TRANSFORMER PERFORMANCE MODEL UNDER POWER...

TRANSFORMER PERFORMANCE MODEL UNDER POWER QUALITY

ENVIRONMENT

GARY SOH THIAN LIM

UNIVERSITI TEKNOLOGI MALAYSIA

TRANSFORMER PERFORMANCE MODEL UNDER POWER QUALITY

ENVIRONMENT

GARY SOH THIAN LIM

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2015

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Dedicated to my parents for their endless support and encouragement

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ACKNOWLEDGEMENT

First and foremost, I would like to express my appreciation to my supervisor,

Dr. Dalila Binti Mat Said who has helped me a lot in giving me ideas, opinions and

valuable comment in the making of this thesis. I am deeply grateful to have her as

my supervisor and also my mentor. Her guidance and supervision will help me in the

future life.

In preparing this project report, I was in contact with several people,

researchers, academicians and practitioners. They have contributed towards my

understanding and thoughts. I am also indebted and grateful to my mother whose

love is boundless and my father who constantly encouraged me throughout my

studies. Without their encouragement, enthusiasm and support, this work could not

have been completed.

Last but not least, my sincere appreciation also extends to all my colleagues,

administrative staffs at Faculty of Electrical Engineering, all members of the

Research Management Centre (RMC), UTM and others who have provided

assistance at various occasions. Their views and tips are useful indeed.

Unfortunately, it is not possible to list all of them in this limited space.

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ABSTRACT

The widespread use of static rectification and energy efficient equipment in

end user loads result in a dramatic increase in harmonic content injection towards

transformers connected to upstream power system. Now, due to modern

developments, energy efficient equipment, such as compact fluorescent lamps are

easily available. The use of energy efficient equipment increases rapidly in our

country as saving of electrical energy is the main target of end users and also electric

utility. Meanwhile, these types of equipment contribute to power quality problems

such as harmonic distortion. The harmonic content generated by load causes the

transformer to operate in higher power rating and may cause transformer operating

failure in the long term. This work was initially started with experimentation of

transformer performance analysis in the presence of harmonic events. The objective

of this research is to develop the total harmonic distortion and efficiency model

based on data analysis. Experimental tests are performed to obtain transformer

parameter. Harmonic loads are modelled by utilizing the unique waveform

characteristic of each individual harmonic load type through image processing and

curve fitting methods. Harmonic current injection model has been proposed and

applied using transformer model through the experimental parameter in MATLAB

Simulink. The comparison between harmonic current injection model with the

measured load in terms of true RMS current, apparent power, active power, true

power factor and total harmonic distortion current have been done. An analysis has

also been done on experimental data by comparing the efficiency of transformer with

and without harmonic distortion on identical load type. The developed models for

analysis of transformer efficiency with harmonic distortion indicate goodness of fit

with R-square value close to 1 and Root Mean Square Error of less than 1.

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ABSTRAK

Penggunaan meluas penerusan statik dan peralatan cekap tenaga dalam beban

pengguna akhir menyebabkan peningkatan dramatik dalam suntikan kandungan

harmonik ke arah pengubah yang disambungkan kepada sistem kuasa huluan. Sekarang,

disebabkan oleh perkembangan moden, peralatan cekap tenaga, seperti lampu

pendarfluor padat, mudah didapati. Penggunaan peralatan cekap tenaga meningkat

dengan pantas di negara kita kerana penjimatan tenaga elektrik adalah sasaran utama

pengguna-pengguna akhir dan juga utiliti elektrik. Sementara itu, jenis peralatan

sebegini menyumbang kepada masalah kualiti kuasa seperti herotan harmonik.

Kandungan harmonik yang dihasilkan menyebabkan pengubah beroperasi di peringkat

kuasa yang lebih tinggi dan boleh menyebabkan kegagalan operasi pengubah dalam

jangka masa panjang. Kerja ini bermula dengan eksperimen untuk analisis prestasi

pengubah dalam acara harmonik. Tujuan penyelidikan ini adalah untuk membangunkan

model herotan harmonik seluruh dan kecekapan berdasarkan analisis data. Ujian

eksperimen telah dilaksanakan untuk mendapat parameter pengubah. Beban harmonik

telah dimodel dengan menggunakan keunikan ciri-ciri bentuk gelombang bagi setiap

jenis beban harmonic individu melalui teknik pemprosesan imej dan penyuaian lengkung.

Model suntikan arus harmonik telah dicadangkan dan diaplikasikan dengan model

pengubah melalui parameter eksperimen dalam MATLAB Simulink. Perbandingan

antara model suntikan arus harmonik dengan beban yang diukur dari segi arus RMS

benar, kuasa ketara, kuasa aktif, faktor kuasa benar dan herotan harmonik seluruh arus

telah dilakukan. Analisis juga telah dilakukan ke atas data ujikaji dengan membuat

perbandingan kecekapan pengubah dengan dan tanpa herotan harmonik pada jenis beban

yang sama. Model yang dibangunkan untuk analisis kecekapan transformer dengan

herotan harmonik menunjukkan kebaikan suai dengan nilai R-kuasa dua menghampiri

nilai 1 dan Ralat Punca Min Kuasa Dua kurang daripada 1.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xiii

LIST OF SYMBOLS xviii

LIST OF ABBREVIATIONS xxii

LIST OF APPENDICES xxiv

1 OVERVIEW 1

1.1 Overview 1

1.2 Problem Statement 4

1.3 Objectives of the Study 5

1.4 Scope of Study 5

1.5 Thesis Organization 6

2 LITERATURE REVIEW 8

2.1 Introduction 8

2.2 Advance of Transformer 9

2.2.1 Transformer Faults Report 11

2.3 Power Quality Event 13

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2.3.1 Transformer Research on Power Quality

Issues 15

2.4 Load Variation in Power Quality Environment 18

2.4.1 Electrical Characteristic of Linear Load 19

2.4.2 Electrical Characteristic of Nonlinear Load 20

2.4.3 Comparison of Load Types 23

2.5 Experimental Parameter Transformer 25

2.5.1 Experimental Measurement Model 26

2.5.2 Electromagnetic Fields Analysis Model 27

2.5.3 Estimate and Design Parameter Model 27

2.6 Summary 28

3 RESEARCH METHODOLOGY 30

3.1 Introduction 30

3.2 Research Framework 31

3.3 Experimental Setup 32

3.3.1 Isolation Transformer 33

3.3.2 Variable Transformer 34

3.3.3 Loads 35

3.3.4 Experiment Overall View 39

3.4 Model Development 41

3.4.1 Total Harmonic Distortion Model 42

3.4.2 Efficiency Model 43

3.4.3 Data Fitting Model 44

3.4.4 Transformer Model Parameter 47

3.5 Graph Data Conversion Algorithm 48

3.5.1 Segmentation 50

3.5.2 Pixel Coordinate System 57

3.5.3 Graph Data Scale 57

3.6 Sinusoidal Waveform Model 61

3.6.1 Simplification with Known Frequency 61

3.6.2 Harmonic Waveform Model 63

3.6.3 Simplification with Removal of Bias 63

3.7 Harmonic and Transformer System Model 64

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3.7.1 Harmonic Current Injection Model 65

3.7.2 Transformer Model 65

3.7.3 Overall System Model 66

3.7.4 Analysis Tools 68

3.8 Comparative Study of Load Model 72

3.9 Summary 73

4 SIMULATION RESULTS AND DISCUSSION 75

4.1 Introduction 75

4.1.1 Verification and Comparison of Experiment with

Simulation for Individual Load and Transformer

Component Model 76

4.2 Model of Efficiency Based on Single Load Type 87

4.3 Model of Efficiency Based on Composite Load

with Variation THDI 101

4.4 Comparative Study of Transformer Equivalent

Parameter Separation Based on Weight

Distribution in Simulation Environment 126

4.5 Summary 133

5 CONCLUSION AND FUTURE WORKS 134

5.1 Conclusion 134

5.2 Future Works 137

REFERENCES 139

Appendices A - O 149 - 182

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Reliability of distribution transformers in Europe 12 2.2 Overview of typical load composition 24 2.3 Comparison between linear and non-linear load 25 3.1 Supported File Formats 49

3.2 Windows Bitmap 50

4.1 Description of load types under consideration 75 4.2 Harmonic load parameter result from waveform fitting

model 77

4.3 Comparison of experimental measurement (Exp) and simulation (Sim) results with calculation of error in percentage 81

4.4 Experimental transformer’s open and short circuits measurement results 83

4.5 Transformer’s parameter calculation from measurement results 83

4.6 Simulink transformer model’s open and short circuits simulation results 87

4.7 Comparison experimental and simulation open and short circuits results 87

4.8 Experimental results for measurement with and without

harmonics frequency under same type and unit of loads 89

4.9 Comparison of experimental results between displacement

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power factor and true power factor under same type and unit of loads 93

4.10 Comparison goodness of fitting for different model under consideration 95

4.11 Goodness of fitting for rational model, without harmonic frequency (fund) 98

4.12 Goodness of fitting for rational model, with harmonic frequency (full) 99

4.13 Calculation for transformer’s loss of efficiency with fitted model 100

4.14 Subcase 1 of experimental results with initial 500W linear loads 102




4.18 Total harmonic distortion current (THDI) on secondary side of transformer for each type of load, subcase under consideration 112

4.19 Goodness of fitting for exponential model, of load Type 01 113




4.23 Efficiency of transformer for each type of load, subcase under consideration 119

4.24 Goodness of fitting for power model, of load Type 01 121




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4.28 Transformer parameter weight distribution 127

4.29 Variable parameter with constant load (Type 05=12, Type 03=12, Type 02=12) units 128



4.32 Variable load (Type 05=Num, Type 03=Num, Type 02= Num) with constant parameter (0.8/0.2) 130

4.33 Variable load (Type 05=Num, Type 03=Num, Type 02=

Num) with constant parameter (0.6/0.4) 130

4.34 Variable load (Type 05=Num, Type 03=Num, Type 02= Num) with constant parameter (0.3/0.7) 131

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Failure statistics chart of power transformer by components 3 2.1 Sample load profile 16 2.2 Scheme for inrush current reduction 17 2.3 Interturn nonsinusoidal voltage waveform of VFTO pulse 18 2.4 Sinusoidal waveform of linear load 19 2.5 Maximum True Power Factor Versus THDI 21 2.6 Composition Distortion Waveform 21 2.7 Measured and IEC limits 23 3.1 Research design flow chart 31 3.2 Isolation transformer 34 3.3 Variable transformer (Variac) 35 3.4 Harmonics load bank single line diagram 36 3.5 Harmonics load bank setup: (a) left side view, (b) right side view 37 3.6 Incandescent Light bulbs single line diagram 38 3.7 Incandescent Light bulbs setup 38 3.8 Loads combination block diagram 39 3.9 Circuit diagram of measurement output terminal 40

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3.10 Single line block diagram of experimental setup 41 3.11 Experimental setup 41 3.12 Fluke 435 save screen in BMP format 52 3.13 Graph image file in MATLAB working space (Unit 8) 52 3.14 Pixel intensity of 62 in display range of [0 255] 54 3.15 Pixel intensity of 50 in display range of [0 255] 54 3.16 Pixel intensity of 17 and 26 in display range of [0 255] 54 3.17 Pixel intensity of 14 and 33 in display range of [0 255] 55 3.18 A graph image file waveform (2 cycles) with 240 pixels

heights by 320 pixels wide 56 3.19 Graph image after thresholding (Binary) 56

3.20 Coordinate system 57 3.21 Current waveform data 58 3.22 Block flow diagram 67 3.23 Proposed Simulink system model 67 3.24 Load model verification flow diagram 73 4.1 Measured and simulated waveform comparison of load

Type 01 78 4.2 Measured and simulated waveform comparison of load



Type 05 79

4.5 Measured and simulated waveform comparison of load Type 04 80

4.6 Characteristics of voltage versus current curve of load type under consideration 82

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4.7 Simulation model for open circuit test 84

48 Transformer’s secondary side simulation waveform for 85

both voltage and current of open circuit test

4.9 Simulation model for short circuit test 85 4.10 Transformer’s secondary side simulation waveform for both voltage and current of short circuit test 86

4.11 Comparison of the with (full) and without harmonic

(fund / fundamental) frequency on the efficiency of transformer; Load Type 01=T8(18W); Type 02=T8(36W); Type 03=T5; and Type 05=CFL 90

4.12 Brief comparison of different fitting model for efficiency

versus apparent power under one of the sample data 95

4.13 Model fitted for transformer’s efficiency versus apparent power (VA), without harmonic frequency (fundamental) 96

4.14 Model fitted for transformer’s efficiency versus apparent

power (VA), with harmonic frequency (full) 96

4.15 Model fitted for transformer’s efficiency versus apparent power (VA), both case of with (full) and without (fund) harmonic frequency 97

4.16 Composite of loading condition for each subcase under consideration 101

4.17 Brief comparison of with and without harmonic frequency

on the efficiency of transformer for each subcase under consideration, Load Type 01=T8(18W); Type 02= T8(36W); Type 03=T5; and Type 05=CFL 106

4.18 Brief comparison of with and without harmonic frequency

on the efficiency of transformer: (a) Subcase 1, (b) Subcase 4 107

4.19 Composite of load for nonlinear load Type 05, 5 units in

percentage for; (a) Subcase 1, and (b) Subcase 4 111

4.20 Model fitted for total harmonic distortion current (THDI) on secondary side of transformer for load Type 01, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 113

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4.21 Model fitted for total harmonic distortion current (THDI) on secondary side of transformer for load Type 02, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 114

4.22 Model fitted for total harmonic distortion current (THDI)

on secondary side of transformer for load Type 03, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 115

4.23 Model fitted for total harmonic distortion current (THDI)

on secondary side of transformer for load Type 05, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 116

4.24 Model fitted for total harmonic distortion current (THDI) on secondary side of transformer for all load Type, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 118

4.25 Model fitted for efficiency of transformer for load Type 01, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 120

4.26 Model fitted for efficiency of transformer for load Type 02,

subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 121

4.27 Model fitted for efficiency of transformer for load Type 03,

subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 122

4.28 Model fitted for efficiency of transformer for load Type 05, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base consumption of linear load) 123

4.29 Model fitted for efficiency of transformer for all load Type, subcase under consideration (Subcase 1= 500W, Subcase 2=1000W, Subcase 3=1500W, Subcase 4=2000W; base

xvii

consumption of linear load) 126

4.30 Efficiency versus variable K1/K2 curves for constant units of loads in three cases; (i)Num=12 Units, (ii) Num= 20 Units, and (iii) Num=27 Units 129

4.31 Efficiency versus Number of Loads for constant of K1/

K2 in three cases; (i) K1/K2=0.8/0.2, (ii) K1/K2=0.6/0.4, and (iii) K1/K2=0.3/0.7 131

4.32 Efficiency versus Number of Loads for constant of K1/K2 in selected cases: (iii) K1/K2=0.3/0.7 nonlinear load (THDI

approximate 42%) compared with an additional linear load (THDI <.1.6%) 132

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LIST OF SYMBOLS

imgA Magnitude of M number of data with N unit substrate the

minimum magnitude value of N

rmsA Root mean square current

peakA Peak current

, ,A B C Coefficient or constant value

( )B Flux density column matrix

imgB Median value of Aimg

imgC Bias value of Aimg toward the horizontal origin axis

imgD Inverse value of Cimg

img peakD Peak value of current waveform

,rmsimgD True Root mean Square value of current waveform from

Measurement

sF Sampling rate of the data saved in the image

WF Frequency of the waveform

HLF Harmonic loss factor

H Magnetic field strength

h Harmonic order

DI Actual magnitude value of current waveform

, thH i deviceI Harmonic waveform function of ith equipment

,TotalHI The individual modelled device controlled with Ni units add

together

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hI , hi , Hi RMS current at harmonic order of h

LI Load current

ABCI Three phase current

ocI Input current during open circuit test

scI Rated current

1i , 1I Current, fundamental frequency component

oi Direct current

pi In-phase line current

qi Reactive current

( )M Equivalent magnetization column matrix

{ }max imgA Maximum value of Aimg

{ }min imgA Minimum value of Aimg

{ }max imgD Maximum value of Dimg

{ }min N Minimum value of N

sn Total number of sample

Wn Number of cycle of the waveform

HP Active power, harmonic frequency components

ECP Total eddy-current losses

EC OP − Windings eddy-current losses

ocP Input power during open circuit test

scP Input power during short circuit test

1P Active power, fundamental frequency component

distortionPf Distortion power factor

cR Core loss resistance

eqR Equivalent winding resistance

1 1,R X Primary winding parameter

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2 2,R X Secondary winding parameter

,t wr Winding turn ratio

residualSS Sum of square of residuals

totalSS Sum of square of ( iY -_Y )

( )T Coefficient matrix

sT Interval period between two of the sample

WT Period of the waveform within nW cycle

t Time frame of each sampled data in second

su Voltage measured in secondary winding

ABCV Three phase voltage

fundV Voltage with fundamental frequency

ocV Rated voltage

scV Input voltage during short circuit test

peakV Peak voltage

rmsV Root mean square voltage

hv Voltage, harmonic frequency components

1v Voltage, fundamental frequency component

fullVA Apparent power which consider harmonic frequency

fundVA Apparent power which consider fundamental frequency only

fullW Power which consider harmonic frequency

fundW Power which consider fundamental frequency only

iX Independent variable vector

mX Magnetizing reactance

eqX Equivalent leakage reactance

iY Response variable with ith response

,residual iY Residual values

_Y Mean value of observation data

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,n harmonicy Harmonic waveform function

SHZ Short circuit impedances

% f , THD THD relative to the fundamental

%r , THDR THD relative to the root mean square

β , α Regression coefficient vector

0pλ Residual flux

iε ith noise term

%ε Percentage of error

φ Phase angle

nφ Phase angle of n harmonic order

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LIST OF ABBREVIATIONS

AC, ac Alternating current

ASDs Adjustable-speed drives

BNC Bayonet Neill–Concelman or Baby N Connector

CF Crest factor

CFL Compact fluorescent lamp

DC, dc Direct current

DFT Discrete Fourier Transform

DPF Displacement power factor

FE Finite Element

FFT Fast Fourier Transform

FULL Measurement included harmonic frequency

Fund Measurement with fundamental frequency

GA Genetic Algorithm

GUI Graphical user interface

HV High voltage

IEC International Electrotechnical Commission

LV Low voltage

MCB Miniature circuit breaker

PF, tpf True power factor

PLT Long term flicker

RCCB Residual current circuit breaker

RLE Run-Length encoding Compression

RMS Root mean square

RMSE Root mean square error

SSE Sum of square error

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THD Total harmonic distortion

T5 Fluorescent T5 lamp

T8 Fluorescent T8 lamp

Variac Variable transformer

VFTO Very Fast Transient Overvoltages

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A MATLAB coding- loss of efficiency 149 B MATLAB coding waveform image extraction data 150 C MATLAB coding waveform image data scale 152 D MATLAB coding waveform data fitting 153 E MATLAB Simulink harmonic injection model 155 F MATLAB Simulink load waveform generation and coding waveform for comparison 156 G MATLAB Simulink load characteristic with voltage

versus current and coding for graph plot 157 H MATLAB Simulink model assessment of load 158 I MATLAB coding to run Simulink model 159 J Electromagnetic phenomena categories 171 K Review of equations 173 L Photo of experiment 174 M Fluke analyser 176 N Laboratory scale test 180 O Publications 182

1

CHAPTER 1

OVERVIEW

1.1 Overview

Nowadays, the widespread application of static rectification and energy-

efficient equipment in end user loads with transformers having small (5M to 40MVA)

and medium (40M to 250MVA) power range has resulted in a dramatic increase in

the harmonic components of the load current for this equipment. The use of energy-

efficient equipment in our country is increasing rapidly as end users and electric

utility companies are looking forward to saving electrical energy. Due to modern

developments, energy efficiency equipment such as compact fluorescent lamp is

easily available. These types of equipment give rise to the power quality problem

such as harmonic distortion. Consequently, increased usage of these types of

equipment gives rise to the harmonics on the transformer. It is also well known that

higher harmonic content in the current can cause higher current loss in winding

conductors and structural parts linked by the transformer leakage flux field, and

consequently, these losses are dissipated as heat and gives rise to higher operating

temperature than normal.

Transformers are one of the most important components from the generating

station to end-user equipment; which play an important role in minimizing the losses

throughout the stage by stepping up or stepping down the voltage. In end-user

2

equipment, transformer is used to regulate the voltage from single phase 240V ac to

the required output voltage.

Common sources of harmonics in the industrial sector are electrical ballast,

dc motor drives and rectifiers. In this modern era, direct current power supply to the

load of end-user equipment involves the use of rectifiers, since loads connected to

the power supply in the end-user equipment will result in current distortion [1].

Voltage distortion and current distortion drawn by these loads are one of the power

quality issues on the transformer. Losses in transformer can be categorized into no-

load and load losses. The no-load loss arises from the voltage excitation of the core

and eddy currents and magnetic hysteresis. Load loss occurs mainly from the

resistive losses in the conducting material of the windings [2]. There are three

factors resulted by the increased transformer heating when the load current includes

harmonic components.

(a) RMS current: Harmonic currents may cause the transformer RMS

current being higher than its capacity, if the transformer is sized only

for the kVA requirements of the load;

(b) Eddy-current losses: These are due to the magnetic fluxes which

caused induced currents in a transformer;

(c) Core losses: In the presence of harmonics, nonlinear core losses may

increase depends on the effect of the harmonics on the design of the

transformer core and applied voltage.

There are reports regarding failures in transformers under normal operating

condition with high levels of harmonic currents [3], such as nonsinusoidal currents

drawn by nonlinear load causing excessive loss and heating [4] in transformer.

Transformers are commonly constructed to utilize at rated frequency and apparent

power. Nowadays, with the presence of nonlinear loads, harmonic distortion often

3

result in higher losses on transformer, which can cause abnormal temperature rise

and excessive winding losses [5].

Figure 1.1 shows the well organised document and studied scattering failure

data to identify the critical component of transformer. These figures are not

appropriate to simply reach conclusions on the causes of transformer fault. This is

because the degradation of transformer data was taken under its normal and

abnormal operating conditions. Maintenance works are vital to restore the condition,

but costly in terms of outage duration, disruption of production line, restore and

necessary replacement. With statistical analysis, it is possible to describe the ageing

processes of power transformer components statistically. In year 2012, Voros et al.

reviewed an expert system which evaluates condition of transformer with the status

diagram, technical and statistic support to manage transformer lifecycle [6]. Now,

the preventive maintenance costs have become more of primary concern. In year

2014, Suwanasri proposed asset management of transformer with failure statistical

analysis to diminish operating and maintenance costs [7].

Core

Tap-changer

Leakage

Bushing

Windings

Others

12%

41%

3%

19%

12%

13%

Figure 1.1 Failure statistics chart of power transformer by components as in [8].

4

1.2 Problem Statement

Harmonic distortion is one of the major power quality concerns for electric

utility companies. The non-linearity of end user loads which produces harmonic

distortion will affect transformer performance. The increasing use of non-linear

loads being connected to the transformer also magnifies the power quality problems.

Distortion of sinusoidal current waveforms due to harmonics causes increases in

transformer winding losses and possible loss of equipment lifespan.

Previously, other researchers took measurement at the power substation

which did not provide details of type of loads operating at that time frame for the

data taken. The main focus is on the calculations which relate the losses with and

without harmonic to a harmonic distortion factor. This formulation does give an idea

of the losses increment between fundamental frequency and harmonic frequencies,

but does not model the performance of the transformer under condition of loads

quantity and composition in relation with efficiency and harmonic distortion level.

This study attempts to fill in this research gap. Therefore, it is necessary to develop

model which able to provide and compare detail of the performance of a transformer

under the harmonic event. The parameters involved in developing the model and

method to relate the variables with a suitable regression model should be investigated.

The model which can provide detailed comparison with different input parameter

more precise. This developed model is hoped able to be a helping hand in analyzing

transformers with harmonic issues. This research involved to setup a laboratory

scale experiment initially to collect data which is costly and time consuming.

Correspondingly, the cost and expenses can be reduced by avoiding the need of

setting up similar experimental work in the future.

5

1.3 Objectives of the Study

This study embarks on the following objectives:

(a) to develop model of efficiency with variation of load,

(b) to model the trend of total harmonic distortion under variation of load

composition,

(c) to analyze the model in term of harmonic distortion and transformer

efficiency, and

(d) to compare the variation in stage of separation based on weight

distribution for transformer equivalent parameter in simulation

environment.

1.4 Scope of Study

This research develops a performance model of transformer with start-up

with an experiment setup. The data collection and analysis plan provide sufficient

amount of information that are relevant to problem of study by using the available

resources more efficiently. The factors include transformer efficiency, loads

composition, harmonic distortion level, apparent power, fundamental frequency, and

harmonic frequency. The overall data collection and analysis plan were utilized to

consider how the experimental factors fit together into a model that would fulfil the

specific objectives of the experiment and satisfy the practical constraints of time and

money. Understanding how the relevant variables fit into the design structure would

indicate whether appropriate data could be collected in a way that permits an

objective analysis that leads to valid inferences with respect to the stated problem.

The transformer and loads components from the experimental work were

digitized into the simulation environment model by analyzing the measurement data.

6

Each model of the components was compared individually before being combined to

build the complete system model. One of the main motivations for developing a

simulation model or using any other modelling method is that it will be an

inexpensive approach to gain important insights on when the costs, risks or logistics

of manipulating the real system of interest are limited or prohibitive.

In this study, all apparatus needed for measurement and test equipment were

identified to ensure the measurement units or test equipment were set up according to

the user manual provided, if any. This was to minimise risk of making error of

results with wrong setting, which would waste time in starting over again in the

measurement process. Another reason was to avoid damage to the equipment and

also as a cautious step for personal safety. Even though the end user equipment

considered as loads were normal household’s lighting load, caution and awareness

step should be taken from time to time when experimental work is being conducted.

1.5 Thesis Organization

This thesis composes of six chapters, which are arranged as follows:

Chapter 1 describes the overview of the study, which includes the objectives,

scope of study, problem statement and methodology throughout the study. Chapter 2

reviews the past research work, and related on-going transformer research on power

quality issue. Transformer component model with its measured parameters are also

described in this chapter.

Chapter 3 presents in depth explanation of each part of the components

involved in the experimental work. Power quality analyser applied for measurement

and its merit for quantifying the harmonic level are discussed in detail. This chapter

7

also discusses the application of regression model on experimental data formulation

and goodness indication of the fitting.

The overall system model with harmonic current injection model and

transformer model in simulation environment are also presented in Chapter 3. The

programming of the image processing data requiring mathematical algorithm on load

waveform is also discussed. The mathematical theory involved in analysis tool

applied in the simulation is presented as well.

Chapter 4 presents explanation on the data analysis with the aim of

developing mathematical models using the regression method to describe the studied

relationship between the variability of the measurement results. Discussion of the

simulation results is also included. Aspects such as transformer’s efficiency, total

harmonic distortion level and apparent power consumption are discussed as well.

Finally, Chapter 5 concludes the study and suggests several potential future works

for improving the current work.

139

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