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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)
ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue II, February 2026
Investigation and Mitigation of Harmonic Distortion and Parallel
Resonance in an Industrial Power System Using ETAP
Rajvi Y. Matiyeda, Prof. Ajay M. Patel, Patel Harshkumar R.
Department of Electrical Engineering, Birla Vishvakarma Mahavidyalaya Engineering College, India
DOI:
https://doi.org/10.51583/IJLTEMAS.2026.15020000034
Received: 09 February 2025; Accepted: 14 Jan February 2026; Published: 05 March 2026
ABSTRACT
Harmonics, primarily generated by non-linear loads, can lead to voltage distortion, equipment overheating, and
reduced system efficiency. This project analyzes harmonic distortion in the electrical distribution network of a
cement plant using ETAP software. A detailed Single Line Diagram (SLD) was modeled, and harmonic load
flow analysis was conducted to evaluate Total Harmonic Distortion (THD) at key bus locations. A frequency
scan was performed to identify parallel resonance conditions, which were mitigated by installing series reactors
with capacitor banks. Additionally, passive filters were designed to reduce dominant harmonic components and
ensure compliance with IEEE 519 standards. The study demonstrates a significant improvement in power quality
and highlights ETAP as an effective tool for harmonic analysis and mitigation in industrial systems.
Keywords: harmonics, total harmonic distortion, capacitor bank, resonance, ETAP
INTRODUCTION
The cement plant draws its primary power from a nearby 66 kV grid substation through a 2.8 km long, 630
sq.mm single-core underground cable, with a contracted demand of 12 MVA. Power is imported via two 66/11.5
kV, 12.5/15 MVA transformers, with a % impedance of 8.22 and a vector group of Dyn11. The star points of
the transformers and the Waste Heat Recovery System (WHRS) generator are grounded through Neutral
Grounding Resistors (NGR) with a current limit of 100 A. The plant operates various non-linear loads such as
motors, crushers, and mills, which are common in cement production. In cement plant, operators often encounter
unexplained issues related to voltage instability and overheating of electrical equipment, especially in areas with
high-power-demand loads. One frequent cause of these disturbances is the interaction between the plant’s non-
linear loads and capacitor banks used for power factor correction. This interaction can lead to amplified voltage
fluctuations, causing equipment like motors and transformers to overheat, malfunction, or even fail prematurely.
Additionally, plant operators may notice that protective devices like relays and circuit breakers sometimes trip
unnecessarily or fail to operate correctly, resulting in unexpected shutdowns and increased downtime. These
problems typically go unnoticed until they cause significant operational disruptions.
The underlying cause of these issues is the harmonic amplification due to the interaction between the plant’s
electrical loads and the capacitor banks. Addressing these disturbances is critical to maintaining equipment
reliability, improving system stability, and reducing operational disruptions in cement plant operations.
Harmonics Study
Harmonic analysis was conducted to evaluate power quality disturbances in the industrial electrical distribution
network caused by nonlinear loads and reactive compensation devices. The study focused on identifying the
magnitude and propagation of harmonic distortion as well as potential resonance conditions that may adversely
affect equipment performance, system efficiency, and protection coordination. All simulations were performed
using ETAP software, employing harmonic load flow and frequency scan techniques in accordance with IEEE
harmonic assessment guidelines [1].
Harmonics Overview
Harmonics are voltage or current components whose frequencies are integer multiples of the fundamental supply
frequency (50 Hz in India). These components are primarily generated by nonlinear loads such as variable
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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frequency drives, rectifiers, and power electronic converters, which draw non-sinusoidal currents even under
sinusoidal voltage conditions.
The presence of harmonics can lead to transformer overheating, increased losses in rotating machines, capacitor
stress, nuisance tripping of protective devices, and possible resonance amplification within the network.
To quantify waveform distortion, Total Harmonic Distortion (THD) is used as defined in IEEE Std. 519 -2014
[1]. The current THD is calculated using (1), while voltage distortion is evaluated using (2). These indices were
computed at multiple buses to identify critical locations where distortion exceeded recommended limits.
To quantify the harmonic content in a waveform, the IEEE 519-2014 standard defines Total Harmonic Distortion
(THD) as follows:
× 100% (1)
Where:
I₁ = RMS value of the fundamental current
I₂, I₃, ..., Iₙ = RMS values of harmonic current components
× 100% (2)
Where:
V₁ = RMS value of the fundamental voltage
V₂, V₃, ..., Vₙ = RMS values of harmonic voltage components
Total Harmonic Distortion (THD) represents the degree of waveform distortion caused by harmonic components
relative to the fundamental frequency. It serves as a key indicator of power quality and is widely used to assess
the impact of nonlinear loads on electrical networks.
In the studied industrial system, multiple VFD-driven loads, including raw mill drives, crusher motors, and
process fans, act as dominant harmonic sources.
These nonlinear devices inject harmonic currents into the distribution network, leading to voltage distortion,
additional losses, and potential resonance interactions with reactive compensation equipment.
A harmonic load flow analysis was therefore carried out using ETAP to evaluate the magnitude and propagation
of harmonic currents and voltages across various buses.
The calculated THD values were compared against the limits recommended by IEEE Std. 519-2014 to identify
critical buses requiring mitigation.
The key objectives of the THD assessment included:
• Measurement of voltage and current THD at major PCC locations
• Identification of buses exceeding IEEE harmonic limits
• Evaluation of harmonic propagation and accumulation within the network
• Supporting the design of passive filtering and resonance mitigation strategies
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Resonance Conditions in Industrial Networks
Resonance in an electrical power system occurs when the effective inductive reactance of the network equals
the capacitive reactance at a specific frequency, resulting in significant amplification of harmonic voltage or
current. In industrial distribution systems incorporating power factor correction capacitors, parallel resonance is
particularly critical because it may cause excessive voltage magnification and overstressing of capacitor banks.
The resonance frequency is determined using (3). If this frequency coincides with dominant harmonic orders
such as the 5th or 7th, severe harmonic amplification, increased equipment losses, and protection maloperation
may occur. Consequently, resonance assessment is essential for ensuring reliable operation of industrial power
systems with nonlinear loads and reactive compensation.
The parallel resonance frequency is expressed as:
(3)
Where:
= Resonant frequency (Hz)
L = Equivalent inductance (H)
C = Capacitance of the capacitor bank (F)
Parallel resonance can lead to several adverse effects, including:
• Overstressing and premature failure of capacitor banks
• Voltage magnification at harmonic frequencies
• Nuisance tripping of protective relays and circuit breakers
• Increased harmonic distortion across the network
In this study, frequency scan analysis was performed at buses containing capacitor banks to identify resonance
peaks using impedance versus frequency characteristics obtained from ETAP. The analysis enabled detection of
critical resonance conditions and supported the selection of appropriate mitigation measures such as detuned
filtering and capacitor bank tuning.
METHODOLOGY
The harmonic study was performed in ETAP using the following structured approach:
1. Model Development: A comprehensive Single Line Diagram (SLD) of the cement plant was created in ETAP,
incorporating all major buses, power transformers, motors, VFD loads, capacitor banks, and the grid connection.
Accurate modeling of impedances, load profiles, and grounding was ensured.
2. Non-linear Load Identification: All significant non-linear loads such as variable frequency drives, converters,
and inverters were identified and modeled with their respective harmonic current spectra based on equipment
datasheets or typical harmonic profiles as per IEEE 519.
3. Harmonic Load Flow Analysis: The Harmonic Load Flow module was used to compute the voltage and current
harmonics across the network. Total Harmonic Distortion (THD) values were evaluated at multiple PCCs and
critical buses to identify locations with excessive distortion.
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4. Frequency Scan Analysis: For buses equipped with capacitor banks, ETAP’s Frequency Scan function was
utilized to sweep the system impedance over a wide frequency range (0 Hz to several kHz). This helped identify
parallel resonance frequencies by detecting peaks in bus impedance.
5. Standard Comparison: All observed harmonic distortion levels were compared against the allowable limits
specified in IEEE 519-2014. This allowed the identification of non-compliant locations requiring corrective
measures.
6. Result Interpretation and Mitigation Planning: Based on the analysis results, causes of observed power quality
issues were correlated with field symptoms reported by plant personnel. Mitigation strategies, including detuned
reactors and passive filters, were proposed and evaluated in ETAP.
RESULTS AND SUGGESTION
Suggestion-01:
At Load Centre-01 bus, located upstream near the transformer, harmonic analysis revealed that the current Total
Harmonic Distortion (THD) exceeded acceptable limits. The measured THD at this location was 22.18%,
significantly higher than the permissible limits defined by IEEE 519 for systems below 69 kV. The excessive
current THD at Load Centre-01 bus is primarily attributed to the presence of multiple VFD-based drives
connected to the crusher and auxiliary motor loads. The relatively low short-circuit strength at the bus (Isc/IL =
24) increases system harmonic sensitivity, resulting in amplified harmonic current distortion and higher thermal
stress on connected cables and transformers.
Further analysis showed that the 5th harmonic was the dominant contributor to the distortion. Additionally, the
harmonic current flowing through the connected cable was beyond its thermal and insulation limits, potentially
leading to overheating, increased losses, and reduced cable lifespan. at Load Centre-01 bus. The impedance
characteristics of the upstream network allowed the 5th harmonic current to propagate toward the transformer,
increasing copper losses and causing additional voltage distortion at adjacent buses. This indicates that the
harmonic problem was not localized but had the potential to affect upstream equipment reliability.
I
SC
= 28000 A
I
L
= 1185 A
So I
SC
/I
L
=24, so the current THD should be less than 8% as per IEEE 519-2014, but it is 22.18%.
Bus ID
Current
THD (%)
Voltage THD
(%)
IEEE 519 Status
Technical Observation
Load Centre-01
22.18
2.96
Severe violation
Dominant 5th harmonic source;
filter installation required
Load Centre-04
1.61
0.685
Within limit
Normal harmonic level
Load Centre-03
1.04
0.575
Within limit
Electrically stable bus
P.H, Kiln & Cooler
Bus
5.95
0.486
Near limit
Moderate VFD harmonic
contribution
Cement Mill HT Bus
3.92
0.458
Within limit
Acceptable distortion
Load Centre-05
0.982
0.239
Within limit
Very low distortion
Load Centre-06
1.15
0.248
Within limit
Stiff bus with minimal harmonic
propagation
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Raw Mill HT Bus
8.07
1.78
Critical
High nonlinear loading; resonance
risk
Load Centre-02
1.73
1.32
Within limit
Slight voltage distortion but
acceptable
Table 1: THD level observed at different buses
The results indicate that harmonic distortion is highly localized, with Load Centre-01 acting as the primary
harmonic injection point within the distribution network. Although voltage THD at Load Centre-01 bus remains
within IEEE-519 limits, the current THD is significantly high due to dominant nonlinear load current injection.
The relatively low voltage distortion indicates a stiff upstream system; however, excessive harmonic current
may still lead to overheating, equipment stress, and potential resonance risk, thereby necessitating harmonic
mitigation.
Mitigation Strategy:
A single-tuned passive filter tuned to the 5th harmonic (250 Hz) was selected due to the clear dominance of the
5th harmonic component and its cost-effective implementation compared to active filtering solutions. The filter
provides a low-impedance path for harmonic currents while simultaneously improving reactive power
compensation at the bus. Passive filtering was preferred over active filtering due to lower installation cost,
reduced maintenance requirements, and predictable harmonic spectrum in cement plant drives.
Figure 1: Harmonics spectrum
5
th
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Figure 2: Harmonics filter sizing
Figure 1 The harmonic spectrum indicates dominance of the 5th harmonic component, which is typical in
industrial systems employing 6-pulse rectifier based variable frequency drives. Characteristic harmonics
generated by such converters follow the order , making the 5th harmonic the lowest and most
significant component.
Additionally, the negative sequence nature of the 5th harmonic contributes to increased motor heating and losses.
The presence of capacitor banks in the network further increases the possibility of parallel resonance near the
5th harmonic frequency, resulting in amplification of distortion at Load Centre-01.
After installing the filter, the current THD at the bus reduced from 22.18% to 6.83%, bringing the harmonic
distortion within acceptable IEEE 519 limits. The post-mitigation results confirm the effectiveness of the filter,
with THD reduced below IEEE 519 recommended limits. Additionally, no adverse resonance amplification was
observed in the impedance scan, validating the stability of the proposed mitigation strategy. This solution has
improved power quality, reduced the thermal stress on cables and transformers, and ensured regulatory
compliance.
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Figure 3: THD level at Load Centre-01 bus before mitigation
Figure 4: THD level at Load Centre-01 bus after mitigation
Bus Location
THD-I Before (%)
THD-I After (%)
IEEE 519 Limit
Compliance
Load Centre-01
22.18
6.83
8%
Achieved
Table 2: THD level at Load Centre 01 bus
Importantly, the addition of the filter did not introduce any new parallel resonance issues. This is because the
system's parallel resonance frequency was located near the 3rd harmonic (~150 Hz), and 3rd harmonic
components are negligible in the system due to the absence of their sources.
Harmonic analysis was also performed at other major buses in the plant. Both current and voltage THD levels
were found to be within the permissible limits specified by IEEE 519-2014. No significant harmonic distortion
or resonance issues were observed at these locations, so no additional mitigation measures were required.
From a practical perspective, passive filters offer lower installation and maintenance costs compared to active
harmonic mitigation techniques, making them suitable for cement industry applications where harmonic sources
are predictable and dominant harmonic orders are well defined.
Suggestion-02:
Parallel Resonance at Load Centre-02 Bus:During the harmonic analysis at Load Centre-02 bus, a parallel
resonance condition was detected due to the connection of a 600 kVAR capacitor bank. The system’s Thevenin
impedance at the bus was calculated using the following formula:
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(4)
Ω
where
= Thevenin equivalent impedance at the bus (Ω)
= line-to-line voltage (V)
= short-circuit current (A)
voltage (V)
= short-circuit current (A)
Figure 5: Parallel Resonance condition
The frequency scan results indicated a resonance peak near the 7th harmonic frequency (≈350 Hz), where the
system impedance increased to approximately 0.057 Ω. The Thevenin impedance at the bus was calculated as
0.0053 Ω, resulting in a resonance amplification factor exceeding 10. According to industrial harmonic
mitigation practices, such impedance magnification indicates a high risk of harmonic voltage amplification even
when THD levels remain within IEEE 519 limits.
The resonance condition was primarily caused by the interaction between the 600 kVAR capacitor bank and the
upstream system inductance. Although measured THD values were acceptable, sustained operation under this
condition could lead to capacitor overstressing, insulation degradation, and possible protection maloperation.
Therefore, frequency scan analysis is essential in addition to THD assessment when capacitor banks are present
in industrial distribution systems.
To mitigate this issue, a detuned reactor was installed in series with the capacitor bank. The original capacitive
reactance was calculated as Xc=0.287 Ω. A 7% detuning factor was selected, resulting in an inductive reactance
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of XL=0.0179 Ω. The addition of this series inductance shifted the resonance frequency from the 7th harmonic
to approximately the 3rd harmonic (≈150 Hz), where harmonic content in the system is negligible.
This detuning strategy successfully eliminated the resonance risk while preserving the reactive power
compensation benefits of the capacitor bank without introducing significant additional losses or cost.
CONCLUSION
This research addressed key power quality issues in an industrial cement plant by conducting a detailed harmonic
analysis using ETAP software. The study focused on identifying and mitigating Total Harmonic Distortion
(THD) and parallel resonance conditions that can adversely affect equipment performance and system stability.
At one major load center, excessive current harmonics were identified and mitigated using a passive filter tuned
to the dominant harmonic frequency. The filter successfully reduced distortion levels and improved overall
power quality without introducing new resonance risks, as the system's resonance frequency remained in a safe
range.
Another critical observation was a parallel resonance condition caused by the interaction of a capacitor bank
with the system impedance. Though THD levels were within limits, the resonance risk was mitigated by detuning
the capacitor bank with a series reactor, effectively shifting the resonance point to a non-problematic harmonic.
Harmonic assessments at other buses showed compliance with IEEE 519 standards, confirming that no further
mitigation was necessary. The results emphasize the value of detailed harmonic studies in identifying hidden
power quality challenges and implementing cost-effective solutions that enhance system reliability and
longevity.
REFERENCES
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