Faculty of Electrical Engineering

INSULATOR SURFACE CONDITION MONITORING SYSTEM FOR

LEAKAGE CURRENT ANALYSIS

Nur Qamarina Binti Zainal Abidin

Master of Science In Electrical Engineering

2015

INSULATOR SURFACE CONDITION MONITORING SYSTEM FOR LEAKAGE

CURRENT ANALYSIS

NUR QAMARINA BINTI ZAINAL ABIDIN

A thesis submitted in fulfilment of the requirements for the degree of Master of Science in Electrical

Engineering

Faculty of Electrical Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2015

DECLARATION

I declare that this thesis entitle “Insulator Surface Condition Monitoring System For

Leakage Current Analysis” is the result of my own research except as cited in the

references. The thesis has not been accepted for any degree and is not concurrently

submitted in candidature of any other degree.

Signature : ......................................................

Name : Nur Qamarina binti Zainal Abidin

Date : ......................................................

APPROVAL

I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in

terms of scope and quality for award of Master of Science in Electrical Engineering.

Signature : ......................................................

Supervisor Name : Dr. Abdul Rahim Bin Abdullah

Date : ......................................................

DEDICATION

To my beloved mother and family

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ABSTRACT

There are several ageing factors that affect the long term performance of insulating material such as electrical stress, biological attack, and outdoor weathering contamination. Leakage Current (LC) is one of the key methods of measuring the insulator surface conditions which can cause tracking, erosion and flashover. Hence, an automated monitoring system is needed to reduce diagnostic time, rectify severity and ensure quality of insulator performance. This research presents the development of leakage current monitoring system to analyse insulator surface condition using Time-Frequency Distribution (TFD). To develop the system, a pre-information of the leakage current signal analysis is needed. Many previous researchers used Fast Fourier Transform (FFT) method for the analysis which gives spectral information; but it has some limitations in non-stationary signal, for example it does not provide temporal information. In this research, spectrogram is used to analyse the leakage current signals that consist of multi-frequency components and magnitude variations. From the Time-frequency representation (TFR) obtained using the time-frequency distribution, parameters of leakage current signal are calculated such as instantaneous of root mean square (RMS) current, fundamental RMS current, total harmonic distortion, total non-harmonic distortion, and total waveform distortion. The leakage current signals have different states such as capacitive, resistive, symmetrical and unsymmetrical waveforms that classifies the surface condition of the polymeric insulation. Tracking and erosion tests based on BS EN 60587-2007 standard are developed and constructed to capture the set of those leakage current states. Then, the leakage current signals are captured and transfer to personal computer using data acquisition system (DAQ) for monitoring and storing purpose. Graphical User Interface (GUI) is developed using Visual Basic (VB) for the real time analysis of the leakage current for insulator surface condition monitoring system. At the end of this research, the developed system shows that it is appropriate and reliable to implement the leakage current monitoring system for determining the leakage current characteristic of insulating surface condition.

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ABSTRAK

Terdapat beberapa faktor yang memberi kesan penuaan prestasi jangka panjang dari bahan penebat seperti tekanan elektrik, serangan biologi, dan pencemaran luluhawa luar. Kebocoran Arus adalah salah satu daripada kaedah utama mengukur keadaan permukaan penebat yang boleh menyebabkan pengesanan, hakisan dan jambatan kilat. Oleh itu, satu sistem pemantauan automatik diperlukan untuk mengurangkan masa diagnostik, memperbaiki tahap penebat dan memastikan kualiti prestasi penebat. Kajian ini membentangkan pembangunan sistem pemantauan kebocoran arus untuk menganalisis keadaan permukaan penebat menggunakan Taburan Masa Frekuensi (TFD). Untuk membangunkan sistem ini, pra-maklumat analisis isyarat arus kebocoran diperlukan. Ramai penyelidik sebelumnya telah menggunakan Fourier cepat ubah (FFT) iaitu kaedah yang memberikan maklumat spektrum kepada analisis kebocoran arus, tetapi ia mempunyai beberapa batasan dalam isyarat tidak seimbang, misalnya ia tidak dapat memberi maklumat yang sementara. Dalam kajian ini, spectrogram digunakan untuk menganalisis isyarat arus kebocoran yang terdiri daripada komponen multi-frekuensi dan variasi magnitud. Dari Perwakilan Frekuensi Masa (TFR) yang diperoleh dengan menggunakan taburan masa-frekuensi, parameter isyarat arus bocor dikira, seperti arus bocor punca min kuasa dua (RMS), arus bocor RMS, jumlah herotan harmonik, jumlah herotan bukan harmonik, dan jumlah herotan bentuk gelombang. Isyarat arus bocor memiliki corak yang berbeza seperti kapasitif, rintangan, simetri dan bentuk gelombang simetri yang mengklasifikasikan keadaan permukaan penebat polimer. Penjejakan dan hakisan ujian yang mengikut konsep BS EN 60587-2007 dibina bagi menangkap set corak kebocoran arus. Kemudian, isyarat kebocoran arus ditangkap dan dipindahkan ke komputer peribadi yang menggunakan sistem perolehan data (DAQ) untuk memantau dan menyimpan. Pengguna grafik muka (GUI) dibangunkan dengan menggunakan Visual Basic (VB) untuk analisis masa sebenar arus bocor untuk sistem pemantauan keadaan permukaan penebat. Pada akhir kajian ini, sistem tersebut menunjukkan ianya sesuai dan boleh dipercayai untuk melaksanakan sistem pemantauan kebocoran arus untuk menentukan ciri-ciri kebocoran arus keadaan permukaan penebat.

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ACKNOWLEDGEMENT

All praise to the almighty Allah s.w.t. I would like to express my deepest gratitude to my

supervisor, Dr. Abdul Rahim bin Abdullah for introducing me to the topic as well for the

support on the way, useful comments and ideas, excellent guidance, remarks, engagement,

caring, and patience through the learning process of this master thesis. Same also as Dr.

Aminudin bin Aman for providing me an excellent atmosphere for doing research. I feel

motivated and encouraged and without these two people, this project would not have been

materialized. I am also would like to thank my co-supervisor En. Khairul Anwar bin

Ibrahim, Universiti Teknikal Malaysia Melaka Zamalah Scheme’s committee, and project

grant of RACE/F1/TK3/UTEM/10 that has given me an opportunity that financially

supported my research.

Apart from the efforts of me, the success of any project depends largely on the

encouragement and guidelines of many others. I would also like to thank my laboratory

mate, Nurbahirah binti Norddin and Azhar bin Sulaiman for the meaningful collaboration

and discussion which also contributed in this project. My other fellow postgraduate

students of ADSP (Advance Digital Signal Processing) lab members should also be

recognised for their support.

Also not to forget my family that has always been there to support me all the way, and my

loved ones, who have supported me throughout entire process, both by keeping me

harmonious and helping me putting pieces together, my greatest husband.

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TABLE OF CONTENT

PAGE

DECLARATION i APPROVAL ii DEDICATION iii ABSTRACT i ABSTRAK ii ACKNOWLEDGEMENTS iii TABLE OF CONTENTS iv LIST OF FIGURES vii LIST OF TABLES x LIST OF ABBREVIATIONS xi LIST OF SYMBOLS xiii LIST OF PUBLICATIONS xiv LIST OF APPENDICES xvi CHAPTER 1. INTRODUCTION 1

1.1 Overview of Research Background 1 1.2 Motivation of Research 3 1.3 Problem Statement 4 1.4 Objectives of Research 5 1.5 Scopes of Work 6 1.6 Contributions of Research 8 1.7 Thesis Organization 8

2. LITERATURE REVIEW AND THEORETICAL ANALYSIS 10

2.1 Introduction 10 2.2 Insulating Materials 11

2.2.1 Polymeric Insulation (Polypropylene) 11 2.2.2 Accelerated Ageing Test 15

2.3 Leakage Current of High Voltage Insulators 17 2.3.1 Leakage Current Characteristics 18 2.3.2 Leakage Current Analysis Techniques 23

2.4 Signal Processing Techniques 26 2.4.1 Fast Fourier Transform (FFT) 27 2.4.2 Short Time Fourier Transform (STFT) 28 2.4.3 Spectrogram 29 2.4.4 Wavelet Transform 29 2.4.5 S-Transform 30

2.5 Surface Condition Monitoring System 31 2.6 Summary 31

3. RESEARCH METHODOLOGY 33

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3.1 Introduction 33 3.2 Research Framework 34 3.3 Hardware Development 36

3.3.1 Incline Plane Tracking Test Setup 37 3.3.2 Measuring and Protection Circuit 42 3.3.3 Material Preparation 43 3.3.4 Non-standard Test Procedure for Incline Plane Tracking Test 45 3.3.5 State of Leakage Current Signal Condition 46

3.4 Simulation of Leakage Current Analysis 50 3.4.1 Fourier Transform 51 3.4.2 Spectrogram 52 3.4.3 Leakage Current Signal Parameters 54 3.4.3.1 Instantaneous RMS Current 55 3.4.3.2 Instantaneous RMS Fundamental Current 55 3.4.3.3 Instantaneous Total Harmonic Distortion 55 3.4.3.4 Instantaneous Total Inter-Harmonic Distortion 56 3.4.3.5 Instantaneous Total Waveform Distortion 56

3.5 Leakage Current Monitoring System 57 3.5.1 Data Acquisition (DAQ) System 58 3.5.2 Software for Leakage Current Monitoring System 61 3.5.3 Surface Condition Classification of Polymeric Insulation 64

3.6 Summary 66 4. RESULTS AND DISCUSSION 67

4.1 Introduction 67 4.2 Inclined Plane Tracking (IPT) Test 67

4.2.1 Hardware of Incline Plane Tracking Test 68 4.2.2 Polypropylene Material 71

4.3 Leakage Current Analysis Results 72 4.3.1 Leakage Current Patterns for Polypropylene 72 4.3.2 Leakage Current Signal Analysis using Fast Fourier Transform 74 4.3.3 Leakage Current Signal Analysis using Spectrogram 76 4.3.4 Classification of Leakage Current Signal for Polypropylene 80

4.4 Surface Condition Monitoring System 83 4.4.1 Timing Parameters 85 4.4.2 Time Frequency Representation 86 4.4.3 Leakage Current Parameters 87 4.4.4 Data Logger 89 4.4.5 Signal Classifier 90

4.5 System Performance Verification 91 4.5.1 Performance Comparison between System and Simulation 91 4.5.2 Surface Condition Classification 97

4.6 Summary 98

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5. CONCLUSION 99 5.1 Summary of Research 99 5.2 Attainment of Research Objectives 101 5.3 Significance of Research Objectives 102 5.4 Suggestion for Future Work 102

REFERENCES 104 APPENDICES 110

vii

LIST OF FIGURES

FIGURE TITLE PAGE

1.1 General illustration of insulator 1

2.1 A criterion separating leakage current into components 19

2.2 Leakage current for silicon rubber (a) dry surface (b) dry band (c) surface discharge (d) partial arch (e) fully arch 21

2.3 Stationary Signals 23

2.4 Non-stationary signal 23

3.1 Research Framework 34

3.2 Experiment setup for incline plane tracking test a) IPT setup b) DAQ card c) Monitoring devices 37

3.3 Installation of test specimen for incline plane tracking test 39

3.4 Non-ionic wetting agents Triton X100 39

3.5 Conductivity Testing Meter 40

3.6 Peristaltic pump 40

3.7 Measuring and Protection Circuit 42

3.8 Sample material dimension 44

3.9 Hot-press machine (Gotech) 44

3.10 Pellet filled into mould plate 45

3.11 Finished material 45

3.12 Typical variation of leakage current waveform 47

3.13 Capacitive leakage current signal 48

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3.14 Resistive leakage current signal 49

3.15 Symmetrical leakage current signal 49

3.16 Unsymmetrical leakage current signal 49

3.17 Time-frequency representation 53

3.18 Process flow of analysing leakage current parameters 54

3.19 Test setup to measure the leakage current of the insulator 58

3.20 NI DAQ 6009 USB b) Device block diagram 59

3.21 Block diagram for leakage current measurement using LabVIEW 60

3.22 Configuration of leakage current signal analysis 63

3.23 Hardware design for software system 63

4.1 a) Block diagram of incline plane tracking test b) Developed hardware of the incline plane tracking test 68

4.2 Voltage Divider Probe and Power Resistor 69

4.3 Electrical circuit for start, stop button and indicator lamp 70

4.4 Sparking occurred during incline plane tracking test 71

4.5 Polypropylene material condition shows erosion 72

4.6 Leakage current signal for polypropylene material 73

4.7 Leakage current patterns for polypropylene material (a) capacitive (b) resistive (c) symmetrical discharge (d) unsymmetrical discharge 75

4.8 Capacitive type for polypropylene material 76

4.9 Capacitive type for polypropylene material: 77

4.10 Leakage current of polypropylene material 78

4.11 Discharge activities on polypropylene material: a)frequency spectrum b) Time-frequency representation c)Total harmonic distortion d)Total non-harmonic distortion e)Total waveform distortion 79

4.12 Capacitive type for polypropylene material; a)capacitive signal b)spectrogram c)Total waveform distortion 80

4.13 Resistive type for polypropylene material; a)resistive signal b)spectrogram c)Total waveform distortion 81

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4.14 Symmetrical type for polypropylene material; a)symmetrical signal b)spectrogram c)Total waveform distortion 82

4.15 Unsymmetrical type for polypropylene material; a)unsymmetrical signal b)spectrogram c)Total waveform distortion 83

4.16 Completed surface condition monitoring system 84

4.17 Time frequency representation 86

4.18 Unsymmetrical leakage current parameters 88

4.19 Recorded analysed leakage current signal data 89

4.20 Data of input leakage current signal 90

4.21 Recorder and input data loader 90

4.22 Comparison of analysis results between visual basic and MatLab for leakage current symmetrical pattern 96

B.0.1 Incline plane tracking schematic diagram 114

B.0.2 Incline plane tracking test setup 114

B.0.3 Incline plane tracking final test development 115

B.0.4 Step for material preparation 115

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LIST OF TABLES

TABLE TITLE PAGE

1.1 Proposed system’s interests 7

2.1 Comparison between non polymeric and polymeric 12

2.2 Strengths and limitations of homo polypropylene 14

2.3 Comparison accelerating ageing test method 15

3.1 Components in the online monitoring system 62

4.1 Range value for power resistor 69

4.2 Comparison of analysis results between visual basic and MatLab for leakage current capacitive pattern 93

4.3 Comparison of analysis results between visual basic and MatLab for leakage current resistive pattern 95

4.4 Rules Base Leakage Current Surface Condition Classification 97

C.1 Polypropylene Performances 116

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LIST OF ABBREVIATIONS

HV - High Voltage

PVC - Polyvinylchloride

LC - Leakage Current

FFT - Fast Fourier Transform

TFD - Time Frequency Distribution

IPT - Inclined Plane Tracking

RMS - Root Mean Square

THD - Total Harmonic Distortion

TnHD - Total non-Harmonic Distortion

TWD - Total Waveform Distortion

TFR - Time Frequency Representation

VB - Visual Basic

GUI - Graphic User Interface

TNB - Tenaga Nasional Berhad

DC - Direct Current

HVDC - High Voltage Direct Current

EAP - Early Aging Period

TP - Transition Period

LAP - Late Aging Period

FT - Fourier Transform

DFT - Discrete Fourier Transform

STFT - Short Time Fourier Transform

Hz - Frequency unit, Hertz

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ADC - Analogue to Digital Converter

NI-DAQ - National Instrument Data acquisition

USB - Universal Serial Bus

V - Volts

PP - Polypropylene

UTeM - Universiti Teknikal Malaysia Melaka

DAQ - Data Acquisition

P.U - Per-unit System

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LIST OF SYMBOLS

w(t) - Observation window

fs - Sampling frequency

f0 - Fundamental frequency

h - Harmonic

ts - Sampling period

n - Integer

IRMS (t) - Instantaneous Root Mean Square Current

I1RMS (t) - Instantaneous Root Mean Square Fundamental Current

ITHD(t) - Instantaneous Total Harmonic Distortion

ITnHD(t) - Instantaneous Total non-Harmonic Distortion

ITWD(t) - Instantaneous Total Waveform Distortion

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LIST OF PUBLICATIONS

1. Publications

N. Q. Zainal Abidin, A. R. Abdullah, N. Norddin, A. Aman (2013). “Online Surface Condition Monitoring System using Time Frequency Distribution on High Voltage Insulator." Australian Journal of Basic and Applied Sciences.

Norddin, N., A. R. Abdullah, N. Q. Zainal Abidin, A. Aman (2013). "High Voltage Insulation Surface Condition Analysis using Time Frequency Distribution." Australian Journal of Basic and Applied Sciences.

N. Norddin, A. R. Abdullah, N. Q. Z. Abidin, and A. Aman, “Automated Classification System for Polymeric Insulation Surface Conditions” Engineering Letters. (Accepted for IAENG Journal).

2. Proceeding International Conferences / Seminar

Zainal Abidin, N. Q., A. R. Abdullah, et al. (2013). Online surface condition monitoring system using time-frequency analysis technique on high voltage insulators. Power Engineering and Optimization Conference (PEOCO), 2013 IEEE 7th International.

Abidin, N. Q. Z., A. R. Abdullah, et al. (2012). Leakage current analysis on polymeric surface condition using time-frequency distribution. Power Engineering and Optimization Conference (PEOCO) Melaka, Malaysia, 2012 Ieee International.

Abidin, N. Q. Z., A. R. Abdullah, et al. (2012). Online Leakage Current Monitoring System using Time-Frequency Distribution on High Voltage Insulator. Power and Energy Conversion Symposium (PECS 2012). Melaka, Malaysia. Norddin, N., A. R. Abdullah, et al. (2013). Polymeric insulation surface condition analysis using linear time frequency distributions. Power Engineering and Optimization Conference (PEOCO), 2013 IEEE 7th International.

Sulaiman, A., A. R. Abdullah, et al. (2013). Performance analysis of high voltage insulators surface condition using Time-Frequency Distribution. Power Engineering and Optimization Conference (PEOCO), 2013 IEEE 7th International.

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Abdullah, A. R., N. Norddin, et al. (2012). Leakage current analysis on polymeric and non-polymeric insulating materials using time-frequency distribution. Power and Energy (PECon), 2012 IEEE International Conference.

Norddin, N., A. R. Abdullah, et al. (2012). Leakage Current Analysis of Polymeric Insulation using Linear Time Frequency Distribution. Power and Energy Conversion Symposium (PECS 2012). Melaka, Malaysia.

3. Exhibition

PECIPTA Silver Medal for the the invention Online High Voltage Insulator Surface Condition Monitoring System at the International Conference and Exposition on Invention of Institutions of Higher Learning PECIPTA 2013 in 7-9 Nov, Kuala Lumpur, Malaysia.

Awarded ITEX bronze medal for the invention “Online High Voltage Insulator Surface Condition Monitoring System” at the 24th International Invention, Innovation & Technology Exhibition ITEX 2013 Kuala Lumpur, Malaysia from 9th-11th May 2013.

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A MatLab Simulation 111

B Inclined Plane Tracking (IPT) development 114

C Polypropylene Performances 116

CHAPTER 1

1. INTRODUCTION

1.1 Overview of Research Background

Two of the most important components in high voltage (HV) engineering or its

applications, are conductors and insulator. Conductors are used to carry current to the

desired paths while insulators prevent the flow of currents in undesired paths, as shown in

Figure 1.1 (Ronald and Duccan, 2004). The principal media of insulation used for

insulators are gases, vacuum, liquid, solid, or a composite (combination). Among them,

solid dielectric materials are used in all kinds of electrical apparatus and devices to insulate

the current carrying part from one another when they operate at different voltages.

Leakage current will flow through the protective ground conductor to ground. One

of the main contributors that leads to the occurrance of leakage current is the

contamination on the surface of the insulators. Measurement of leakage current is one of

most critical steps to find information on how to minimize the flashover caused by

Figure 1.1 General illustration of insulator

2

pollution insulators, and better if it requires additional information from measurements and

analysis of the pollution (Ramirez et al., 2012). For leakage current performance, one

factor that should be controlled is the flashover mechanism due to dry band formation on

the surface. Basically, leakage current signal that leads to surface flashover consists of

capacitive current, resistive current, non-linear current and non-linear with discharge

current (Bollen and Gu, 2006). Measurement of the leakage current such as amplitude,

pulse, accumulated charge and discharge duration has been used to provide information on

degradation (Fernando and Gubanski, 1999c). For this reason, measurements of leakage

current are often performed in order to evaluate the performance of the material surface

condition.

Incline Plane Tracking (IPT) test that complies to the BS EN 60587-2007 standard

is conducted on polypropylene polymeric to simulate a set of different leakage current

patterns; from capacitive state, resistive state, symmetrical and unsymmetrical state.

Leakage current is normally analysed in frequency domains, and the fast Fourier transform

(FFT) is commonly used for transformation technique. However, leakage current signals

are usually in non-stationary pattern especially during dry-band condition and surface

discharge. Therefore, to overcome these limitations, time frequency distribution (TFD) is

used.

Time frequency distributions (TFDs) are developed to represent time-varying signal

jointly in time and frequency representation (TFR) (Radil et al., 2007). Non-stationary

signals in electrical engineering brings a challenges for signal processing which serves the

idea for applying joint time frequency representations. Conventional techniques that are

currently used for signal monitoring are based on visual inspection of voltage and current

waveforms. In this research, an automated signal classification system using spectrogram

analysis is developed to identify, classify as well as provide the information of the signal.

3

1.2 Motivation of Research

High voltage insulators form an essential part of the high voltage electric power

transmission systems. Any failure in the performance of high voltage insulators will result

in considerable loss of capital, as there are numerous industries that depend upon the

availability of an uninterrupted power supply. The importance of the research on insulator

pollution has been increased considerably with the rise of the voltage of transmission lines

since outdoor insulators are being subjected to various operating conditions and

environments.

Surface discharge is a common electrical discharge that normally occurs on outdoor

insulators under wet and contaminated conditions. The surface of the insulators is covered

by airborne pollutants due to either natural or industrial pollutants, or mixed between the

two. Contamination on the surface of the insulators enhances the chances of flashover.

Under dry conditions the contaminated surfaces do not conduct any leakage current, and

thus contamination is of little importance in dry periods (Gorur and Olsen, 2006). As the

surface become moist due to rain, fog or dew, the pollution layer becomes conductive

because of the presence of ionic solids. Pollution flashover, ageing, tracking and erosion

that observed on insulators used in high voltage transmission, is one of the most important

problems for power transmission. These kind of pollutions are very complex problem due

to several reasons such as modelling difficulties of the insulator complex shape, different

pollution density at different regions, non-homogenous pollution distribution on the

surface of insulator and unknown effect of humidity on the pollution (Dhahbi-Megriche

and Beroual, 2000).

The performance of insulators under polluted environment is one of the guiding

factors in the insulation coordination of high voltage transmission lines. On the other hand,