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PERPUSTAKAAN UTHM

*30000002103464*

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

PENGESAHAN STATUS LAPORAN PROJEK SARJANA

PARTIAL DISCHARGE DETECTION FOR CONDITION MONITORING OF AN 11-KVXLPE CABLE

Saya NOR AKMAL BT MOHD JAMAIL mengaku membenarkan laporan projek sarjana ini disimpan di Pefpustakaail dengaa syafat-syafat kegunaan sepeiti befikut:

1. Tesis adalah hakmilik Universiti Tun Hussein Onn Malaysia. 2. Perpustakaan dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi

pengajian tinggi. 4. **Sila tandakan (V )

SESI PENGAJIAN: 2007/2008

SULIT (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972)

TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisaslTjadan di mana penyelidikan dijalankan)

V TIDAK TERHAD

(TANDATANGAN PENULIS)

Alamat Tetap:

KG SUNGAILIMAU, IJOK, 34510 BATU KURAU, PERAK.

PROF. MADYA DR. ZAINAL ALAM BIN HARQN (Nama Penyelia)

Tarikh: / »l / p 7 Tarikh:

CATATAN: ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak

berkuasa/organisasi berkenaan dengan menyatakan sekali tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.

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

terms of scope and quality for the award of the degree of

Master of Engineering (Electrical.)

Signature

Name of Supervisor

Date

PM.Dr.ZAMNAL ALAM B.HARON

* > £ N o v O o 0 ^

PARTIAL DISCHARGE DETECTION FOR CONDITION MONITORING OF

AN 11-KV XLPE CABLE

NOR AKMAL BT MOHD JAMAIL

A thesis submitted

In fulfillment of the requirement for the award of the Degree of

Master of Engineering (Electrical)

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

NOVEMBER, 2007

i i i

DEDICATION

This is special dedicated to

my beloved husband,

Qamarul Ezani B. Kamarudin,

my lovely newborn son,

Muhammad Ammar Syafiq,

and my family for their continuous love and prayers,

also to all my friends for their patient, kindness and cooperation .

I wish to thanks all of you for your support during my studies in UTHM.

May God bless all of them.

iv

ACKNOWLEDGEMENT

In the name of Allah S.W.T., the Most Beneficent, the Most Merciful.

Foremost, all praise to Allah for the entire incredible gift endowed upon mc and for

giving me the health and strength to complete this final project.

I am deeply grateful for the help that I received from my supervisor,

Associate Professor Dr. Zainal Alam bin Haron during this development of this

project. His willingness to help and ideas has kept me on my toes from the beginning

stage of this project until the completion of this thesis.

Many thank to P M Tarmidi Tamsir and Mr. Anuar, whom have given me the

convenience to approach all facilities available in the IVAT, UTM.

Special thanks to my lovely husband, Qamarul Ezani B. Kamarudin and my

son, Muhammad Ammar Syafiq for their support and encouragement. Also thanks to

Mrs Zuraidah Ngadiron for her help either directly or indirectly throughout the

preparation of this thesis and this project.

Last but not least, these special thanks go to my parents and family for their

faith and prayers that has enable me to succeed.

V

ABSTRACT

High voltage insulation failure has been a main cause of high voltage systems

for a long time now. It is found that this phenomenon occurs due to the existence of

partial discharge in voids found in insulation of cables, especially XLPE (Cross-

linked polyethylene) cables. Partial discharge normally exists in voids in cables

which are produced accidentally during the extrusion process of cables. However,

improvisation of XLPE cables from one generation to another generation has reduced

voids gradually and thus, reducing the threat of partial discharge. Yet, the effects of

partial discharge could not be underestimated as it would lead to serious breakdown

and electrical apparatus failure. Therefore, partial discharge testing by using a partial

discharge detector is one of the main tests used to determine the quality of the XLPE

cable so that the necessary steps and precautions can be made on the cable if the

cable does not meet the requirements of the test. In this project the insulation

condition of an XLPE cable with different types of artificial defects will be tested for

partial discharge and the results analysed and discussed. The complete procedures for

doing the testing are also described in this thesis.

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A B S T R A K

Kerosakan penebatan voltan tinggi telah menjadi punca utama tcrhadap

sistem voltan tinggi sejak kebelakangan ini. Didapati bahawa fenomcna ini berlaku

disebabkan oleh kewujudan discas separa di dalam ruang atau lubang yang didapati

pada penebatan kabel terutama kabel jenis XLPE (Cross-linkedpolyethylene).Discas

separa kebiasaannya wujud di dalam ruang atau lubang pada penebatan kabel yang

berlaku ketika proses penyemperitan kabel. Walau bagaimanapun, inovasi terhadap

kabel telah berlaku dari satu generasi kepada satu generasi untuk mengurangkan

ruang pada kabel dan seterusnya mengurangkan kejadian discas separa. Sehingga

kini, kesan terhadap discas separa tidak dapat dihapuskan dan ia akan menyebabkan

berlakunya pecah tebat yang serius dan seterusnya berlakunya kerosakan perkakasan

eletrik. Oleh sebab itu, pengujian discas separa dengan menggunakan pengesan

discas separa TE 571 adalah merupakan pengujian yang penting untuk menentukan

tahap kualiti kabel XLPE maka langkah yang sepatutnya diambil terhadap kabel

tersebut boleh dilakukan jika kabel tersebut tidak memenuhi kriteria yang ditetapkan.

Projek ini akan membincangkan tentang keadaan penebat kabel XLPE yang

mempunyai kerosakan buatan yang berbeza berdasarkan kepada pengujian discas

separa dan prosedur yang lengkap untuk melakukan pengujian discas separa

dibincangkan dalam tesis ini.

V I I

TABLE OF CONTENTS

CHAPTER ITEM

SUPERVISOR DECLARATION

TITLE

DECLARATION

DEDICATION

ACKNOWLEDGEMENTS

ABSTRACT

ABSTRAK

CONTENTS

LIST OF TABLE

LIST OF FIGURE

SYMBOLS/TERMS

LIST OF APPENDIX

I INTRODUCTION

1.0 Introduction 1

1.1 Partial Discharge Phenomenon: Terminology 3

1.2 Background of the Problem 4

1.3 Objectives 4

1.4 Project Scopes 5

1.5 Significant Of the Project 5

1.6 Thesis Layout 6

PAGE

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LITERATURE REVIEW

2.0 Partial Discharge Detection

2.1 Gas /Vacuum as Insulator

2.2 Liquid Dielectric

2.3 Solid Dielectric

2.4 Applications of Insulating Materials in Cables

2.4.1 Polymeric Insulation

2.5 Introduction of XLPE Cables

2.5.1 Failure of the Cable

2.6 Partial Discharges

2.6.1 Classification

2.7 Inception of Internal Discharges

2.7.1 Gas-filled Cavities

2.7.2 Inclusions

2.7.3 Oil-filled Cavities

2.8 Inception of Surface Discharges

2.9 Inception of Corona Discharges

2.10 Discharges by Electrical Treeing

2.11 Partial Discharge in Cable

2.12 Insulation System Model

2.13 Parti al Discharge Void Model

2.14 Quantities Related to the Magnitude of Dischargi

2.14.1 Charge transfer

2.14.2 Apparent Charge Transfer in the Sample

2.14.3 Discharge Energy

2.14.4 Dielectric Losses Due to Discharges

2.14.5 Integrated Quantities

2.15 Breakdown Due to Internal Discharges

2.16 Detection Methods

2.16.1 Electrical Detection

2.16.2 Optical Detection

ix

2.16.3 Chemical Detection 26

2.16.4 Acoustic Detection 27

2.17 Partial Discharge Measurement 28

2.17.1 Introduction 28

2.17.2 Discharge Detection Using Straight Detectors 28

2.17.3 Discharge Measurement for Cable 31

2.17.4 Calibration of Discharge Detectors 33

2.17.5 Discharge detection in Power Cable 33

DESCRIPTION OF THE EQUIPMENT AND MATERIALS

3.0 Introduction 36

3.1 System Components 36

3.1.1 TE 571 Detector 36

3.1.2 AKV Coupling Quadripole 37

3.1.3 Special Cable 38

3.1.4 AC Test System Operating Terminal 39

3.1.5 PD Calibrator (KAL 450) 39

3.1.6 Apparatus and Their Function 40

3.2 Mains and Earth Connections 42

3.2.1 Main Connection 42

3.2.2 Earth Connection 43

3.2.3 Computer Connection 43

3.2.4 Instrument Front Panel PD Detector 43

3.2.4.1 Monitor 43

3.2.4.2 Data Memory 44

3.2.4.3 Keyboard 44

3.2.4.4 Mouse Connection 44

3.2.4.5 Front Panel Controls 44

3.3 Connecting the AKV 45

3.3.1 Connections for Standard Use 45

3.3.2 Connection for Use with Additional Secondary Unit 46

3.3.3 Current Range Selection 46

3.4 Operation 46

3.4.1 TE571-OSW Office software introduction 47

3.4.2 PD-Scope™ 48

3.4.3 Functions of Key Fl-F 10 49

3.4.3.1 Help 49

3.4.3.2 Config 49

3.4.3.3 Calibration 50

3.4.3.4 Main Menu 50

3.3.4.5 Pause 53

3.3.4.6 F6~PD Units 53

3.3.4.7 Windows 54

3.3.4.8 Auto Record 54

3.3.4.9 Manual Record 55

3.3.4.10 Print 55

3.4 Test Circuit Construction 56

METHODOLOGY

4.0 Introduction 57

4.1 Preparation Prior to Perform the Testing 5 8

4.1.1 Safety Precautions 59

4.2 Launching the Display of TE 571 Detector 60

4.3 Partial Discharge Level Calibration 61

4.4 Voltage Calibration 63

4.5 Test Procedures 65

4.6 Testing Circuit Arrangement 68

xi

Insulation

5.1.2.7 PD Level Corresponding to Injected 86

Voltage

5.3 Summary 89

VI CONCLUSIONS AND RECOMMENDATIONS

6.0 Conclusions 90

6.1 Recommendations 91

REFERENCES 92

APPENDICES 95

69

70

70

74

75

77

79

81

V RESULTS & DISCUSSION

5.0 Introduction

5.1 Testing Results

5.1.1 Calibration results

5.1.2 Cable Testing and Measurement Results

5.1.2.1 Case A: Cable in Good Condition of

Insulation

5.1.2.2 Case B: Void between Cable Insulation

and Iron

5.1.2.3 Case C: Void between Cable Insulation

and Aluminium

5.1.2.4 Case D: Void between Cable Insulation

and Copper

5.1.2.5 Case E: Olive Oil Effect on the Test Cable 83

Insulation

5.1.2.6 Case F: Grease Oil Effect on the Test Cable 84

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LIST OF TABLE

NO. OF TABLE TITLE

2.1 Cable insulation 11

2.2 Insulation and technology of H V cables 12

3.1 Electrical apparatus and their function 40

xiii

LIST OF FIGURE

NO. OF FIGURE TITLE PA

2.1 Corona at sharp edges (opposite electrodes at a 17

fair distance)

2.2 Simplified insulation model and model for an electronic 19

attenuator

2.3 Simplified partial discharge void model with internal 20

resistive leg

2.4 Electrical discharge in a cavity and its equivalent circuit 24

2.5 Sequence of cavity breakdown under alternating voltages 24

2.6 Straight discharge detection circuit 29

2.7 Partial Discharge patterns 31

2.8 Equivalent circuit of the cable for discharges 32

2.9 Discharge detector connection to long length of cable 32

2.10 Partial discharge testing arrangement for distributed 35

parameter equipment (cables, transformer windings, etc)

3.1 Partial Discharge Detector 37

3.2 AKV Coupling Quadripole 38

3.3 System component-AKV 573 Coupling Quadripole 38

3.4 AC test system operating terminal 39

3.5 Partial discharge calibrator (KAL 450) 40

3.6 High voltage transformer 41

3.7 Resonant high voltage transformer and HAEFELY 41

coupling capacitor

3.8 AKV 573 connections 45

3.9 PD Scope with ellipse 48

3.10 Main menu display 50 3.11 Typical PD Test Circuit Arrangement 56 4.1 The Flow Chart of the project 58 4.2 The display of configuration for F2 key 60 4.3 Block diagram of PD level calibration 61 4.4 PD calibration menu 62 4.5 PD Scope display after PD level calibration success 63 4.6 Block diagram of voltage calibration 63 4.7 PD Scope display after PD level and voltage calibration 65

success

4.8 Display of test identification 66

4.9 Auto Record display that displays the information about 67 the user

4.10 The partial discharge test circuit arrangement 68

5.1 Partial Discharge Detector 69

5.2 The Arrangement of 1 lkV XLPE Cable 70

5.3 PD Scope display before calibration is done 71

5.4 Display of PD level and voltage calibration 72

5.5 Display of PD level calibration was success 72

5.6 Display of sinusoidal wave when the high voltage is 73

injected to the Partial Discharge Detector TE 571

5.7 Display of PD level and voltage calibration were success 73

5.8 PD Scope display for cable in good condition of insulation 76

5.9 Line diagram for testing the cable in good condition of 77

insulation

5.10 PD Scope display for void between cable insulation and 78

iron

5.11 Line diagram for void between cable insulation and iron 79

5.12 PD Scope display for void between cable insulation and 80

aluminium

5.13 Line diagram for void between cable insulation and 80

aluminium

5.14 PD Scope display for void between cable insulation and 81

copper

5.15 Line diagram for void between cable insulation and 82

copper

5.16 PD Scope display for olive oil effect on the test cable 83

insulation

5.17 Line diagram for olive oil effect on the test cable insulation 84

5.18 PD Scope display for grease oil effect on the test cable 85

insulation

5.19 Line diagram for grease oil effect on the test cable 85

insulation

5.20 PD values and cable performance of XLPE cable 88

according to different voltages

5.21 PD values and cable performance of XLPE cable 89

according to different voltages

LIST OF ACRONYMS/SYMBOLS/TERMS

Partial Discharge

High Voltage

Cross-linked polyethelyne cable

Kilo Volt

Sulphur Hexafluoride

International Electrotechnical Commission

Universiti Teknologi Malaysia

Polyvinyl Chloride

Polyethylene

Ethylene-propylene

Pico Coulomb

Nano Coulomb

MegaHertz

Dissolved gas analysis

High performance liquid chromatography

Kilo

Cable transit time

relative permittivity of the dielectric

Coupling quadripole

Mega

Frequency

xvii

LIST OF APPENDICES

APPENDIX ITEM PAGE

A FIGURES OF THE SETTING EQUIPMENT 95

B TABLE OF THE RESULTS 97

CHAPTER I

INTRODUCTION

1.0 Introduction

Partial discharge detection is nowadays a very well established method for

monitoring the insulation condition of an electrical apparatus. The breakdown of

insulation while in service can cause considerable damage to an apparatus and to the

system to which it is connected. It has been recognized that failures of this type often

may be related to the occurrence and severity of partial discharges within voids

and/or on the surface of the insulation. Testing of high voltage apparatus for partial

discharges has long been recognized as an important part of quality control for these

devices [1].

Partial discharge, as implied by its name, is a type of localized discharge

resulting from transient gaseous ionization in an insulation system when the voltage

stress exceeds a critical value. The ionization is localized over only a portion of the

distance between the electrodes of the system. The resultant partial discharge signals

appear as very small magnitude, fast rise pulse (10-100ns) with irregular waveshapes.

Partial discharges do not cause complete breakdown of the dielectric [2].

In practice, four types of partial discharge may be identified; they are,

namely, Internal Discharge, Surface Discharge, Corona Discharge and discharge in

electrical trees [13]. In insulation systems with strongly inhomogeneous field

2

configurations or inhomogeneous dielectrics, the breakdown field strength can be

locally exceeded without complete breakdown occurring within a short time. Under

this condition of incomplete breakdown the insulation between the electrodes is only

partially bridged by discharges. These partial discharges have considerable practical

significance particularly for the case of stress by alternating voltages. Partial

discharges cause deterioration of insulation materials and are a primary cause of

insulation failure at moderate and high voltages especially due to surface or internal

discharges or treeing. The electric strength of solid insulation may decrease greatly

with time of voltage application if discharge occurs within gaseous inclusions, at

sharp-edged conductors embedded in the solid and as a result of surface

contamination.

Partial discharge measurement is a very well known method for assessing the

quality of an insulation system of high voltage devices, because the life of high

voltage equipment depends on the presence of partial discharge. The aim is to detect

the initial destruction in the electrical insulation as a result of electrical stress. The

presence of a multiplicity of different partial discharge sources and their appearance

shows different physical and electrical characteristics. For the economic use of high

voltage operational equipment, it is necessary to always know the condition of the

equipment in service. That is the reasons why monitoring, analysis or diagnosis

become a fixed part in power generating, transmission and distribution systems. In

this area the partial discharge measurement is an important diagnostic tool.

A Partial Discharge (PD) measurement is used as one of the quality control

test for extruded cables in the medium and high voltage range. The normal situation

would be that partial discharges would not occur in such cables when energized to

stresses usually required in specification. Occasionally, however, there will be an

isolated defect which does produce PD [14].

Cables constitute one very important electrical apparatus for transmission of

electrical energy by underground means. Large power transmission cables are of

importance and hence testing of power cables is considered a must. Partial discharge

measurement and the discharge locations are important for cables, since the life of

3

the insulation at a given voltage stress depends on the internal discharge. Also the

weakness of the insulation or faults can be detected with the help of this test.

For maintenance purposes, early detection of discharges in cables is an

important diagnostic tool to assess the cable condition and if possible to locate the

defect, especially since it highly undesirable to have to remove the cables from the

operation even for occasional Partial Discharge testing.

A point of significant practical implication is the fact that surge propagation

in the cable is affected by attenuation as well as wave shape deformation. This fact is

fully exploited in the partial detection method as the principal means for detecting

and locating partial discharge occurrences in cables. Progress in cable insulation

design, such as the inclusion of semiconducting layers to give a uniform electric field

distribution, and hence result in less partial discharge occurrences and a better over

voltage control, on the downside causes more significant PD signal deformation

during propagation. Since an XLPE cable's insulation is very sensitive to partial

discharges occurring within itself, fast PD detection by online monitoring is essential,

and therefore a detectable signal is needed to be picked up at the monitoring

terminals.

1.1 Partial Discharge Phenomenon: Terminology

Partial discharge is an electrical discharge that only partially bridges the

dielectric or insulating medium between conductors. Examples are: internal

discharges, surface discharges and corona discharges. Internal discharges are

discharges in cavities or voids which lie inside the volume of the dielectric or at the

edges of conducting inclusions in a solid or liquid insulating medium. Surface

discharges are discharges from the conductor into a gas or a liquid medium and form

on the surface of the solid insulation not covered by the conductor. Corona is a

discharge in a gas or liquid insulation around the conductors that are away or

removed from the solid insulation [11].

1.2 Background of the Problem

4

Testing of high voltage apparatus for partial discharge is an important part of

quality control. Weak points in an insulation like voids, cracks and other

imperfections lead to internal or intermittent discharges in the insulation. These

imperfections being small are not revealed in capacitance measurements but are

revealed as a power loss component. Partial discharge in voids may cause

deterioration of solid insulation materials. They often start in voids enclosed in the

insulation or at the interface defect. Partial discharge is a major source of insulation

failure in a cable. The accurate location of the discharge is of crucial importance in

on-site maintenance and repair. This project will concentrate on partial discharge

detection to determine the insulation condition of the cable.

1.3 Objectives

The objectives of this project are:

i. To prepare the complete test procedures for partial discharge detection of

XLPE cables by using the PD detector, TE 571.

ii. To test the condition of cable by the method of partial discharge detection.

iii. To detect the partial discharge of cable for assessing the likelihood of a

fault on a cable containing an incipient defect.

iv. To study the partial discharge patterns and to interpret the condition of the

cable with different types of artificial defects.