors and contactors
are replaced. Additional exhaust fans are fitted on the panel for better heat extraction. After
the new components are fitted the new wiring is replaced with the old one. Once the system
conversion is done in situ a visual check is done to ensure everything is secured properly
and it is safe to do further tests (42). Cold checks and insulation checks are done before
connecting the new system which is a de-tuned passive harmonic filter back to the power
distribution system. Power quality and harmonics readings are again measured and
recorded for an hour with normal plant operating conditions. This reading is compared with
the earlier readings to decide whether there is any improvement in power quality and
reduction in harmonics content in the distribution system (28).

4. Plant Power Distribution System

The case study is done in one of the leading leather shoe manufacturing plants in Tamil
Nadu. The plant receives power at 11kV which is stepped down to 440 volts. The base
demand of the plant is 320 kVA where as the contract demand was 400 kVA. The average
registered demand during the last 12 months is around 328 kVA.The rated capacity of the
transformer is 500 kVA. The power distribution schematic is illustrated in Figure 1.

Figure 1: Single Line Diagram of Power Distribution System

Loads in the plant constitute mainly motors with drives. VFDs or drives are non-linear

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loads that generate harmonics and can get circulated into the power distribution system, if
not controlled, being a closed-loop system (15). TANGEDCO carries out routine
measurements at the consumer incomer being the Point of Common Coupling (PCC) and if
harmonics are found to be high, the consumer is asked to reduce the harmonics within a
given time.

The shoe manufacturing plant also got a notice from TANGEDCO asking them to
reduce the harmonics below the specified limit. The specified limit of current
harmonics is 8% and voltage harmonics is 5% by TANGEDCO. All HT consumers
must keep current and voltage harmonics as specified by the TANGEDCO. Based on
the notice, the shoe manufacturing plant carried out a detailed harmonic study of the
plant for further necessary actions.

5. Harmonic Study Summary

A detailed harmonic study is carried out in the plant by a contractor specializing in

harmonic mitigation. During the study, harmonics are measured at different nodes in
the plant at the following locations.
 Main incomer
 SSB – 1
 SSB – 2
 SSB – 3
 Lighting load
 Air Compressors

The harmonics readings at the main incomer node are discussed here since TANGEDCO
will monitor the same at this point.

Main Incomer (PCC)

At the main incomer being the PCC, measurements are taken with the system in “ON”
condition and “OFF” condition. Graphs in Figures 2&3 show current waveforms at the
main incomer when capacitors are “ON” and “OFF” respectively. The voltage waveform is
not shown because the readings are insignificant and within the limit.

Figure 2: ON Figure 3: OFF

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 Shaikh Shamser Ali: Harmonic Mitigation in Economical Way: A Case Study

It can be seen from the waveform that the current waveform is distorted when capacitors
arein “ON”condition.Figures4&5showthe individual order of harmonics with capacitors
“ON” and “OFF” condition.

Figure4: Individual Order of harmonics when capacitors are ON

Figure5: Individual Order of harmonics when capacitors are OFF

As seen from the above graphs when capacitors are in “ON” condition, the % THD
voltage and current are 3.28% and 13.53% respectively. When the capacitors are in
“OFF” condition, the % THD voltage and current values are 2.44% and 3.48%
respectively. Predominant harmonics are 5Th and 7Th.

The above measurements indicate that significant current harmonics are not generated
by the load but are amplified due to capacitor banks. The plant could not isolate
capacitor banks while capacitor banks were in “OFF” condition, the power factor
dropped to 0.79 from0.98 which would result in higher maximum demand by the plant
and a possible PF penalty. Table 1 shows a summary of measurements at other
locations in the plant.

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Table1: Summary of harmonic measurement

As seen from Table 1, the total harmonic distortion current at the main incomer is 13.53%
which is more than the limit specified by TANGEDCO. Measurements at different load
centers also show a higher % of THDi which is more than 8%. In terms of harmonic current,
major contributors are lighting load (29.49%), UPS (135.41%), compressors (11.92% &
10.24%), and SSB-2 (13.48%).Based on the harmonic measurement study, the plant
management needed to mitigate harmonics.

Selection of Solution

After carrying out a harmonic study and based on the outcome, the plant team decided to
mitigate harmonics. The next challenge for the plant team was to select a technology that
would be technically suitable and financially feasible. The plant team had mainly three
options available for the mitigation of harmonics. These three available options are:

 Active Harmonic Filter.

 New Passive Tuned Harmonic Filter
 De-tuned Harmonic Filter(Convert the existing APFC into a de-tuned filter in situ).

The plant team compared the above three technologies based on technical feasibility,
harmonic mitigation capability, ease of operation, maintenance cost, operating cost, and
initial cost.Table 2 shows a comparison summary of the above technologies.

Table 2: Comparison of various technologies

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 Shaikh Shamser Ali: Harmonic Mitigation in Economical Way: A Case Study

The harmonic spectrum of the plant consisted of mainly 3rd, 5th, and 7th order harmonics as
predominant harmonics. Other harmonics present in the system were 11th and 13th.Based on
the above comparison, the plant team opted for the third option and decided to convert the
existing APFC system intoa detuned harmonic filter of 100 KVAR capacity in situ.

Post Implementation Results

After converting the existing APFC system in situ and making it a de-tuned passive
harmonic filter, the plant team carried out harmonic measurements at the incomer. Figure 6
shows the current waveform after the installation of the detuned filter.Figure 7 shows
individual harmonic order.

Figure 6:Current waveform after installation of detuned filter

Figure 7: Individual orders of harmonics

Table 3 shows the summary of the mitigation result.
Table 3: Summary of the Result

As seen from the table, after the installation of the detuned harmonic filter, the total
percentage current harmonic distortion has come down to 4.69% from 13.53% which
is well below the limit specified by TANGEDCO.

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6. Conclusion

The plant management had 3 options to choose from. These are (i) active harmonic
filter in addition to the existing automatic power factor correction system, (ii)
replacing the existing automatic power factor correction system with anew tuned
passive harmonic filter, and (iii) converting the existing automatic power factor
correction system into a de-tuned passive harmonic filter in situ and then decide
further course of actions if needed. The first option would cost Rs. 8,00,000, the
second option would cost Rs. 4,00,000, and the third option would cost Rs. 2,00,000.
The plant management decided to first explore the third option. Post-conversion of
the existing automatic power factor correction system into a de-tuned passive
harmonic filter and further harmonic readings with the normal operating condition
resulted in a satisfactory level of harmonic which was within the IEEE limit (43) and
at the same time a very desirable level of power factor as shown in Table 3. The
highlight of the performance is the reduction of current harmonic to 4.69% from
13.53% while the power factor is 1. The third option is not only cost-effective but
also meets the requirements of the plant management without any compromise with
the day-to-day operations.

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