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Power Systems Engineering Thesis

2020

IDENTIFICATION AND CORRECTION

OF POWER QUALITY PROBLEMS

USING DYNAMIC VOLTAGE

RESTORER CASE STUDY:

AMHARA-PLASTIC PIPE FACTORY

ALEMU, GETNET

http://hdl.handle.net/123456789/11696

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Identification and Correction of Power Quality Problems/ July, 2020

BAHIR DAR UNIVERSITY

BAHIR DAR INSTITUTE OF TECHNOLOGY

SCHOOL OF RESEARCH AND POSTGRADUATE STUDIES

FACULTY OF ELECTRICAL AND COMPUTER ENGINEERING

IDENTIFICATION AND CORRECTION OF POWER QUALITY

PROBLEMS USING DYNAMIC VOLTAGE RESTORER

CASE STUDY: AMHARA-PLASTIC PIPE FACTORY

BY

GETNET ALEMU EWUNETIE

ADVISOR: - DR. TASSEW TADIWOSE

BAHIR DAR, ETHIOPIA

July 2020


Electrical Power Engineering Msc. Thesis I


PROBLEMS USING DYNAMIC VOLTAGE RESTORER (DVR)

BY


A thesis submitted to the school of Research and Graduate Studies of Bahir

Dar Institute of Technology, BDU in partial fulfillment of the requirements

for the degree of master in the Power System Engineering in the Faculty of

Electrical and Computer Engineering.

ADVISOR: DR. TASSEW TADIWOSE

BAHIR DAR, ETHIOPIA

July 2020


Electrical Power Engineering Msc. Thesis II


Electrical Power Engineering Msc. Thesis III

©July, 2020



PROBLEMS USING DYNAMIC VOLTAGE RESTORER (DVR)

ALL IGHTS RESERVED


Electrical Power Engineering Msc. Thesis IV


Electrical Power Engineering Msc. Thesis V

Acknowledgments

First, I would like to thank the almighty God for his mercy and grace, which enabled me

to begin and complete successfully this research work.

Secondly, I would like to express my sincere and deepest appreciation to my advisor Dr.

Tassew Tadiwose for his advice, comments, guidance, suggestions and encouragement at

the start of the study up to the final work of this research. He read all the drafts of my thesis

and taught me to be thorough in analyzing problems. His patience and support have enabled

me to achieve my highest potential in both academic and professional work. This has been

an opportunity of a lifetime for which I am truly thankful.

I would like to extend my greatest gratitude to Amhara Plastic Pipe factory workers,

especially electrical department members who gave valuable data and information

throughout the study period.

I am very grateful to my loving and caring parents for their encouragement and everything

they have done for me throughout my academic career as well as their perpetual support

and blessing prayers, specially my father and mother.

Finally, I would also like to thank my classmates, especially Bahir Dar institute of

technology, electrical and computer engineering staffs for their support, Woldia university

for giving this opportunity, to Bahir Dar Institute of Technology (Electrical and computer

engineering faculty), and my friends to all those who have contributed, directly or

indirectly, in accomplishing this research work. throughout the entire time.


Electrical Power Engineering Msc. Thesis VI

Abstract

Electrical energy is one of the simplest used forms of energy and with the betterment of

technology, the dependency on the electrical energy has been increased rapidly. But, the

quality of power is affected by different internal and external factors. Power quality

problem is any power problems manifested in voltage, current, or frequency deviations that

result in failure or missed operation of utility or end user equipment, due to increasing

quantities of non-linear loads in the industries. Nowadays power quality problem is an issue

to the industrial customers. As a result, many of the industries in our country faced with

the problem of power quality, having various causes.

In This research work, power quality problem identifications and mitigation techniques

have been studied in Amhara pipe factory. The study focuses on investigating and

identifying the power quality problems of the industry. The data required for the study is

collected from the industry using power quality analyzer and from recorded data. Based on

the measurement the following data have been recorded, voltage sags which is less than

90% of the rms voltage, voltage unbalance of 3.214% and current distortions of THD value

that reach 44.63%.

The collected data have been analyzed and computer simulations are done using Mat

lab/Simulink model to show the effectiveness of mitigation techniques.

In this thesis dynamic voltage restorer is used to mitigate the problem of voltage unbalance

and the results shows that the device restores the decreased phase voltages to balanced

value. For voltage sag also dynamic voltage restorer is identified as a solution and the

results shows that the device restores the three phases from 190.5V, 195.2V, and 201.2 V,

respectively to 230 V. Single-tuned multi-branch filters that are 5th and 7th harmonic filters

are designed and simulated for the mitigation of harmonic distortion and the filters are

filtered out the harmonics and reduces the THD value from 44.63% to 0.14%.

Key Words: Power quality, power quality problem, APPF, Identification, correction,

MATLAB/Simulink, DVR. IEEE standards.


Electrical Power Engineering Msc. Thesis VII

Table of Content

Declaration .......................................................................................................................... ii

Acknowledgments.............................................................................................................. iv

Abstract .............................................................................................................................. vi

LIST OF FIGURES ............................................................................................................ x

LIST OF TABLES ............................................................................................................. xi

LIST OF ABBREVIATIONS ........................................................................................... xii

CHAPTER ONE ................................................................................................................. 1

1 INTRODUCTION ......................................................................................................... 1

1.1 Background ............................................................................................................. 1

1.2 Statement of The Problem ....................................................................................... 2

1.3 Objectives of The Thesis ......................................................................................... 3

1.3.1 General Objective ............................................................................................. 3

1.3.2 Specific Objectives ........................................................................................... 3

1.4 Significance of The Thesis ...................................................................................... 4

1.5 Scope and Limitations of the Study ........................................................................ 4

1.6 Methodology Used in This Thesis .......................................................................... 5

1.7 Organizations of The Thesis ................................................................................... 8

CHAPTER TWO ................................................................................................................ 9

2 POWER QUALITY PROBLEMS ASSESSMENT ...................................................... 9

2.1 REVIEW OF LITERATURE.................................................................................. 9

2.2 Site Description ..................................................................................................... 13

2.3 Power Quality Problems........................................................................................ 14

2.3.1 Transients........................................................................................................ 15

2.3.1.1 Impulsive Transients ............................................................................... 16

2.3.1.2 Oscillatory Transient ............................................................................... 16

2.3.2 Long-Duration Voltage Variations ................................................................. 17

2.3.2.1 Overvoltage .............................................................................................. 18

2.3.2.2 Under voltage ........................................................................................... 18

2.3.2.3 Sustained Interruptions ............................................................................ 19


Electrical Power Engineering Msc. Thesis VIII

2.3.3 Short-Duration Voltage Variations ................................................................. 19

2.3.3.1 Voltage Sags ............................................................................................ 20

2.3.3.2 Voltage Swells......................................................................................... 20

2.3.3.3 Interruption .............................................................................................. 21

2.3.4 Waveform Distortion ...................................................................................... 22

2.3.5 Flicker ............................................................................................................. 26

2.3.6 Power Frequency Variations .......................................................................... 27

2.3.7 Voltage Unbalance ......................................................................................... 27

2.4 Assessments of Power Quality Problems .............................................................. 28

2.4.1 Measuring Point .............................................................................................. 28

2.4.2 Measurement Results ...................................................................................... 30

2.4.2.1 Transients ................................................................................................. 30

2.4.2.2 Long Duration Voltage Variation ........................................................... 30

2.4.2.2.1 Overvoltage ......................................................................................... 30

2.4.2.2.2 Under voltage ...................................................................................... 31

2.4.2.2.3 Sustained Interruptions ....................................................................... 31

2.4.2.3 Short Duration Voltage Variations .......................................................... 32

2.4.2.3.1 Voltage Sag ......................................................................................... 32

2.4.2.3.2 Voltage Swell ...................................................................................... 33

2.4.2.3.3 Interruptions ........................................................................................ 33

2.4.2.4 Harmonics ............................................................................................... 34

2.4.2.4.1 Sources and Effect of Harmonics ....................................................... 36

2.4.2.5 Power Frequency Variation ..................................................................... 37

2.4.2.6 Voltage Unbalance .................................................................................. 39

2.4.2.6.1 Causes and Effects of Voltage Unbalance in the Industry.................. 41

2.4.2.7 Flicker...................................................................................................... 42

CHAPTER THREE .......................................................................................................... 44

3 THE EXISTING POWER QUALITY PROBLEMS AND MITIGATION

TECHNIQUES ................................................................................................................. 44

3.1 Voltage Sag Mitigation using Dynamic Voltage Restorer .................................... 44

3.1.1 Basic Configuration of DVR .......................................................................... 45

3.1.2 DVR Capacity, Specifications and Measured Values at The Factory. ........... 48

3.1.3 Cost and Payback Period of DVR .................................................................. 49

3.2 Harmonic Mitigations Using Harmonic Filters ..................................................... 50

CHAPTER FOUR ............................................................................................................. 62


Electrical Power Engineering Msc. Thesis IX

4 SIMULATION RESULTS AND DISCUSSIONS ...................................................... 62

4.1 Mitigation of Voltage Unbalance Problem ........................................................... 62

4.2 Mitigation of Voltage Sag ..................................................................................... 65

4.3 Mitigation of Harmonic Distortion ....................................................................... 68

CHAPTER FIVE .............................................................................................................. 71

5 CONCLUSIONS, RECOMMENDATIONS AND SUGGESTIONS ......................... 71

5.1 Conclusions ........................................................................................................... 71

5.2 Recommendations ................................................................................................. 72

5.3 Suggestions for Future Work ................................................................................ 72

Appendixes ....................................................................................................................... 73

Appendix A. Loads and sample interruptions .............................................................. 73

Appendix B. Power quality analyzer and Sample measurement data. .......................... 76

Appendix C. Electrical Simulink models for simulation .......................................... 79

Reference .......................................................................................................................... 82


Electrical Power Engineering Msc. Thesis X

LIST OF FIGURES

Figure 1.1. Basic steps involved in a power quality evaluation ....................................................... 7

Figure 2.1 Two 800KVA & one 1250KVA T/R ........................................................................... 14

Figure 2.2 single line diagram of Amhara plastic pipe factory with respective values ................. 14

Figure 2.3 Impulsive transient ....................................................................................................... 16

Figure 2.4 Oscillatory transient due to back-to-back capacitor switching ..................................... 17

Figure 2.5 Illustration of voltage sag ............................................................................................. 20

Figure 2.6 voltage sag and swell .................................................................................................... 21

Figure 2.7 DC Offset...................................................................................................................... 22

Figure 2.8 Notching ....................................................................................................................... 23

Figure 2.9 Noise ............................................................................................................................. 23

Figure 2.10 Voltage fluctuation ..................................................................................................... 26

Figure 2.11 Frequency Variations .................................................................................................. 27

Figure 2.12 Voltage unbalance ...................................................................................................... 28

Figure 2.13 Single line diagram of distribution center and measuring points ............................... 30

Figure 2.14 Power Frequency Variation ........................................................................................ 39

Figure 2.15 Percentage of Temperature Rise Due to Voltage Unbalance ..................................... 42

Figure 3.1 Location of DVR .......................................................................................................... 45

Figure 3.2 Single-line diagram of DVR connected in series with the feeder................................. 48

Figure 3.3. Insertion of DVR for voltage sag mitigation. .............................................................. 48

Figure 4.1.Voltage wave form when double-line to ground fault is created .................................. 63

Figure 4.2.Injected two-phase voltage by DVR ............................................................................. 63

Figure 4.3. Voltage with DVR when double-line to ground fault created ..................................... 64

Figure 4.4. Voltage wave form when single-line to ground fault is created .................................. 64

Figure 4.5. Voltage with DVR when single-line to ground fault created ...................................... 65

Figure 4.6. Voltage sag without DVR............................................................................................ 66


Electrical Power Engineering Msc. Thesis XI

LIST OF TABLES

Table 2.1 Sample Events for Short and Long Duration Voltage Variations .................................. 31

Table 2.2 Current distortion limits for distribution systems .......................................................... 34

Table 2.3 Voltage distortion limits ................................................................................................ 35

Table 2.4 Total current and voltage harmonic values of each phase ............................................. 36

Table 2.5 Frequency variation measurement results. ..................................................................... 37

Table 2.6 Measurement results of maximum voltage unbalances. ................................................ 39

Table 3.1 measured data of the APPF ............................................................................................ 52

Table 3.2 Evaluating Filter limit as compared with IEEE standard of 5th harmonic values ......... 57

Table 3.3 Evaluating Filter duty limit as compared with IEEE standard of 7th harmonics. .......... 60

Table 3.4 Design parameters of multi-branch harmonic filter ....................................................... 61


Electrical Power Engineering Msc. Thesis XII

LIST OF ABBREVIATIONS

ACDL Alternative Current Drive Load

ANSI American National Standards Institute

APPF Amhara Plastic Pipe Factory

ASD Adjustable speed drives

ATS Automatic Transfer Switch

CFP Compressor Fans and Pups Load

DVR Dynamic Voltage Restorer

EEP Ethiopian Electric Power

EEU Ethiopian Electric Utility

FACTS Flexible Alternative Current transmission systems

FFT Fast Fourier Transform

GTO Gate Turn-off Thyristor

HDPE High Density Poly Ethylene

IEC International Electro Technical Commission

IEEE Institute of Electrical and Electronics Engineers

IGBT Insulated gate Bipolar Transistor

IGCT Integrated Gate Commutated Thyristors


Electrical Power Engineering Msc. Thesis XIII

MATLAB Matrix Laboratory

MOSFET Metal Oxide Semiconductor Field Effect Transistors

NEMA National Electrical Manufacturers Association, USA

PCC Points of Common Coupling

PF Power Factor

PLCs programmable logic controllers

PQ power quality

PSL Pups for Spraying Load

PU per unit

PWM Pulse Width Modulation

RMS Root Mean Square

SCR Silicon-Controlled Rectifiers

SVCS static var compensators

TDD Total Demand Distortion

THD Total Harmonic Distortion

THDI Total Current Harmonic Distortion

THDU Total Voltage Harmonic Distortion

UPVC Unplasticized Poly Vinyl Chloride

VSC Voltage source convertor


Electrical Power Engineering Msc. Thesis XIV

VSD Variable Speed Drives

VSI voltage source invertor

KHz Kilo Hertz

CDVR Cost of dynamic voltage restorer

CVS Cost of voltage sag

NVS Number of voltage sag per year

VPCC Voltage at point of common coupling

T Fundamental Period Time

S Apparent power

MVA Mega Volt Ampere

MS Milliseconds

T(Year) Payback time

KJ Kilo Jules

KV Kilo Volt

KVA Kilo Volt Ampere

KVAR Kilo Volt Ampere Reactive

KW Kilo Watt


Electrical Power Engineering Msc. Thesis 1

CHAPTER ONE

1 INTRODUCTION

1.1 Background

Electrical energy is the most efficient and popular form of energy and the modern society

is highly dependent on the electric power. The quality of power is affected if there is any

deviation in the voltage, current or frequency values at which the power is being supplied.

Typical power quality problems are, especially in industries include harmonics, transients,

short-duration voltage variations, long duration voltage variations, voltage imbalance,

voltage fluctuations, and power frequency variations.[1]

Poor power quality can result in less productivity, lost and corrupt data, damaged

equipment and poor power efficiency. Power Quality is a broad term used to describe the

electrical power Performance.

Power quality problems and solutions of these problems are site dependent, so the power

quality assessment and mitigation techniques must have focused on industry areas that uses

sensitive loads. Non-linear loads like: switch mode power supplies used in both industrial

and commercial computers / microprocessors; variable speed drives (VSD) used in process

control; arcing device like welders and arc furnaces; silicon-controlled rectifiers (SCR)

used in air-conditioners; and basically, any electronic device which draws current in pulses

are termed to be non-linear loads. Now as per the new restructuring of Ethiopian Electric

Power Corporation, the corporation is split in to two companies namely Ethiopian Electric

Utility (EEU) and Ethiopian Electric Power (EEP) to supply sufficient and quality electric

power for the end-user [2].

Now a day, electric utilities, academic and research centers, and other end users of electric

power have been interested to concern about the quality of electric power. This is because

of mainly to high sensitivity of newer-generation load equipment to power quality

variations, the increasing application of harmonic-generating devices in power systems,



increased awareness of end users about power quality issues, sever consequence of a single

fault in interconnected power systems, and given high attention on maximizing efficiency

and system performance. Electricity customers are exposed to power quality disturbances

and hence could suffer from critical financial losses because of these problems. Large

penetration of sensitive loads in industrial and commercial facilities has substantially

increased their susceptibility to power quality disturbances.

In Industries, especially at Amhara plastic pipe factory electric power interruption is

becoming a day to day circumstance. The drop of the voltage at the loads is causing early

failure of equipment, blackening of light bulbs, and decreased efficiency and performance

of machines. This study focused on identification and correction of power quality problems

of Amhara plastic pipe factory [3].

The power distribution system is made up of sub-transmission lines, power transformers,

distribution transformers, low voltage (LV) Lines, etc. Once the voltage has been lowered

at the distribution substation, the electricity flows to industrial, commercial, and residential

centers through the distribution system.

In industries, power quality is a growing concern that requires higher quality service due

to more sensitive electrical and electronic equipment. The effectiveness of a power system

is measured in terms of efficiency, service continuity or reliability, service quality in terms

of voltage profile and stability and power delivery system performance.

This research work is mainly concerned on power quality problems and solutions to the

identified problems in Amhara plastic pipe factory [4].

1.2 Statement of The Problem

The basic function of the power system is to provide an adequate electrical supply to its

customers as economically as possible at optimized level of quality. Electric power

interruption is highly frequent that industrial plants, governmental and non-governmental

organizations, business centers, commercial centers, residences and other electric power

users are facing challenges for the achievement of their goals.



A small power outage has a great economic impact on the industrial consumers. A longer

interruption may harm practically all operations of the factory. Even though utilization of

harmonic generating devices is increasing from day to day, no emphasis is given to the

issue of harmonic distortions.

The motivating factor to work on this thesis is the occurrence of different power quality

problems in the industry. Voltage sags caused by short circuit faults occurred in the

industry power system resulting in failure of the breaker to trip in case of a fault detected

by the protective relays due to prolonged exposure of short circuit currents, the tripping of

controls to the dc drives, programmable logic controllers (PLCs) and the remote I/O units,

for instance, have been found to trip which leads to a partly shut down of production for

hours or even days leading to significant financial losses and reduction of efficiency and

life span of electrical equipments, particularly motors. Voltage unbalance due to the

presence of single-line to ground and double-line to ground faults. Because of increasing

non-linear loads and these non-linear loads injects current harmonics to the power system,

and these injected harmonics are dangerous for the utility and end users.

Different power quality problems with their causes and consequences have been analyzed

and evaluated. The study focused on appropriate mitigation techniques and found solutions

to the identified power quality problems, improving the power quality and profitability of

the industry.

1.3 Objectives of The Thesis

1.3.1 General Objective

The main objective of this research focuses on identifying or assessing electrical power

quality problems in Amhara plastic pipe factory and setting appropriate solutions.

1.3.2 Specific Objectives

The specific objectives of this study are:

Identify the major power quality problems that exists in the factory.



Identify the causes and major impacts of the identified PQ problems,

Compare the level of those disturbances with acceptable values set by IEEE standards,

Designed and simulated voltage sag, voltage unbalance using DVR and harmonic

distortions mitigation techniques by single-tuned filter and made comprising with

IEEE standards.

Draw relevant conclusions and recommendation to the industry for practical

implementation and further work.

1.4 Significance of The Thesis

In this research work, power quality problems are identified and their mitigation techniques

are simulated, so that the significant is clearly observed, advantages and effectiveness of

DVR and single-tuned passive harmonic filter in power quality improvement for voltage

sag, voltage unbalance and current harmonics are studied respectively. If the industry

implements the solutions provided, it protects their equipment from the effect of different

power quality problems that result from system faults, and injection of harmonic currents

which arises from nonlinear loads and increases the efficiency and performance of the

equipment and it saves the money they lost which causes production loss, damage to

sensitive electronic devices and reduction of equipment efficiency. The study may also be

used as a reference for further researchers on similar areas.

1.5 Scope and Limitations of the Study

It is unlikely to go through all the industries that face poor power quality, due to finance,

capacity and time constraint, the study is limited on Amhara plastic pipe factory by

focusing identifying and correcting power quality problems because the factory is more

convenient for this study. It starts with study and investigates the power quality problems

and their impact to the power quality in electrical system.

The research work after identified the problems, only focuses on the major problem parts

to put the solutions. This research is done in modeling of DVR for voltage sag and voltage

unbalance problems and single-tuned passive harmonic filters for harmonic minimization

by MATLAB/Simulink on personal computer simulation only.



1.6 Methodology Used in This Thesis

To achieve the aforementioned objectives, various tasks were performed as stated below:

First for gating brief and reliable information about power quality problems and mitigation

techniques, many published and unpublished works related to this study, are deeply

reviewed and analyzed. As sources of information books, conference papers, articles,

journals, lecture notes and other reading materials were employed.

Due to the nature of the study, it is started by reviewing literatures related to the

identification of power quality problems, causes of those problems, improvement

techniques, and economic impacts of power systems. Recent and important information

and data have been collected from the factory. The total task of data collection is

accomplished through direct measurement, from recorded data, equipment/wiring

specifications, and by asking the personnel who works on the specific area of concern.

The methodological approach of this study is quantitative that described in: -

Number

Percentage,

Graphs and charts etc.

Data have been collected from the load side of service transformer with respective ratings

of 4.45MVA, 15/0.4KV and 5% impedance.

The factory has two sections:

Old distribution system

New distribution system

Generally, the following methodology have been followed to conduct this research work:

Literature review: A number of published ideas about power quality problems,

identifications and mitigation techniques in books, papers, articles, journals and

lecture note materials have been reviewed.

Interview: Made an interview with electrical personnel to obtain detailed information

about power quality problems.



Data collection: The power quality measurement is taken from the secondary of

service transformers of the industry using Power Quality Analyzer/Fluke 43B Which

is a portable device in which it fabricated for measurement. The device can measure

sags/swells, transients, phase-to-neutral true rms voltage on all three phases, single

phase current, total three phase power and single-phase power per, total three phase

power factor and single-phase power factor, reactive and apparent three phase system

power, frequency, voltage and current total harmonic distortions.

Data analysis: The collected data have been analyzed and compared to the IEEE

Standard 1159-1995.

Propose solutions: Appropriate solutions for power quality problems are established

accordingly.

Modeling and Simulation: Using MATLAB/Simulink software modeling and

simulation of power quality problems have been carried out for the modeled networks.

Analysis of the result: Analyzed the results of the simulation obtained from the

simulating software.

Conclusion, recommendation and suggestions for future work: Significant

approaches have made for generalization of the work, recommend for implementation

and suggest the limitations for future work.



Figure 1.1. Basic steps involved in a power quality evaluation



1.7 Organizations of The Thesis

This thesis is organized in five chapters. Those chapters are summarized as follows:

Chapter 1: Discusses the introduction part in which the background, problem statement,

objective, significance of the study, scope of the study and methodology are included.

Chapter 2: Power quality problems assessment:- Presents a literature survey on the work

accomplished on the area of several issues such as power quality problems, modeling

approaches for mitigations, smart approaches among different papers which are done

related research works, site description, the power quality evaluation procedures and

different types of power quality problems categorized by IEEE Standard 519-1995 in

conjunction with their causes and adverse effects on the power system, quality

measurement, and the measurement results are described along with the standard values.

Chapter 3: presents about existing power quality problems and mitigation techniques.

Chapter 4: Presents about simulation results and discussions

Chapter 5: -Presents conclusions, recommendations and suggest for future work.



CHAPTER TWO

2 POWER QUALITY PROBLEMS ASSESSMENT

2.1 REVIEW OF LITERATURE

Power quality is defined as provision of voltages and system design so that user of electric

power can have utilized electric energy from the distribution system successfully, without

interference on interruption. The quality of power is affected if there is any deviation in the

voltage, current or frequency values at which the power is being supplied. IEEE Standard

1159 defines power quality as the concept of powering and grounding sensitive equipment

in a manner that is suitable for the operation of that equipment.

Power quality problems and its solutions are very important to electricity consumers at all

levels of usage. Sensitive equipment and non-linear loads are more common area in both

the industrial, commercial sectors and the domestic environment, voltage sag, voltage

unbalance and current harmonics are big problems in the case study power system. There

are many different methods to mitigate voltage sags and voltage unbalance, but the use of

a custom power device (DVR) is considered to be the most efficient method. DVR is a

Custom Power Device used to eliminate voltage disturbances. The voltage sag and swell

detection are the primary concerns to improve the power quality by dynamic voltage

restorer (DVR), is used to improve power quality more than other FACTS devices due to,

having the ability to control active power flow, having higher energy capacitive and

Smaller in size, it is cost effective [4] [5].

The following researches are some of the works that have done previously on power quality

problems and mitigation techniques.

S. Khalid et.al [2011] [6] Defines about power quality according to IEEE Standard 1159,

power quality is the concept of powering and grounding electronic equipment in a manner

that is suitable to the operation of the equipment and compatible with the premise wiring

system and other connected equipment.



The paper critically discusses about the power quality problems, issues and related

standards, assessment of power quality issues and methods for its correction with giving a

thorough knowledge of harmonics, power quality indices, parameters effecting electric

power. This paper presented an innovative technology management by critical analyzing

about power quality problems, issues, related international standards, and their effect in

life and the corrective measures using different means. The corrective measures are also

discussed which can be remedy for power quality problems generated in different

equipment.

Saurabh Sahu et.al [2018] [7] Explained about power quality problem is an occurrence

manifested as a nonstandard voltage, current or frequency that results in a failure or a miss-

operation of end use equipment. Utility distribution networks, sensitive industrial loads,

and critical commercial operations all suffer from various types of outages and service

interruptions which can cost significant financial 1oss per incident based on process down-

time, lost production, idle work forces, and other factors. Using the two approaches to the

mitigation of power quality problems from customer or from utility side. First approach is

called load conditioning, which ensures that the equipment is less sensitive to power

disturbances, allowing the operation even under significant voltage distortion and the

second is utility conditioning to maintained the supply power. Custom power devices could

be the effective means to overcome some of the major power quality problems by the way

of injecting active or reactive power into the system by modeling of DVR devices.

Dharmendra Gour et.al [2015] [8] Deals that, the origin of events which affect quality of

power is mainly harmonic distortion in addition to voltage sag, swell, and other power

quality disturbances. Different types of filters are studied and used for power quality

improvement by concentrated on eliminating or reducing harmonics. Active power filter

and passive power filter are considered to improve power quality by reducing harmonics.

The high impedance imposed by the series active power filter is created by generating a

voltage of the same frequency that the current harmonic component that needs to be

eliminated. In addition to harmonic current compensation, Passive power filter provides



reactive power compensation, dc bus voltage regulation and enhancing system

performance at large.

Zia Hameed et.al [2016] [9] Harmonic distortion is one of the major issues to maintain

the power quality. From the results shown that harmonics are removed by using active

shunt filters. Harmonics not only effects the power quality but also cut down the useful life

of the power apparatus. Harmonics is all time concern present in the fundamental signal.

Harmonics analysis is also very important to study all the effects. Innovative technology

management by critical analyzing about power quality problems, issues, related

international standards, and their effect in life and the corrective measures using different

means are presented.

Sandesh Jain et.al [2012] [10] Power quality is improved by power factor correction and

harmonic reduction in which voltage source inverter (VSI) is used that injects current in to

the system, which compensates the undesired load current. The filter circuit is incorporated

in to the system design to filter out the harmonics and supply the reactive power without

any interruptions. IEEE 519-1992, Recommended Practices and Requirements for

Harmonic Control in Electric Power Systems, established limits on harmonic currents and

voltages at the point of common coupling (PCC), or point of metering.

Manila Garg et.al [2015] [11] Power quality issues have become important to electricity

consumers at all levels of usage. Sensitive equipment and non-linear loads are now more

commonplace in both the industrial commercial sectors and the domestic environment. The

interest in Power Quality (PQ) is related to all three parties concerned with the power i.e.

utility companies, equipment manufacturers and electric power consumers. The power

quality survey is the first, and perhaps most important step in identifying and solving power

problems cited previously. In other words, it is thus designed to locate, identify and

eliminate the electrical disturbances which disrupt data collection networks. Different

mitigation equipment’s are used to improve power quality problems.



Shweta Gupta et.al [2015] [12] Power Quality related issues are of most concern

nowadays. The widespread use of electronic equipment, such as information technology

equipment, power electronics such as adjustable speed drives (ASD), programmable logic

controllers (PLC), energy-efficient lighting, led to a complete change of electric loads

nature. Due to their non-linearity, all these loads cause disturbances in the voltage

waveform. Several studies have been made to evaluate the costs of PQ problems for

consumers. The assessment of an accurate value is nearly impossible; so, all these studies

are based on estimates. The mitigation of PQ problems may take place at different levels:

transmission, distribution and the end-use equipment.

Ogunboyo Patrick et.al [2018] [13] Describes investigations of poor voltages, causes and

large economic losses are analyzed. provides an investigative study on the typical 11/0.4

kV, low voltage electric power distribution network. The network was modelled with

standard network parameters for low voltage typical electric power distribution network

using MATLAB/Simulink Sim Power System tool box. The summary of the paper gives

recommendations on effective methods for enhancing voltage profile and correcting the

unbalanced voltage to an allowable standard.

Muhammad Rusli et.al [2015] [14] Deals the rise of harmonics in the 20 kV distribution

systems because of non-linear loads supplied by the distribution system. Two types of

harmonics are stated current harmonic distortion and voltage harmonics distortion. The

study discovered current total harmonic distortion that are injected into the 20 kV

distribution system reduced by using a harmonic filter. There are an active filter and passive

filter, with economic considerations passive filter is the best option to reduce the level of

harmonics in the 20 kV distribution system. By changing the power factor of 0.86 to 0.95,

individual harmonic distortion current 5th order can be reduced. Filter capacity needed to

compensate harmonic 5th order of electricity supplier (20 kV).

T.Thomas et.at [2019] [15] Explains about power quality problems and future works, thus

power system or main grid capacity to provide a clean and steady supply of electricity is



known as power quality. Due to strong demand of electronic equipment, the progress of

electric power utilization and rising non- linear loads on electrical system network may

leads to many power quality related issues.

This paper summarizes the various power quality problems such as variation of voltage,

transient, harmonics, sags and swells, interruptions and harmonics. To solve these

problems, the better way is to restore the technology, selection of equipments with less

sensitivity and also the use of the interfacing devices. The considerable power quality

problems are voltage sag, voltage swell, fluctuations of voltage, voltage unbalance,

flickering, harmonic distortions, voltage dips, variations in frequency, very short

interruptions, electrical noise, under voltages, very long interruptions, etc. Harmonics is

one of the major power quality issue and is termed as the integer multiple of fundamental

frequency.

2.2 Site Description

Amhara plastic pipe factory is one of the plastic multifunction manufacturing industry,

which is found in the south west of Bahir Dar town. The factory is established in 2003 to

become one of the top five leading plastic industries in east Africa. To produce and sale

high quality products of Unplasticized Poly Vinyl Chloride (UPVC), High Density Poly

Ethylene (HDPE), and Geo membrane and constantly strive to meet customer needs and

expectations, enhancing its market share all over the region and to be preferred company

in domestic and export markets.

To produce the above products, the factory receives power via 15KV power lines from

Ethiopian electric power (North West region) and stepped down by service transformer to

400V. The power consumption of the factory is 2.85 MVA from two 800KVA & one

1250KVA step down transformers for UPVC, HDPE and Geo membrane sheet machines

and 1.6 MVA from two 800KVA step down transformers for green sheet and recycles

machines. Totally 4.45 MVA power is delivered by north west district EEU from the high

voltage side 15KV main air force distribution line.



Figure 2.1 Two 800KVA & one 1250KVA T/R

15KV

15KV

400V

15/0.4KV

`

T4 T515/0.4KV

15/0.4KV15/0.4KV15/0.4KV

Load-1

Load-2 Load-3

Load-4

Load-5

Load-6

Load-7

Load-8

Load-9

Load-10 Load-11 Load-12

em em

em

New expansion line

Old distribution line

KVAR

400V

T1T2 T3

ATS

Automatic

transfer

switch

DB1

Distribution board 1

DB2

Distribution board

2

Figure 2.2 single line diagram of Amhara plastic pipe factory with respective values

2.3 Power Quality Problems

Power quality problem is any power problems manifested in voltage, current, or frequency

deviations that result in failure or missed operation of utility or end user equipment.



The specific power quality problems that need to be evaluated will be different from

customer to customer. The types of equipment used by the end-user, process requirements

and economic impacts of problems will lead to a list of problems that need to be studied

[1] [4] [6].

According to IEEE Standard 1159-1995, power quality problems classified into seven

major categories described as follows [15] [6].

2.3.1 Transients

The term transient in the analysis of power system is to denote an event that is undesirable

and momentary in nature. This phenomenon is an aperiodic function of time and has a short

duration, is voltage or current surges [16].

Transients can be classified into two categories, impulsive and oscillatory. These terms

reflect the wave shape of a current or voltage transient and there are many causes that

transients can be produced in the power system. Such as:

Arcing between the contacts of the switches

Sudden switching of loads

Poor or loose connections

Lightening strokes

The following listed consequences are there because of Transients [17]:

Electronics devices are affected and show wrong results

Motors run with higher temperature

Failure of ballasts in the fluorescent lights

Reduce the efficiency and lifetime of equipment



2.3.1.1 Impulsive Transients

An impulsive transient is a sudden, non-power frequency change in the steady state

condition of voltage, current or both, that includes unidirectional in polarity.

Impulsive transients are caused by lightning strikes and lightning strokes can occur due to

direct strike to a power line or from magnetic induction or capacitive coupling from strikes

on adjacent lines. Impulsive transients can excite the natural frequency of power system

circuits and produce oscillatory transients.[18]

2.3.1.2 Oscillatory Transient

An oscillatory transient is a sudden, non-power frequency change in the steady-state

condition of voltage, current or both, that includes both positive and negative polarity

values. An oscillatory transient consists of a voltage or current whose instantaneous value

changes polarity rapidly. It is described by its spectral content (predominate frequency),

duration, and magnitude. The spectral content subclasses in to high, medium, and low

frequency and the frequency ranges for these classifications are chosen to coincide with

common types of power system oscillatory transient phenomena.

Figure 2.3 Impulsive transient



Oscillatory transients with a primary frequency component greater than 500 kHz and a

typical duration measured in microseconds (or several cycles of the principal frequency)

are considered high-frequency transients. These transients are often the result of a local

system response to an impulsive transient. A transient with a primary frequency component

between 5 and 500 kHz with duration measured in the tens of microseconds (or several

cycles of the principal frequency) is termed a medium frequency transient. Medium-

frequency transients can also be the result of a system response to an impulsive transient

[19].

A transient with a primary frequency component less than 5 kHz, and a duration from 0.3

to 50 ms, is considered a low frequency transient. This category of phenomena is frequently

encountered on utility sub transmission and distribution systems and is caused by many

types of events; the most frequent is capacitor bank energization [20].

2.3.2 Long-Duration Voltage Variations

Long-duration variations encompass root-mean-square (rms) deviations at power

frequencies for longer than 1 min. ANSI specifies the steady-state voltage tolerances

expected on a power system. A voltage variation is considered long duration when the

ANSI limits are exceeded for greater than 1 min [5].

Figure 2.4 Oscillatory transient due to back-to-back capacitor switching



Long-duration variations can be either overvoltage or under voltages. The causes of these

variations are not the result of system faults, but

Human error

Improper functioning of protective equipment

Load variations in the system

System switching operations

Such variations are typically displayed as plots of rms voltage versus time.

This type of voltage variation leads to the stoppage of power completely for a period of

time until the fault is cleared. The long duration voltage variation may be either of an under

voltage, over voltage or sustained interruption as discussed below [6].

2.3.2.1 Overvoltage

An overvoltage is an increase in the rms ac voltage greater than 110 percent at the power

frequency for duration longer than 1 min. Overvoltage are usually the result of [11]:-

Switching off large load

Energizing a capacitor bank.

The consequences of overvoltage are:

The system is too weak for the desired voltage regulation

Voltage controls are inadequate.

Incorrect tap settings on transformers

2.3.2.2 Under voltage

An under voltage is a decrease in the rms ac voltage to less than 90 percent at the power

frequency for the duration of longer than 1 min [21].

Under voltages is the result of:

Switching on large loads

De-energizing (switching off) a capacitor bank

A cause of under voltage is availability of too much impedance in the power system.

Therefore, the terminal voltage drops too low under heavy load.



Possible effects include

system shutdown

malfunctioning of certain equipment

equipment operation at reduced efficiency

2.3.2.3 Sustained Interruptions

When the supply voltage has been zero for a period of time in excess of 1 min, the long-

duration voltage variation is considered as sustained interruption.

Sustained interruptions can result from control [11] malfunction, faults, or improper

breaker tripping.

2.3.3 Short-Duration Voltage Variations

Short duration voltage variations include root mean square (rms) voltage variations at

power frequencies for a period of less than 1 minute.

The causes of these short duration voltage variations are-

Opening of an Automatic Re-closure

Lightening stroke or Insulation Flash over

Energization of large loads which require high starting currents

Intermittent loose connections in the power wiring.

Consequences:

The data storage system gets affected

There may be malfunction of sensitive devices like- PLC’s, ASD’s.

Based on the type of fault, the short duration voltage variation may be classified into

voltage sag (dip), voltage rise (swell), or interruption [22].



2.3.3.1 Voltage Sags

It is a reduction in voltage outside the normal tolerance for a short time less than few

seconds, that is a decrease to between 0.1 and 0.9 p. u in rms voltage or current at the power

frequency for durations from 0.5 cycle to 1 min [23].

The magnitude of the reduction is between 10 percent and 90 percent of the normal (rms)

voltage [21].

Voltage sags are usually associated with: -

Starting of an electric motor, which draws more current

Faults in the power system

Sudden increase in the load connected to the system

Starting of large motors.

It reduces the energy being delivered to the end user, causes computers to fail, adjustable

speed drive to shut down, and motors to stall and over heat [22].

2.3.3.2 Voltage Swells

A swell is defined as an increase in voltage between 1.1 and 1.8 pu in rms voltage or

current at the power frequency for durations from 0.5 cycle to 1 min [7].

Causes:

De-energization of large load

Figure 2.5 Illustration of voltage sag



Energization of a capacitor bank

Abrupt interruption of current

Change in ground reference on ungrounded phases

Consequences:

Electronic parts get damaged due to over voltage

Insulation breakdown

Overheating

2.3.3.3 Interruption

An interruption occurs when there is a reduction of the supply voltage or load current to

less than 0.1 PU for a duration not exceeding 1 minute. Interruptions are the result of

equipment failures, power system faults and control malfunctions.

The interruptions are measured by their duration since the voltage magnitude is always less

than 10 percent of nominal. The duration of an interruption due to a fault on the utility

system is determined by the operating time of utility protective devices. Delayed reclosing

of the protective device may cause a momentary or temporary interruption. The duration

of an interruption can be irregular when it is due to equipment malfunctions or loose

connections [24].

Figure 2.6 voltage sag and swell



2.3.4 Waveform Distortion

Waveform distortion is a condition whereby a steady-state deviation of the voltage and/or

current waveform from an ideal sine wave of power frequency. There are generally five

types of waveform distortion, namely, dc offset, harmonics, interharmonics [8] notching

and noise.

i. DC Offset

DC offset is the presence of a dc current or voltage in an ac power system. This can occur

due to the effect of half-wave rectification. Direct current (DC) found in alternating current

networks can have a harmful effect. This can cause additional heating and destroy the

transformer.

ii. Interharmonics

Interharmonics are defined as voltages or currents having frequency components that are

not integer multiples of the frequency at which the supply system is designed to operate.

Interharmonics can be found in networks of all voltage classes [25]. The main sources of

interharmonic are cycloconverters, static frequency converters and arcing devices. It is

generally the result of frequency conversion activities and is often not constant; it varies

with load. Such interharmonics currents can excite quite severe resonances on the power

system as the varying interharmonics frequency becomes coincident with natural

frequencies of the system [26].

Figure 2.7 DC Offset



iii. Notching

A periodic voltage disturbance caused by normal operation of power electronic devices

when current is commutated from one phase to another is notching. It tends to occur

continuously and can be characterized through the harmonic spectrum of the affected

voltage.

iv. Noise

Noise is defined as unwanted electrical signals with spectral content lower than 200 kHz

superimposed upon the power system voltage or current in phase conductors. Noise in

power systems can be caused by power electronic devices, control circuits, arcing

equipment, loads with solid-state rectifiers, and switching power supplies. Noise problems

are often exacerbated by improper grounding that fails to conduct noise away from the

power system.

Figure 2.8 Notching

Figure 2.9 Noise



Basically, noise consists of any unwanted distortion of the power signal that cannot be

classified as harmonic distortion or transients. The problem can be mitigated by using

filters, isolation transformers, and line conditioners.

v. Harmonics

Harmonics is a growing problem for both electricity suppliers and users. Harmonic is

defined as a sinusoidal component of a periodic wave or quantity having a frequency that

is an integral multiple of the fundamental frequency usually 50Hz or 60Hz. Distorted

waveforms can be decomposed into a sum of the fundamental frequency and the

harmonics. Harmonic distortion originates in the nonlinear characteristics of devices and

loads on the power system [9].

Harmonics refers to both current and voltage harmonics. Harmonic voltages occur as a

result of current harmonics, which are created by nonlinear electronic loads. These

nonlinear loads will draw a distorted current waveform from the supply system [27]. Loads

like: -

Electric arc furnaces

Discharge lighting (such as fluorescent lamps)

Magnetic cores, such as transformer and rotating machines that require third

harmonic current to excite the iron

Adjustable speed drives used in fans

Blowers, pumps, and process drives can cause harmonic distortion.

The effect of harmonics in the power system includes: -

Corruption and loss of data

Overheating or damage to sensitive equipment

Overloading of capacitor banks.

Using the Fourier series expansion, we can represent a distorted periodic wave shape by its

fundamental and harmonics [28].



( ) ( )

1

( ) sin( ) cos( ) (2.1)DC n s n c

n

U t U U nwt U nwt

The coefficients are obtained as follows:

2

( )0

1( )sin( ) (2.2)n sU u t n t d t

2

( )0

1( )cos( ) (2.3)n cU u t n t d t

2int ,Where nis an eger and T is fundamental period time

T

It is also common to use a single quantity, the total harmonic distortion (THD), as a

measure of the effective value of harmonic distortion. Mathematically, THD values of

voltage and current, THDU and THDI, respectively, are given as follows.

2

( )2

(1)

100 (2.4)nn

u

UTHD x

U

2

( )2

(1)

100 (2.5)nn

I

ITHD x

I

Effective value

2 2

(1)0

1( ) 1 (2.6)

T

RMS UU u t dt U THDT

2 2

(1)0

1( ) 1 (2.7)

T

RMS IU i t dt I THDT

For characterizing harmonic currents in a consistent fashion, [29] IEEE Standard 519-1992

defines another term, the total demand distortion (TDD). This term is the same as the total

harmonic distortion except that the distortion is expressed as a percent of some rated load



current rather than as a percent of the fundamental current magnitude at the instant of

measurement [8].

2

2100 (2.8)

h

h

L

I

TDD xI

Where, 𝐼ℎ is the harmonic currents, 𝐼𝐿 is the rated load-current.

The development of current distortion limit is to:

Reduce the harmonic injection from each single load so that they will not cause

unacceptable voltage distortion levels for normal system characteristics.

Restrict the overall harmonic distortion of the system voltage supplied by the utility.

2.3.5 Flicker

The term flicker is derived from the impact of the voltage fluctuation on lamps such that

they are perceived by the human eye to flicker.

The flicker signal is measured by its rms magnitude expressed as a percent of the

fundamental whereas voltage flicker is measured with respect to the sensitivity of human

eye. It is possible for lamp to flicker if the magnitudes are as low as 0.5% and the

frequencies are in the range of 6 to 8 Hz. One common cause of voltage fluctuations on

utility transmission and distribution system is the arc furnace [30].

Figure 2.10 Voltage fluctuation



2.3.6 Power Frequency Variations

Any deviation of the power system fundamental frequency from its nominal value (usually

50 or 60 Hz) is defined as power frequency variations.

The power system frequency is associated with the rotational speed of the generators

supplying the system. Frequency variations occur as the dynamic balance between load

and generation changes. Frequency variations can be the cause of faults on power

transmission system, large load being disconnected or a large source of generation going

off-line. Frequency variations usually occur for loads that are supplied by a generator

isolated from the utility system. The response to sudden load changes may not be sufficient

to adjust within the narrow bandwidth required by frequency sensitive equipment. Possible

effect could result in data loss, system crashes and equipment [31].

2.3.7 Voltage Unbalance

Voltage unbalance is non-equalization of the three phase voltages. It is a condition in which

the maximum deviation from the average of the three-phase voltages or currents, divided

by the average of the three-phase voltages or currents, expressed in percentage.

The primary source of voltage unbalances of less than 2 percent are: -

Single-phase loads on a three-phase circuit.

Blown fuses in one phase of a three-phase capacitor bank.

Single phasing conditions.

Unidentified single-phase to ground faults

Open circuit on the distribution system primary

Figure 2.11 Frequency Variations



Un stable utility supply

The effects of Voltage unbalance in the electrical systems are: -

Degrades the performance and shortens the life of a three-phase motor.

Phase current unbalance far out of proportion to the voltage unbalance.

currents lead to increased vibrations and mechanical stresses, increased losses,

and motor overheating, which results in a shorter winding insulation life

Unbalanced.

2.4 Assessments of Power Quality Problems

2.4.1 Measuring Point

A general rule, it is necessary to test each location for at least 7 days at the points of

common coupling (PCC) [32]. The electrical power of the factory is supplied to the

installation via two incoming feeders from Bahir Dar substation to keep good reliability.

Each feeder is designed to carry the full load.

The monitoring investigations were performed at the secondary`s of service transformers

for both feeders at different operation conditions. Measurements were carried out with

power quality analyzer instrument on the 400-voltage side for each source separately [33].

Power quality analyzer (Fluke 43B)

Figure 2.12 Voltage unbalance



The power quality measurement is taken from the secondary of service transformers of the

industry using Fluke 43B Power Quality Analyzer.

A “Fluke 43B Power Quality Analyzer” is a portable device utilized for measurement. The

device can measure true rms current per phase, power per phase, power factor per phase,

reactive and apparent three-phase system power, frequency, voltage and current total

harmonic distortion per phase.

Measured Quantities are: -

Transients

Voltage sag (dips) and swell.

Harmonics

Voltage unbalance

Apparent, active and reactive power

Power factor

Frequency deviations

Temperature

Measurements were carried out on the 400-voltage side of the secondary parts of service

transformer for one week and measurements were carried out under different operation

conditions at points of common coupling.



Service Transformers

15,000/400V

400V Bus Bar

Monitoring Location

R S T NR S T

15KV Feeder

pcc

Figure 2.13 Single line diagram of distribution center and measuring points

2.4.2 Measurement Results

The equipment used for power quality measurement is Fluke 430/Fluke 43B Power Quality

Analyzer [3], the detail of the instrument is described in the Appendix. The equipment

measures the following power quality problems:

2.4.2.1 Transients

During the period of monitoring, impulsive transients are not seen because lightning

protection systems are installed at the substation and inside the industry and there is no

oscillatory transient detected by the measurements.

2.4.2.2 Long Duration Voltage Variation

2.4.2.2.1 Overvoltage

During the monitoring period, there is no significant overvoltage in the system.



2.4.2.2.2 Under voltage

Throughout the measurement process, under voltage is not shown even if there is switching

off capacitor bank and switching on off large loads.

2.4.2.2.3 Sustained Interruptions

During the monitoring period frequent interruptions has not occurred which lasted for

longer than 1minute. However, voltage sag events have been found.

Table 2.1 Sample Events for Short and Long Duration Voltage Variations

Events (01/08/2019 - 07/08/2019)

Date Time Type Voltage Levels Duration

L1 L2 L3

01/08/2019 all day normal normal normal normal all day

02/08/2019 11:20:25 Voltage

sag

225 227 224.5 95msec.

03/08/2019 all day normal normal normal normal all day

04/08/2019 19:30:20 Voltage

sag

190.5 195.2 201.2 250msec.

05/08/2019 All day normal normal normal normal All day

06/08/2019 All day Normal Normal Normal Normal All day

07/08/2019 16:30:28 Voltage

sag

224.5 220 219 150msec.



2.4.2.3 Short Duration Voltage Variations

Short-duration voltage variations cover root-mean-square (rms) deviations at power

frequencies for less than 1minute. In order to obtain good measuring data of short duration

voltage variations the measurements are taken at the secondary of the service transformer

for the duration of one week. The voltage variations under this category are mentioned as

follows.

2.4.2.3.1 Voltage Sag

During the measuring process in seven days duration for voltage dips & swells events as

showed in table 3.1, the voltage sag is detected on phase 1,2 and 3 and the voltage decreased

to 225V, 227V and 224.5V for duration of 95msec, 190.5V, 195.2V and 201.2V for

duration of 250msec and 224.5V, 220V, 219V for duration of 150msec and occurred on

the 2nd day at (11:20:25), 4th day at (19:30:20) and 7th day at (16:30:28) respectively. The

problem is caused by three-phase short circuit fault at the electrical system of the industry

and the occurrence of short circuit is recognized when the circuit breakers connected to the

machines trip to clear the fault. The complete data for the voltage sag is obtained from

annually recorded data and interview with the section head.

Therefore, it is necessary to find appropriate mitigation technique.

Effect of Voltage Sag on the Industry: Voltage sags are most occurrence event of all

other power quality disturbances. However, not as costly as interruptions, voltage sags are

much more dominant and, in some cases, may have the same impact as a supply

interruption. Relatively shallow voltage sags can lead to the disruption of manufacturing

processes due to equipment being unable to operate correctly at the reduced voltage levels.

Industrial equipment such as variable speed drives (VSD), PLCs and some control systems

are particularly sensitive to voltage sags. In many manufacturing processes, loss of only a

few vital pieces of equipment may lead to a full shut down of production; leading to

significant financial losses as well as the time taken to clean up and restart the process must

also be considered.



Based on this recorded data when we discuss with the electrical department head of the

industry about the problem, he told me that short circuit faults are frequently occurred in

the industry due to insulation failure of windings, mechanical damage of wires and

improper wiring by technicians resulting in reduction of voltage profile, the problem of

voltage sag measured is an indicator for this event.

Electronic process controls, sensors, computer controls, PLC’s and variable speed drives,

even conventional electrical relays are all to some degree susceptible to voltage sags. In

many cases one or more of these devices may trip if there is a voltage sag to less than 90%

of nominal voltage even if the duration is only for one or two cycles i.e. less than 100

milliseconds. The time to restart production after such an unplanned stoppage can typically

be measured in minutes, hours or even days. Costs per event can be many tens of thousands

of dollars or birr. The resulting effect of voltage sag in the industry is failure of the breaker

to trip in case of a fault detected by the protective relays due to prolonged exposure of short

circuit currents, failure of sensors which check the single strip, the tripping of controls to

the dc drives, and programmable logic controllers (PLCs). It also reduces efficiency and

life span of electrical equipment, particularly motors.

2.4.2.3.2 Voltage Swell

It is an increase in rms voltage or current at the power frequency to between 1.1 and 1.8p.

u for durations from 0.5cycles to 1minute. During the measurement event, the problem of

voltage swell has not detected in any of the three phases.

2.4.2.3.3 Interruptions

An interruption occurs when there is a reduction of the supply voltage or load current to

less than 0.1 p. u for a duration not exceeding 1minute. In APPF, throughout the whole

survey, there has not been short-period interruption detected which lasted for a time

duration of less than one minute. Therefore, in the industry the occurrence of temporary

interruption is rare; as a result, no need to install equipment for mitigation of temporary

interruption.



2.4.2.4 Harmonics

The main industry standard used for harmonics in power systems is IEEE Standard. 519-

1995. This standard has been developed through the IEEE Industry Applications Society

and the IEEE Power Engineering Society. Through the joint effort of these two societies,

IEEE Standards. 519-1995 suggests limits on the harmonic currents that a user can induce

back into the utility power system and also specifies the quality of the voltage that the

utility should supply the user. The table below lists the harmonic current limits based on

the size of the load with respect to the size of the power system to which the load is

connected. The ratio 𝐼𝑆𝐶

𝐼𝐿⁄ is the ratio of the short circuit current available at the PCC

[14] to the maximum fundamental load current. The standard suggests that the amount of

current taken by a facility would have bearing on the number of harmonics; it could

interrupt into the utility’s distribution system. The requirement of the utility to provide a

good quality of voltage is listed in table 2.2 from 120V to 69kV [6].

Table 2.2 Current distortion limits for distribution systems

Maximum harmonic current distortion (% of IL)

Individual harmonic order (Odd harmonics)

ISC/IL h<11 11≤h<17 17≤h<23 23≤h<35 35≤h TDD

<20* 4.0 2.0 1.5 0.6 0.3 5.0

20<50 7.0 3.5 2.5 1.0 0.5 8.0

50<100 10.0 4.5 4.0 1.5 0.7 12.0

100<1000 12.0 5.5 5.0 2.0 1.0 15.0

>1000 15.0 7.0 6.0 2.5 1.4 20.0



Where ISC = maximum short-circuit current at PCC.

𝐼𝐿 Is the maximum demand load-current (fundamental frequency component) at PCC. The

short circuit current and rated current of 400V feeder at the point of common coupling

𝐼𝑆𝐶𝐼𝐿

⁄ ratio is not more than in the range of <20. As a result, the TDD values of the current

harmonics should not exceed 5% at the point of common coupling and the voltage

distortion level limit is shown as in Table 2.3.

Table 2.3 Voltage distortion limits

Bus voltage at PCC

Individual voltage distortion,

TDD (%)

Total Voltage distortion,

THD (%)

69 kV and below 3.0 5.0

69.001kV-161kV 1.5 2.5

161kV and above 1.0 1.5

The maximum voltage and current harmonic contents of the electric power of APPF, when

the industry is working at full load are measured.

The current THD values obtained in the three phases are beyond the permissible range of

the IEEE current distortion limits

The PCC is taken as the secondary side of the transformers serving the industry loads. The

transformer is connected in delta-wye, so that the triplen harmonics (the harmonics that are

multiple of three) cannot enter to the primary side of the transformer that comes from the

load side. Measurements were conducted using Power Quality Analyzer 43B 30-minute

average values were recoded over a period of 1 week in each location. The power quality

analyzer was set to record required data for a period of two weeks in different season.

First data was recorded starting from 19th of April to 25th and the second data was



recorded starting from 1st august to 7th 2019. The average THD of the voltage at the 0.4kV

side ranges between 2.5% and 3.9%. The maximum THD of the voltage is 3.9% while the

minimum values are 2.5%. Therefore, all recorded THD values are below the limits

specified by both IEC and IEEE standards. Summary of the voltage THD in APPF is

presented in Figure form in the appendices. For the current harmonic distortion, the

recorded values of THD at the 0.4 kV ranges between 47.0% and 49.3%. Despite the high

current distortion, the voltage THD is small due to the high short circuit capacity.

It is worth mentioning the dominant harmonic components are [32] the 5th, the 7th, the 11th,

the 13th and the 17th orders. The maximum voltage and current harmonic contents of the

electric power of APPF, when the industry is working at full load are measured and all the

three phase values are summarized in the table below

Table 2.4 Total current and voltage harmonic values of each phase

part VTHD (%) ITHD (%)

R S T R S T

Old distribution

system

2.8% 2.6% 2.9% 49.3%

47.0%

44.63%

New distribution

system

3.3%

3.7%

3.9% 33.5%

30.79%

43.48%

Therefore, it is necessary to install harmonic filters for filtering out the current harmonics

to meet the IEEE standards values.

2.4.2.4.1 Sources and Effect of Harmonics

Harmonic current emissions originate from all types of non-linear loads. Non-linear loads

are loads, which draw non-sinusoidal current and voltage even when the supply voltage is



perfectly sinusoidal. Non-linear loads include saturated magnetic circuits, such as those in

power system transformers and rotating machines, arc furnaces, fluorescent lighting and of

course power electronic loads. Power electronic loads by far are the most significant

harmonic contributors relative to the amount of energy they draw. Specifically, fifth and

seventh harmonics are caused by static power converters used in adjustable speed drives

for motor control, switched mode power supplies and six-pulse static drives. Fifth and

seventh harmonics creates a negative and positive torque, respectively on motors running

from three-phase supply.

Current distortion resulted from non-linear loads have significant adverse effects on both

power system components and customer devices. These effects may result into permanent

damage of the devices. The effects of harmonics in the industry range from false or spurious

operations and trips of fuses and circuit breakers, overheating of transformers due to

increased copper and core losses. The harmful effects of harmonics on transformers often

unnoticed until an actual failure occurs and increased heating in motors due to additional

copper losses and iron losses in the stator winding, rotor circuit and rotor laminations.

2.4.2.5 Power Frequency Variation

The electric power network is designed to operate at a specified value of frequency that is

50Hz for our country. The frequency variations are caused if there is any imbalance in the

supply and demand. Large variations in the frequency are caused due to the failure of a

generator or sudden switching of loads.

Table 2.5 Frequency variation measurement results.



S/No Time (24 Hr. format) Frequency (Hz) Frequency

Variation (Hz)

1 15:05:32 49.98 -0.02

2 05:37:05 50.00 +0.00

3 16:12:14 49.92 -0.08

4 03:55:15 50.1 +0.1

5 10:43:20 50.08 +0.08

6 13:37:26 50.09 +0.09

7 14:10:29 50.13 +0.13

8 16:46:53 49.87 -0.13

9 15:44:18 50.18 +0.18

10 10:31:04 49.94 -0.06

The permissible value of power frequency variations according to the IEEE standard for

normal operation is ±0.5 (49.5Hz to 50.5Hz at 50Hz nominal frequency), which is ±1%.

Based on this standard the measurement result shown above table 2.5 indicates that the

power frequency doesn’t vary much from the permissible limits.

Hence, the power frequency variation is not an issue for the industry and graphical

variations are shown in Figure 2.14.



2.4.2.6 Voltage Unbalance

The unbalance in the voltage is defined as the situation where the magnitudes and phase

angles between the voltage signals of different phases are not equal [13]. The measured

values of maximum voltage unbalances at the industry to compute the percentage of

voltage unbalance at APPF has shown in Table 2.6 below.

Table 2.6 Measurement results of maximum voltage unbalances.

49.7

49.75

49.8

49.85

49.9

49.95

50

50.05

50.1

50.15

50.2

50.25

Freq

uen

cy c

han

ge(H

Z)

Time (hours)

Figure 2.14 Power Frequency Variation



Voltage Measured values in (V)

Phase to neutral voltage V₁ 215.29

V₂ 224.7

Vᴈ 220.25

Phase to phase voltage V₁₋₂ 380

V₁₋ᴈ 396

V₂₋ᴈ 375

According to the NEMA (National Electrical Manufacturers Association of USA) standard

voltage unbalance is defined as the maximum deviation from the average of the three-phase

voltages or currents, divided by the average of the three-phase voltages or currents,

expressed in percentage, which is given by the following equation.

First calculate average value of phase to phase voltages,

1 2 1 3 2 3 (2.9)3

average

V V VV

380 396 375383.67

3averageV

Second, calculate the maximum deviation from the mean

1 2 380 383.67 3.67meanV V

1 3 396 383.67 12.33meanV V



2 3 375 383.67 8.67meanV V

From the above deviations 12.33 is the largest deviation.

arg% *100 (2.10)

mean

L est deviationVoltage unbalance

V

12.33% *100 3.214

383.67Voltage unbalance %

As can be seen from the result the percentage of voltage unbalance is beyond the acceptable

limit imposed by the IEEE limit of 2%, therefore applicable mitigation method should be

implemented.

2.4.2.6.1 Causes and Effects of Voltage Unbalance in the Industry

Causes: Presence of large single-phase loads, faults arising in the system, such as single-

line or double-line to ground fault and the power supplied by the utility.

Consequences:

Presence of harmonics

Reduced efficiency of the system

Increased power losses

Reduce the life time of the equipment

Power loss will increase (𝐼2𝑅 losses) in the rotor and stator, which means more of the

supplied power will be converted to heat in the motor windings due to this, the motor will

run hotter and it breaks down winding insulation, consequently, the motor becomes less

efficient and damaged permanently. The main effects of voltage unbalance are decreased

motor efficiency and performance resulting in motor damage from excessive heat that

affects the company's profitability. Voltage unbalance can create a current unbalance 6 to

10 times the magnitude of voltage unbalance [35].

Here it is clear that the current unbalance can show the existence of current harmonics. The

percent of winding heat increase, expressed in degree Celsius, due to a voltage unbalance



is exponential, and approximately increases by twice the square of the percent of voltage

unbalance. Mathematically,

2% 2*( ) (2.11)of temprature rise voltage unbalance

The percentage of voltage unbalance obtained in the industry using the measured data is

3.214%.

Therefore, the percentage of temperature rise will be:-

2 0% 2 (3.214 ) 20.67of tempraturerise x c

The result of the voltage unbalance of 3.214% is a motor winding running 20.67 hotter

than normal temperature. As percentage of voltage un balance increased then motor

temperature is also increased.

Figure 2.15 Percentage of Temperature Rise Due to Voltage Unbalance

Resistive loads are relatively unaffected by voltage unbalance, but it causes additional

heating/losses with three-phase motors. Variable speed drives (VSD) trip off due to an

increase in AC line currents caused by a compensation for the voltage unbalance [36].

2.4.2.7 Flicker

Voltage fluctuations can cause light intensity fluctuations that can be perceived by our

brains. This effect, popularly known as flicker, can cause great physiological discomfort.



More precisely, flicker is the impression of unevenness of visual sensation induced by a

light motivation whose luminance or spectral distribution properly fluctuates with time.

Through the one-week investigation, the flicker has not occurred and seen in necked eye.

Thus, it is not measured, because it is not an issue for the industry.



CHAPTER THREE

3 THE EXISTING POWER QUALITY PROBLEMS AND MITIGATION

TECHNIQUES

3.1 Voltage Sag Mitigation using Dynamic Voltage Restorer

Among the power quality problems (sags, swells, harmonics…) voltage sags are the most

severe disturbances. In order to overcome these problems, the concept of custom power

devices is introduced recently. One of those devices is the [34] Dynamic Voltage Restorer

(DVR), which is the most efficient and effective modern custom power device. The

function of the DVR will inject the missing voltage in order to regulate the load voltage

from any disturbance due to immediate distortion of source voltage.

A dynamic voltage restorer (DVR) is a solid-state inverter based on injection of voltage in

series with a power distribution system. The DC side of DVR is connected to an energy

source or an energy storage device, while its ac side is connected to the distribution feeder

by a three-phase inter facing injection transformer. A single line diagram of a DVR

connected power distribution system is shown in the figure (1). Since DVR is a series,

connected device, the source current, is same as load current. DVR injected voltage in

series with line such that the load voltage is maintained at sinusoidal nominal value. It is

normally installed in a distribution system between the supply and the critical load feeder

at the point of common coupling (PCC). Other than voltage, sags and swells compensation,

DVR can add other features like line voltage harmonics compensation, reduction of

transients in voltage and fault current limitations [35].



Load1

DVRSensitive

Load

Step down transformerAC Source

Figure 3.1 Location of DVR

3.1.1 Basic Configuration of DVR

The general configuration of the DVR consists of [36]:

A. An Injection/ Booster transformer/Isolation transformer

B. A Harmonic filter

C. Storage Devices

D. Voltage Source Converter/Inverter (VSC/VSI)

A. Injection/ Booster transformer/Isolation transformer

The Injection / Booster transformer is a specially designed transformer that attempts to

limit the coupling of noise and transient energy from the primary side to the secondary

side. In a three-phase system, either three single-phase transformer units or one three-phase

transformer unit can be used for voltage injection purpose.

The injection transformer comprises of two side voltages namely the high voltage side and

low voltage side. The basic function of the injection transformer is to increase the voltage

supplied by the filtered VSI output to the desired level while isolating the DVR circuit from

the distribution network. The transformer-winding ratio is pre-determined according to the

voltage required in the secondary side of the transformer (generally this is kept equal to the



supply voltage to allow the DVR to compensate for full voltage sag. A higher transformer-

winding ratio will increase the primary side current, which will adversely affect the

performance of the power electronic devices connected in the VSI. To evaluate the

performance of the DVR the rating of the injection transformer is an important factor that

need to be considered due to the compensation ability of the DVR is totally depend on its

rating. The DVR performance is totally depending on the rating of the injection

transformer, since it limits the maximum compensation ability of the DVR [8].

B. Harmonic filter [10].

The harmonic filters can be placed either on the high voltage side or the converter side of

the injection transformers. Filter unit consists of inductor (L) and capacitor (C). In DVR,

filters are used to convert the inverted PWM waveform into a sinusoidal waveform. This

can be achieved by eliminating the unwanted harmonic components generated by the VSI

action. Higher orders harmonic components distort the compensated output voltage. The

unnecessary switching harmonics generated by the VSI must be removed from the injected

voltage waveform in order to maintain an acceptable Total Harmonics Distortion (THD)

level.

C. Storage Devices

This is required to provide active power to the load during deep voltage sags. Lead-acid

batteries, flywheel or SMES can be used for energy storage. It is also possible to provide

the required power on the DC side of the VSI by an auxiliary bridge converter that is fed

from an auxiliary AC supply. The DVR need real power for compensation purpose during

voltage disturbance in the distribution system. In this case, the real power of the DVR must

be supplied by energy storage when the voltage disturbance occurs. The energy storage

such as battery is responsible to supply an energy source in D.C form.

D. Voltage Source Converter (VSC)/VSI

A VSC is a power electronic system consists of a storage device and switching devices,

which can generate a sinusoidal voltage at any required frequency, magnitude, and phase

angle. In the DVR application, the VSC is used to temporarily replace the supply voltage

or to generate the part of the supply voltage, which is missing. This could be a 3 phase - 3



wires VSC or 3 phases - 4 wires VSC. The latter permits the injection of zero-sequence

voltages. Either a conventional two-level converter (Graetz Bridge) or a three-level

converter is used. There are four main types of switching devices: Metal Oxide

Semiconductor Field Effect Transistors (MOSFET), Gate Turn-Off thyristors (GTO),

Insulated Gate Bipolar Transistors (IGBT), and Integrated Gate Commutated Thyristors

(IGCT).

E. control and Protection system

The aim of the control system is to maintain voltage magnitude at the point where a

sensitive load is connected, under system disturbances. The harmonics is generated in the

load terminals using six pulse converters with fixed firing angle are connected to the main

drive nonlinear load which is parallel to the sensitive load. Voltage sag is created at load

terminals via a three-phase fault. The above voltage problems are sensed separately and

passed through the sequence analyzer. The control system of the general configuration

typically consists of a voltage correction method which determines the reference voltage

that should be injected by DVR.

The basic functions of a controller in a DVR are the following

a) Detection of voltage sag/swell events in the system

b) Computation of the correcting voltage

c) Generating of trigger pulses to the sinusoidal PWM based DC-AC inverter.

d) Correction of any anomalous (abnormality) in the series voltage injection.

e) Termination of the trigger pulses when the system has passed



AC Voltage SourceSupply

Load1

Load2

Energy Storage Filter

Inverter

Sensitive Load

Injection Transformer

Source Impedance

Line Impedance

Step Down Transformer

DV

R

Figure 3.2 Single-line diagram of DVR connected in series with the feeder

DVRSensitive

Load

PCC (0.4KV)

Figure 3.3. Insertion of DVR for voltage sag mitigation.

3.1.2 DVR Capacity, Specifications and Measured Values at The Factory.

Referring to the electrical system of Amhara plastic pipe factory and measured values,

0.4ppcV kv

1250 , 0.98S KVA PF

75%.Maximumthree phase voltage sag response



250 .Duration sag to protect ms

?KVACapacity of DVR

Re ( ) ?quired energy for DVR KJ

It is recommended to adopt DVR technology to compensate the [21] bus voltage sag and

restore to 100 % of the rated value. When the sag depth is lower than 75 %, therefore, the

compensating voltage of DVR should be 80 % or 0.8 PU.

By taking into consideration of peak load 1250 KVA with power factor of 0.98

0.8 1250 1000Thecompensation power x KVA KVA

Energy Power xTime

The duration of sag to protect is 250 msec. so,

( )The required energy KVA x PF xTime

3(1000 0.98) 250 10E x x x

245E KJ

For more reliability and availability DVR with (1100 KVA, 300 kJ) is selected. And it

should be installed in the 15-kV side of the system.

3.1.3 Cost and Payback Period of DVR

This section describes the cost and benefit analysis of installing DVR to mitigate voltage

sag.

cos DVRAssume t of DVR C

os sin VSC t of gle voltage sag C

VSNumber of sags per year N

( )payback period T year

Then,

DVR VS VSC C x N xT

$300 $300Cos 5%( )t of DVR

KVA KVA [operation and maintenance annual cost]



$315

DVRCKVA

$315

1100DVRC X KVAKVA

$346500DVRC

The cost of voltage sag, VSC at APPF is ($1,500/year), and by taking the average number

of voltage sag occurrence, VSN is 40/year [36].

Then, the payback period will be

DVR

VS VS

CT

C x N

$346500

$1500 40 /T

x year

5.775 6T year years

Since the average life time of the DVR is about 15 years, so the solution is very

economical and feasible.

3.2 Harmonic Mitigations Using Harmonic Filters

The harmonics distortion levels can be reduced through prevention by choosing equipment

and installation practices that minimize the level of harmonics in the system. Various

harmonic-mitigation techniques have been proposed and applied in recent years. In this

case, filters are designed for the distortions that exceed harmonic limits set by the IEEE

Standard519-1992.There are two types of filters used for filtering the harmonic distortions:

passive filters and active filters [8].

1. Passive filter

Passive filters contain inductance, capacitance, and resistance elements configured and

tuned to control harmonics. They are commonly used and are relatively inexpensive



compared with other means for eliminating harmonic distortion. They are employed either

to shunt the harmonic currents off the line or to block their flow between parts of the system

by tuning the elements to create a resonance at a selected frequency [28].

The most common type of passive filter is single-tuned notch filter which is the most

economical and frequently used. In the single-tuned filter circuit, a capacitor and inductor

are connected in series. This filter is also known as low pass filter. The filter is single-tuned

to present low impedance to a particular harmonic current. It is connected in shunt with the

power system there by diverting the harmonic currents from their normal flow path on the

line into the filter.

Notch filter can provide power factor correction in addition to harmonic suppression. The

first order high-pass filter, is not normally used, as it requires a large capacitor and has

excessive loss at fundamental frequency. The second order high-pass filter provides the

best filtering performance, but has higher fundamental frequency losses as compared with

the third order. The third order high-pass filter's [23] main advantage over second order is

a substantial reduction in fundamental frequency loss, owing to increased impedance at

that frequency caused by the presence of additional capacitor.

2. Active Filters

Active filters are relatively new types of devices for eliminating harmonics. They are based

on sophisticated power electronics and are much more expensive than passive filters. They

are designed to inject harmonic currents to counterbalance existing harmonic components

as they show up in the distribution system [37]. However, they have distinct advantage that

they do not resonate with the system. They can address more than one harmonic at a time

and combat other power quality problems such as flicker. They are particularly useful for

large, distorting loads from relatively weak points on the power system. Most of the time

active filters are used in very difficult situations when passive filters can`t operate

successfully because of the parallel resonance lies. Passive filters are more effective for

power system harmonic mitigation than active filters because it is less expensive [38].

3. Design of Multi-Branch Single-Tuned Filter



This section illustrates a procedure for designing harmonic filters for industrial

applications. Passive filters always provide reactive compensation to a degree dictated by

the volt-ampere size and voltage of the capacitor bank used, they can in fact be designed

for the dual purpose of providing the filtering action and compensating power factor to the

desired level. These passive filters present very low impedance, with respect to line

impedance, at the tuning frequency, through which all current of that particular frequency

will be diverted.

Despite its reactive power compensation advantage, a single tuned shunt filter can only

eliminate a single current harmonic component. Therefore, a wide range generated

harmonic a single tuned filter is to be designed for each current harmonic to be suppressed

individually. This means multiple single-tuned filters are designed to eliminate multiple

harmonics [14]. The filter will be designed for 5th and 7th harmonics because these are the

dominant harmonic frequencies in the plant. Therefore, multiple-branch single tuned

harmonic filter is going to be designed. The harmonic filter designed according to the

appropriate equations.

A single tune filter will be designed to mitigate the fifth and seventh harmonic components.

The filter will be tuned slightly below 5th to allow for tolerances in the filter components

and variation in system impedance for fifth harmonic and the filter will be tuned below 7th

to allow for tolerance the filter components and variation in system impedance for seventh

harmonic. Furthermore, it minimizes the possibility of dangerous harmonic resonance in

case the parameters of system change and cause the tuning frequency to shift.

The recorded data of the power and power factor are given in table 3.1.

Table 3.1 measured data of the APPF



Measured Data

S, KVA 709.73

P, KW 580.56

Q, KVAR 408.24

PF 0.86

As can be seen from the above table, the current power factor obtained is 0.86 and it is

required to improve this value around 0.98. The harmonic level of 5th and 7th are high and

should be eliminated.

Steps to determine the capacity of harmonic filters with single-tuned filters at 0.4 kV

bar.

Determine effective power capacity of filter reactive power.

The filter will provide reactive power to the system as a result the capacitor size should be

selected such that it will not cause overvoltage during the light load condition. The power

factor of the system should be improved from 0.86 to 0.98 lagging.

1 1

1 2Re (sin(cos ( ) sin(cos ( ))) 3.1quried Compensation fromthe filter S

1 1709.73(sin(cos (0.86)) sin(cos (0.98))) 220.936effQ KVAR

Where Qeff = reactive power to be compensated

Determination of harmonic duty requirements

The harmonic current that flow through the filter has two components: harmonic current

from utility and harmonic current produced by the nonlinear load.

The nonlinear load produces 18% of fifth harmonic and 13% of seventh harmonics of the

fundamental current [37],



thus

( )( ) (3.2)

3 ( )h h

Rating KVAI I pu

x systemvoltage KV

5 5

( )( ) (3.3)

3 ( )

Rating KVAI I pu

x systemvoltage KV

7 7

( )( ) (3.4)

3 ( )

Rating MVAI I pu

x systemvoltage KV

5

709.730.18 184.393

3 0.4

KVAI A

x KV

7

709.730.13 133.173

3 0.4

KVAI A

x KV

The reactive power is distributed among 5th and 7th harmonic filters as follows:

2 3

, 2,3,... (3.5)...

hfh eff

IQ Q h

I I

5

5

5 7

(3.6)f eff

IQ Q

I I

5

184.393220.936 128.285

184.393 133.173f

AQ KVAR KVAR

A A

7

7

7 5

(3.7)f eff

IQ Q

I I

7

133.173220.936 92.651

133.173 184.393f

AQ KVAR KVAR

A A

Determine the frequency tuning filters

In accordance with IEEE 1531-1993, harmonic single tuned filter frequency is

determined in amount of 3%- 15% [37] below the determined frequency as safety factor.



A. For 5th Harmonics

In this case, use tuning filter frequency of 6% (4.7)

Voltage across the capacitor

2

2( ) (3.8)

1

sc system

s

hV V

h

2

2

4.7( ) 400 418.9664.7 1

cV v v

The rate or standard voltage near this value is 480v.

The reactive power to be supplied by the capacitor is calculated as

5

2

2( ) (3.9)

1

sc f

s

hQ Q

h

2

2

4.7( )128.285 134.3144.7 1

cQ KVAR KVAR

The rated value near to this calculated value is 150kvar

Then,

2

(3.10)c ratedc

c rated

VX

Q

2(480)1.536

150 varcX

k

Reactors



2( ) (3.11)c

L

s

XX

h

2

1.536( ) 0.069

4.7LX

RMS and peak value calculations

Let

1 1.536c cX X

1 0.069L LX X

then

5

1 1.5360.327

4.7

cc

s

XX

h

5 14.7 0.069 0.324L s LX h x X x

Determine RMS current value

2 2

1 (3.12)rms C chI I I

1

1 1

3( ) (3.13)

L L

c

c L

V

IX X

1

400

3( ) 157.4231.536 0.069

c

v

I A

2 2157.423 184.393 242.452RMSI A

Determine peak and RMS voltage

12( ) (3.14)c peak c chV V V

1 1 1 (3.15)c c cV X x I



5(3.16)

hc ch cV X x I

50.327 184.393 60.295cV x v

2(241.802 60.297 ) 427.233peakcV v v v

2 2

1 (3.17)RMSc c chV V V

2 2241.802 60.297 249.207RMScV v

, ,var 3 3 , , ( ) (3.18)cap total RMS total Lk x I x kv cap RMS total

,var 3 242.452 3 0.249207 181.262 varcap totalk x x x k

Rated current

var 150 var180.422

3 0.480

ratedrated

L Lrated

k kI

kv x

Checking either the designed values are within the IEEE 18 recommended limits or not

for the 5th harmonics

,var 181.2620 varvar [ ] 121%

var 150 var

cap total

rated

k kk

k k

, 3 427.233[ ] [ ] 109%

2 480

L cap peak

rated peak

v x vpeak voltage

v x v

242.452[ ] [ ] 134%

180.422

RMS total

rated

IRMS current

I

( ) 3 249.207[ ] [ ] 90%

480

Lcap RMS total

rated

V xRMS Voltage

V

Table 3.2 Evaluating Filter limit as compared with IEEE standard of 5th harmonic values

Duties Definition Limits, % Actual values, %



Peak voltage ( )L cap peak

rated

V

kv

120 109

RMS voltage ( , )L cap total rms

rated

V

kv

110 90

RMS Current ,

,

rms total

cap rated

I

I

135 134

kvar

,

var

var

cap total

cap rated

k

k

135 121

Therefore, all the designed values are within the IEEE 18 recommended limits for the 5th

harmonics.

Now calculate the capacitance and inductance values for the 5th harmonics

Capacitance and inductance values

1 10.0021

2 2 50 1.536c

C FfX x Hz x

0.0690.00022

2 2 50

LXL H

f x Hz

B. For 7th Harmonics

Voltage across the capacitor

In this case, use tuning filter frequency of 6% (6.58)

2 2

2 2

6.58( ) ( ) 480 409.457

1 6.58 1

sc system

s

hV V x v v

h

The rated value near to this calculated value is 480v.

The reactive power is given by

7

2 2

2 2

6.58( ) ( ) 92.651 var 94.875 var

1 6.58 1

sc f

s

hQ Q x k k

h



The standard near value is 100 vark , then cX is determined by

2 20.482.304

100 var

C ratedc

c rated

VX

Q k

The reactor sizes

1

2 2

2.3040.0532

6.58

cL

s

XX

h

RMS current calculations

Let

1 2.304c cX X

1 0.0532L LX X

Then,

7

1 2.3040.35

6.58

cc

s

XX

h

And

7 1 6.58 0.0532 0.350L s LX h x X x

2 2

1RMS c chI I I

1

1 1

400

3 3102.604

2.304 0.0532

L L

c

c L

V V

IX X

2 2102.604 133.173 168.115rmsI



RMS and peak voltage

12( )c peak c chV V V

1 1 1 2.304 102.604 236.399c c cV X x I x v

7 7 70.35 133.173 46.611c c cV X x I x v

2(236.399 46.611 ) 400.237peakcV v v v

2 2

1rms c chV V V

2 2(236.399 ) (46.611 ) 240.950rmsV v v v

, , ( , )var 3cap total rms total L Lcap rms totalk x I x KV

,var 3 168.115 3 0.240950 121.522 varcap totalk x x x k

The near rated value is 105 vark ,then

var 105 var126.295

3 0.48

ratedcap rated

cap rated

k kI

kv x v

Checking either the designed values are within the IEEE standard limits or not for the 7th

harmonics

,var 121.522 var

var [ ] 116%var 105 var

cap total

rated

k kk

k k

, 3 400.237[ ] [ ] 102%

2 480

L cap peak

rated peak

v x vpeak voltage

v x v

168.115

[ ] [ ] 133%126.295

RMS total

rated

IRMS current

I

( ) 3 240.950[ ] 87%

480

Lcap RMS total

rated

V x vRMS Voltage

V v

Table 3.3 Evaluating Filter duty limit as compared with IEEE standard of 7th harmonics.



Therefore, all the designed values are within the IEEE 18 recommended limits.

Now calculate the capacitance and inductance values for the 7th harmonics

Capacitance and inductance values

2.304cX and 0.0532LX ,then

1 10.0014

2 2 50 2.304c

C FfX x Hz x

0.05320.0001693

2 2 50

LXL H

f x Hz

Table 3.4 Design parameters of multi-branch harmonic filter

Branch , varcQ k ,cV V ,cX ,C F ,LX ,L mH

5th 150 480 1.536 0.0021 0.069 0.22

7th 105 480 2.304 0.0014 0.0532 0.169

The cost of fully automatic system is 640 birr/ vark , in the case study, the ratings are 150

and 105 vark for 5th and 7th harmonic filter respectively.

Then, the cost of filter can be calculated as,

Duties Definition Limits, % Actual values, %

Peak voltage ( )L cap peak

rated

V

kv

120 102

RMS voltage ( , )L cap total rms

rated

V

kv

110 87

RMS Current ,

,

rms total

cap rated

I

I

135 133

kvar ,

var

var

cap total

cap rated

k

k

135 116



Cost of filter 640

[150 105] var 163200var

birrk x birr

k

Due to the effect of harmonics on the factory cause miss operations and trips of fuses and

circuit breakers which leads to the damage of equipment and stops production process and

also overheating of transformers and motors resulting in minimizing efficiency and failure

of winding insulation causing short circuit and damage the machines permanently.

Therefore, the solution is very economical as compared to the effect of harmonics on

electrical equipments and it improves the productivity of the factory.

CHAPTER FOUR

4 SIMULATION RESULTS AND DISCUSSIONS

4.1 Mitigation of Voltage Unbalance Problem

As the investigation discovered the presence of voltage unbalance due to the occurrence of

single-line to ground or double-line to ground fault, then the solution for voltage unbalance

problem is modeled and simulated using Mat lab/Simulink software. Voltage wave forms

when double-line to ground fault happened as it has been shown from the figure 4.1



simulation result, the voltage has been decreased from the normal value in the two phases,

so the voltage became unbalanced.

This voltage unbalance is needed to be compensated to get the desired voltage level at the

load side as explained before.

Figure 4.1.Voltage wave form when double-line to ground fault is created

Figure 4.2.Injected two-phase voltage by DVR



When the proposed dynamic voltage restorer (DVR) is in operation, it injects the

appropriate amount of voltage that compensates the missed voltages during double-line to

ground fault. Therefore, the wave form is improved to the normal value and the system is

balanced.

Voltage wave forms when single-line to ground fault happened as it has been shown from

the figure 4.4 simulation result, the voltage has been decreased from the normal value in

one phase, so the voltage became unbalanced. This voltage unbalance is needed to be

compensated to get the desired voltage level at the load side.

Figure 4.3. Voltage with DVR when double-line to ground fault created

Figure 4.4. Voltage wave form when single-line to ground fault is created



During single-line to ground fault the voltage becomes unbalanced, so during this period

the DVR injects the voltage in order to compensate the voltage unbalance problem of on

the faulted phase. When the proposed dynamic voltage restorer (DVR) is in operation, it

injects the appropriate amount of voltage that compensates the missed voltages during

single-line to ground fault. Therefore, the wave forms are improved to the normal value

and the system is balanced.

4.2 Mitigation of Voltage Sag

The appropriate solution for the existing voltage sag problem is modeled and simulated

using MATLAB/Simulink software. The first simulation shows voltage sag problem

without DVR when there is a three-phase short circuit fault in the system at a point with

fault resistance of 1.5 Ω for time duration of 250ms.

This voltage sag is needed to be compensated to get the desired voltage level at the load

side.

Figure 4.5. Voltage with DVR when single-line to ground fault created



To mitigate voltage sag, the simulation is carried out by inserting DVR in the power system

on the load side to compensate the voltage sag occurred due to the three-phase short circuit

fault. The proposed dynamic voltage restorer responds to this sag and injects the

appropriate amount of missed voltage during the sag event for compensation. When the

DVR is in operation the voltage sag is compensated and the rms voltage at the load point

is maintained to the standard voltage level.

Figure 4.6. Voltage sag without DVR



It is clearly observed that the voltage waveform that is obtained after connection of DVR,

the voltage restores for the three phases from the decreased voltage value to 230V. This

shows that the installed DVR is working efficiently

Figure 4.7 Inserted voltage by DVR

Figure 4.8 Voltage sag with DVR



4.3 Mitigation of Harmonic Distortion

The solutions for current harmonic distortion have been simulated using

MATLAB/Simulink software. The designed two branch harmonic filters (5th and 7th) are

simulated effectively that reduced the distortion levels to acceptable values. The current

waveforms presented with and without filtering for comparison.

Figure 4.9 Current waveform without filter

Figure 4.10 FFT analysis of the harmonic currents without filter



The distorted waveform in figure 4.9 and in figure 4.10 from the Fast Fourier Transform

(FFT) analysis the THD value is 44.63%, which is above the IEEE acceptable limit.

Therefore, to compensate the problem, harmonic filters are used; consequently, the

resulting waveform will be purely sinusoidal.

Figure 4.11. Current waveform with filter



The results indicated that single tuned filter has significantly reduced the harmonic currents

that appear at the secondary terminal of the transformer. The current THD level is reduced

from 44.63 % to 0.14 %, and signal is purely sinusoidal due to the compensation provided

by the multi-branch harmonic filter. It is clear that the filters effectively reduce the

distortion level to the acceptable magnitude, i.e. less than 5 %.

Figure 4.12. FFT analysis of the harmonic currents with filter



CHAPTER FIVE

5 CONCLUSIONS, RECOMMENDATIONS AND SUGGESTIONS

5.1 Conclusions

This work presents the assessment of power quality problems and mitigation techniques at

Amhara plastic pipe factory. The assessments have done from recorded data and by fluke

43B direct measurement and the analysis of the recorded data at the point of common

coupling has done based on IEEE standards. The analysis of the recorded data yields,

voltage unbalance, voltage sags and current harmonic distortions are the most severe

events, appropriate mitigation techniques are taken accordingly, and the main conclusions

are drawn as follows.

During the analyses from the collected data that the voltage unbalance percentage has

become 3.214%, so according to institute of electrical and electronics engineering (IEEE)

the standard of voltage unbalance range should not be more than 2%. The voltage

unbalance is caused by single-phase to ground fault or double-line to ground fault

occurrence inside the factory. The effect of voltage unbalance is decreased motor efficiency

and performance resulting in motor damage from excessive heat which affects the

company's profitability. So, this problem had been mitigated by using dynamic voltage

restorer (DVR) facts device effectively.

During the analyses from the collected data, voltage sag, was occurred on the three phases

and the percentage voltage reduction are 17.2% and the voltage decreases to 190.5V, 15.1%

and the voltage decreases to 195.2V, 12.3% and the voltage decreases to 201.2V for

duration of 250 msec. caused by three phase short circuit fault resulting in tripping of

protective device. It has also caused equipment malfunctions and ultimately equipment

damage, particularly motors. So, in order to overcome this problem dynamic voltage

restorer is installed in a distribution system between the supply and the critical load feeder

at the PCC, to restore the voltage to the normal standard voltage level, i.e. 230 V.



In the factory during the assessment period, a distorted current of up to 44.% THD at its

full load is recorded, which is beyond the IEEE current distortion limits. Harmonic current

is originated from non-linear loads, loads which draw non-sinusoidal current, 5th and 7th

harmonics are the dominant harmonic frequencies caused by static power converters used

in adjustable speed drives for motor control, switched mode power supplies and six-pulse

static drives and the negative effects was studied. As a result, passive (multi -branch single-

tuned) filters were designed for the 5th and 7th harmonic current mitigation and the

distortion levels were reduced from 44.63 % to 0.14 %. This reduction in distortion level

shows how important a filter is to get rid of the ill effects, additional heating, false tripping

and equipment malfunction associated with harmonics.

5.2 Recommendations

The identified power quality problems must be given serious attention and the designed

appropriate solutions should be implemented and installed by the industry to avoid the loss

of money, improve productivity, profitability and early failure of equipment. Based on the

studies and results found, in this thesis, it is strongly recommended that, for the industry to

have the power quality analyzer measuring instrument, Fluke 434/435 three phase.

5.3 Suggestions for Future Work

Power quality assessment should be done regularly, especially on sensitive loads to keep

good performance of the factory and also a complete assessment of power quality problems

should be done. The time allocated for monitoring should be longer, it should be more than

seven days, and this to ensure that, more detailed and complete data could be obtained.

More monitoring points to be allocated in the site, so that more data could be gathered on

the factory.



Appendixes

Appendix A. Loads and sample interruptions

Table A.1 Total electrical load of the factory

Production Line Resistive

Load

ACDL Motor DCL CFPL PSL Idel

Load

UPVC line 1 81 9.9 97.1 110 35.7 37 14

UPVC line 2 45 9.9 92.2 110 24.2 33 13

UPVC line 3 28 6.25 94.1 55 15.9 33 7.2

UPVC line 4 12 46.1 92.1 0 11.1 17 13

HDPE line 5 8.9 35.8 9.23 75 9.65 33 12

HDPE line 6 27 1.1 11.6 160 12.4 33 12

HDPE line 7 27 23.4 11.2 110 19.2 33 12

HDPE line 8 15 60.4 89.3 55.1 15.4 33 12

Geomembrane9 74 70 32.9 352 27.9 33 221

Green sheet10 117 780 41.1 15.4 5.75 0 6

Flat hose 11 4 56.4 5.33 0 0 1 3

Accessories12 16 33.3 639 0 7.5 5.5 326

Total 454 1133 1089 1027 332 286 431



Table A.2 Squeezed Load and transformer data of factory

Load category Power (kw) Transformer category KVA

Load-1 357 T/R-1 1250

Load-2 300

Load-3 225

Load-4 165 T/R-2 709.73

Load-5 160

Load-6 234

Load-7 212 T/R-3 710

Load-8 256 T/R-4 795

Load-9 569

Load-10 954

Load-11 64 T/R-5 789

Load-12 376

Total Load 3872 T/R- (total) 4681.5



Table A.3 Sample recorded data power interruptions in six months

S/N Months Time[minutes] Repetitions External

interruptions

Internal

interruptions

1 July 5580 32 26 6

2 August 1230 35 30 5

3 September 2561 34 30 4

4 October 709 28 25 3

5 November 450 12 10 2

6 December 500 15 14 1

Total 11030 156 151 21



Appendix B. Power quality analyzer and Sample measurement data.

Figure B.1.power quality analyzer and its accessories

Figure B. 2. Power quality analyzer menu display



Figure B.3.Measurement steps on three-phase power

Figure B.4.Sample single and three-phase voltage measured values



Figure B.5. Current harmonic measurement



Appendix C. Electrical Simulink models for simulation

Figure C. 1. Simulink model of voltage unbalance without DVR

Figure C.2. Simulink model of DVR



Figure C.3. Simulink model of voltage unbalance with DVR

Figure 6C. Harmonic Simulink model without filter

Figure 7C. Harmonic Simulink model with filter

Figure C.4. Harmonic Simulink model without filter



Figure C.5. Simulink model of harmonic distortion with filter



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