modeling of water tree degradation in...

MODELING OF WATER TREE DEGRADATION IN UNDERGROUND

POLYMERIC POWER CABLE USING TIME DOMAIN REFLECTOMETRY

METHOD

AZNIZA BINTI AHMAD

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical – Power)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JANUARY 2015

iii

Dedicated to my beloved parents

Ahmad bin Mahmood & Robiah binti Rojali

Siblings

Azizah binti Ahmad

Nazri bin Ahmad

Azida binti Ahmad

Nasir bin Ahmad

and

All my friends

for their support and encouragement

iv

ACKNOWLEDGEMENT

With the name of ALLAH, Most Generous and Most Merciful

The author wishes to take this opportunity to greatest gratitude and special

thanks to the final year master project supervisor Dr Yanuar Z Arief, for her

guidance, assistance, patience and time spent throughout the process of completing

this Final Year Master Project. Valuable advice, her kindness to share her knowledge

had been a great help to the author in the completion this final year master project

application, research and report. Others attitude from critique, helping the author,

share the experience, share the knowledge and many more is much appreciated.

Besides that, the author would also like to greatest and special thanks you to

the assessor Assoc. Prof. Dr Mohamed Afendi bin Mohamed Piah and Dr Mohd

Hafizi for her reviews, ideas, critic and comments. All the information that her give

is very helpful to the author in order for the author to further improve and enhance

the final year master project application and report.

Apart from that, also would like to thank you to parents for the support and

guidance throughout all the process of completing this Final Year Master Project.

The author also takes the opportunity to thank you to all lecturers and friends

who had also been very supportive and a great help to share their valuable ideas and

experience either directly or indirectly.

Author

January, 2015.

v

ABSTRACT

Cross-linked polyethylene (XLPE) is a one of the insulation materials in

polymeric power cable. They are usually used in underground medium voltage

cables. These cables are exposed to a significant risk of premature ageing and failure

of polymeric cable. One of that phenomenons is water treeing. In this project, water

tree has been modeled using MATLAB simulation while PSpice software was

regarded as an experimental model. Time domain reflectomerty (TDR) is applied as

a method to investigate the degradation and location due to the water tree. Five

different geometries of cables with varied in two different length will be measured in

this study. The simulation results show the wave propagation characteristics such as

attenuation and velocity are important parameters as a benchmark to analyze the

signals generated from PSpice software. Moreover, in experimental model shows

that the water tree can be defined by implemented the TDR method. It was found that

the error percentage of simulation results and calculations is 9.06%.

.

vi

ABSTRAK

Polietilen Hubung-Silang (XLPE) adalah salah satu daripada bahan penebat

dalam polimer kabel. Ianya biasa digunakan dalam kabel bawah tanah bagi voltan

sederhana. Kabel ini terdedah kepada risiko penumbuhan pra-matang dan kegagalan

kabel polimer. Pepohon air merupakan salah satu fenomena ini. Dalam kajian ini,

pepohon air dimodelkan dengan menggunakan simulasi MATLAB manakala

perisian Pspice sebagai eksperiment kajian. Oleh itu, ‘Time Domain

Reflectomerty’(TDR) adalah kaedah untuk menyiasat degradasi dan lokasi pepohon

air itu. Kajian ini diukur dengan menguji lima perbezaan geometri serta dua ukuran

yang berbeza. Hasil simulasi, menunjukkan ciri-ciri perambatan gelombang seperti

pengecilan dan halaju adalah parameter adalah penting sebagai penanda aras untuk

menganalisis isyarat yang dihasilkan dari perisian Pspice. Selain itu, keputusan

eksperimen menunjukkan, pepohon air boleh dilaksanakan dengan kaedah TDR.

Peratusan kesilapan bagi hasil simulasi eksperiment dan pengiran ialah 9.06 %.

.

vii

TABLE OF CONTENTS

CHAPTER CONTENT PAG

E

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xv

LIST OF SYMBOLS xvi

LIST OF APPENDICES xvii

1 INTRODUCTION

1.1 Overview 1

1.2 Problem Statement 3

1.3 Objective of the Project 3

1.4 Scope of the Project 3

1.5

1.6

Development Software

Outline of thesis

4

4

2 LITERATURE REVIEW

2.1 Background Study 6

2.2 Recent Literature on Water Treeing 6

2.3 Crosslinked Polyethylene (XLPE) Polymeric 8

viii

Cables

2.4 Transmission Line 10

2.5 Water Tree In Polymeric Cable 12

2.6 Time Domain Reflectometry (TDR) 14

3 METHODOLOGY

3.1 XLPE Cable Geometry 18

3.2 Modeling using MATLAB simulation 21

3.2.1 Wave propagation characteristics 30

3.3 Modeling using PSpice simulation 32

4 RESULTS AND DISCUSSIONS

4.1 Introduction 38

4.2 MATLAB Simulation Result and Analysis 39

4.3 Ideal/Unaged Cable Condition for Five Cable

Difference Geometry

45

4.4 PSpice Simulation Result and Analysis for

100m Length of Cable 1

49

4.4.1 Unaged Cable Condition 49

4.4.2 Degrade cable condition 51

4.5 PSpice Simulation Result and Analysis for 25m

length of cable 3

59

4.5.1 Ideal/Unaged cable condition 59

4.5.2 Degrade cable condition 62

4.6 Result for cable 1,2,3,4 and 5 with difference

length and condition

69

4.6.1 Cable 1 Unaged –Degraded condition 69




ix


5 CONCLUSION AND RECOMMENDATIONS

5.1 Overview 84

5.2 Conclusion 84

5.2 Recommendations 86

REFERENCES 87

APPENDIX A-C 90-104

x

LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 TNB cable parameter 19

3.2 Characteristics Impedance , for five cables

geometry in ohm(Ω)

29

3.3 Time delay of coaxial cable and test cable for

100m length

32

3.4 Time delay of coaxial cable and test cable for

25m length

32

xi

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Diagram of underground cable failure reported

by Tenaga Nasional Berhad during 1

September 2010 – 31 August 2011

2

2.1 Molecular structure for polyethylene and

XLPE

8

2.2 Single Core XLPE Polymeric power cable 9

2.3 Typical XLPE Cable Geometry 9

2.4 Equivalent circuit for two port networks 10

2.5 The microscope observation of the water tree

channel

12

2.6 Water Trees Growing from the Inner (bottom)

and Outer (top) Semiconductive Screens

13

2.7 Vented water trees in power cable insulation 13

2.8 Functional block for a time domain

measurement set-up

15



3.3 Unaged XLPE Cable Model 21

3.4 Degraded XLPE Cable Model 21

3.5 XLPE insulation degraded due the water tree 23

3.6 Flowchart of MATLAB program to

characteristics impedance,

25

xii

3.7 Characteristics Impedance, versus Frequency, Hz 26

3.8 Characteristics Impedance, versus Frequency, Hz

for Cable 1

26


for Cable 2

27


for Cable 3

27


for Cable 4

28


for Cable 5

28

3.13 Flowchart of MATLAB program to attenuation

propagation and speed velocity

30

3.14 Cross section of partially degraded XLPE cable

with two insulation region

31

3.15 Functional block diagram for TDR system 34

3.16 TDR system Circuit Model 34

3.17 PSpice modeling for unaged cable condition 35

3.18 PSpice modeling for degraded cable condition 35

4.1 Attenuation dB/m versus Frequency, Hz for ideal

cable condition of five difference cable geometry

38

4.2 Velocity (m/s) versus Frequency, Hz of ideal cable

condition for five difference cable geometry

38

4.3 Attenuation (dB/m) versus Frequency Hz for cable 1 40



4.6 Velocity (m/s) versus Frequency Hz for cable 2 41



xiii





4.13 Attenuation dB/m versus cable Velocity m/s versus

cable

43

4.14 Velocity m/s versus cable 44

4.15 Voltage,V versus time,s of reflection pulse for five

different geometry cable

45

4.16 Signal for result for unaged cable condition in figure

4.16

45

4.17 Voltage,V versus time,s of reflection pulse for

unaged cable condition in cable 1

48

4.18 Voltage, V versus time, s of 25% degraded cable 1

at ideal /degraded (50m/50m) length

50

4.19 Signal result for degraded cable condition 50



52



53

4.22 Unaged and Unaged–Degraded reflected signal for

test cable length 100m,50m/50m,25m/75m and

25m/75m of 25% degraded condition

54

4.23 Voltage, V versus time, s of 5%,25%, 50% and 75%

degraded cable 1 at ideal /degraded (50m/50m)

length

57

4.24 Voltage,V versus time,s of reflection pulse for cable

3

58


at ideal /degraded (12.5m/12.5m) length

61

xiv



63



64

4.29 Voltage, V versus time, for cable 1 68



\4.32 Voltage, V versus time, for cable 2 71












xv

LIST OF ABBREVIATIONS

XLPE - Crosslink polyethylene

PE - Polyethylene

PD - Partial discharge

PVC - Polyvinyl Chloride

SR Silicon rubber

TDR - Time Domain Reflectometry

FFTs - fast Fourier transforms

RF - Radio frequency

GFCI - Ground Fault Current Interrupter

TD - Time delay

xvi

LIST OF SYMBOLS

H/m - Hendry per meter

Ω/m - Ohm per meter

µs - Micro per second

S/m - Simon per meter

F/m - Farad per Meter

Zo - Characteristics impedance

ns - Nano second

us - Micro second

Vi - Voltage incident

Vr - Voltage reflection

Attenuation

β(ω) Phase velocity

ɛ Permittivity

µ Permeability

c Velocity

Length

xvii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Gant chart project 53

B MATLAB coding for characteristics impedance 90

C MATLAB coding for wave propagation characteristics 103

CHAPTER 1

INTRODUCTION

1.1 Overview

Polymeric cables are commonly used in power system application as cable

insulation, such as XLPE, PE, PVC, SR and other. In economical perspective, it is

reported that there is significantly reduction demand of paper-type cable and

increasing of polymeric ones. The introduction of polyethylene (PE) extruded cables

into the power distribution sector in the early 1950s required a rapid development of

partial discharge (PD) detection technique and testing standards to assess the

reliability of these cables.

One of the polyethylene insulation materials is a crosslink polyethylene

(XLPE) which is widely used as insulation material in power cable. XLPE cable

provides the low dielectric losses. However, after the put into the service, the cable

will be affected caused by the surrounding factor. In order to ensure the quality of

power supplies the aging status installed the cable. One of the primary causes of

aging breakdown will be traced in year 1972 due to moisture ingression into the

insulation is water treeing[1]. Water trees from and convert to electrical trees and le

2

ad to water trees. Water tree leads to decreased insulation resistance an increased in

leakage current[2].

A fundamental interest of power utilities is to increase the total reliability at a

minimum cost by improved maintenance routines. Diagnostic testing of installed

XLPE power cables is of high interest because of the large number of old cables in

service with high probability of failure caused by water tree degradation[3].

Tenaga Nasional Berhad (TNB); a power utility company in Malaysia

reported that during 1 September 2010 – 31 August 2011, statistically there is a

failure of underground cable (medium voltage, 6.6 kV) due to water tree/water

ingress is about 16.5% which occurred in Selangor territory[2].

Figure 1.1 Diagram of underground cable failure reported by Tenaga

Nasional Berhad during 1 September 2010 – 31 August 2011

Therefore, this paper attempts to model the water tree degradation in

underground polymeric cable and analyse the data using time domain reflectometry

(TDR) as the proposed method for the detection mechanism.

17%

30% 53%

Failure of underground cable (medium voltage, 6.6

kV)reported by Tenaga Nasional Berhad during 1 September

2010 – 31 August 2011

Water interes

Insulation failed

Other (cable termination,core

opend,damanged,straight

through join)

3

1.2 Problem Statement

Water tree is one of the major causes of premature ageing and failure of

extruded medium voltage of polymeric cables which do not have water-impervious

barriers. Besides technological efforts, it has been a challenge up to now to

overcome such failures by improved insulating compound, mainly on the basis of the

chemically crosslinked low density polyethylene (XLPE).

Consequently, a need for investigating of water tree has arisen, and thus

reduces the need of cable testing to compare and preselect materials. The detection

and mechanism of water tree in polymeric cable is not clearly understood yet

1.3 Objective of Project

The objective of this project is to model water tree degradation in

underground polymeric cable. The degradation and location of water tree in

underground polymeric cable using TDR concept is also analysed.

1.4 Scope of Project

In order to achieve the objective of the project, there are several scopes that

have been outlined which are:

i. The five type of 6.6kV XLPE cable will be investigated

4

ii. The test cable varied in two different length that is 25m and 100m

length

iii. The test cable divided two part that is ideal/unaged cable XLPE and

degraded XLPE

iv. Time Domain Reflectometry (TDR) method is applied to analyze the

signal and detect the water tree mechanism

v. This project only involves simulation using MATLAB software to be

model polymeric cable and the experimental set-up developed using

PSpice circuit simulation

1.5 Development Software

This project uses two types of software which are:

i. MATLAB R2010a

For simulation to get the wave propagation characteristic of the ideal

cable and degraded cable.

ii. PSpice

For experimental set up to detect water tree degradation and location

using applies time domain reflectometry (TDR) method.

1.5 Outline of Thesis

This thesis consists of five chapters. The first chapter introduces the

background of the project, the problem statement, the objective, and the development

5

software of this project. The second chapter will be discussed about the literature

reviews that are related to the study.

Chapter 3 will explore the methodology to realize this project. Then, chapter

4 will discuss the result and discussion of overall project. Last but not least, the

conclusion and recommendation will be summarized in Chapter 5.

87

REFERENCE

1. Kuan, T.M., et al. Wave propagation characteristics of polymeric

underground cables. in 2011 5th International Power Engineering and

Optimization Conference, PEOCO 2011 - Program and Abstracts. 2011.

2. Y. Z. Arief, M.S., Z. Adzis, M. Z. H. Makmud Degradation of Polymeric

Power Cable due to WaterTreeing under AC and DC Stress. 2012 IEEE

International Conference on Power and Energy (PECon)Kota Kinabalu

Sabah, Malaysia, 2-5 December 2012.

3. M. Ahmed, M.A.A.-O., M. A. Garwan, K. Y. Shoufi, Z. M. Hamouz, How

Good are Electrical Diagnostic Tests to Predict Water Trees In HV Cables –

An Evaluation Using Optical Microscopy. Journal of Electrical Engineering,

2005. vol. 56: p. pp-31- 35.

4. Eriksson, G.M.a.R., High frequency characteristics of a shielded medium

voltage XLPE cable. Annual Report Conference on Electrical Insulation and

Dielectric Phenomena, 2001

5. Ariffin, A.M., et al. Application of time domain reflectometry technique in

detecting water tree degradation within polymeric-insulated cable. in

Condition Monitoring and Diagnosis (CMD), 2012 International Conference

on. 2012.

6. Tze Mei, K., A.M. Ariffin, and S. Sulaiman. Signal analysis to detect water

tree location in polymeric underground cables. in Research and Development

(SCOReD), 2011 IEEE Student Conference on. 2011.

7. Hashmi, G.M., R. Papazyan, and M. Lehtonen. Determining wave

propagation characteristics of MV XLPE power cable using time domain

reflectometry technique. in Electrical and Electronics Engineering, 2009.

ELECO 2009. International Conference on. 2009.

8. A. Giovanni Gonzalez, I.P., Richard M White, Paul K. Wright, Novel Onlin

RF technique for Detection of Water Trees in Underground Powered

Distribution Cables. 2011 Electrical Insulation Conference,

Annapolis,Maryland, 5 to 8 June 2011.

9. Berhad, U.C.M., XLPE Insulated Power Cables, in Leader 1976.

88

10. Dubickas, V., On-Line Time Domain Reectometry Diagnostics Of Medium

Voltage XLPE Power Cables, in Licentiate Thesis Stockholm. Sweden 2006,

Royal Institute of Technology.

11. Indiamart. Nicco Corporation Limited. 1996-2014.

12. Division, T.D., Underground Cable System Design Manual June 2012 Asset

Management Department. 2012.

13. Note, L., Transmission Line. 2014.

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frequency wave propagation characteristics in medium voltage XLPE cable

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15. E. F. Steenis, F.H.K., Water treeing in polyethylene cables. IEEE

Transactions on Electrical Insulation, October 1990. Vol. 25, No. 5, pp. 989-

1028.

16. Papazyan, R., Techniques for localization of insulation degradation along

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(KTH), Stockholm, Sweden.

17. Kai Zhou, W.Z.a.X.T., Toward Understanding the Relationship between

Insulation Recovery and Micro Structure in Water Tree Degraded XLPE

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18. Atkinson, J.M. TDR Tutorial - Introduction to Time Domain Reflectometry.

Copyright ©2002, Granite Island Group.

19. Dyer, S.A., Survey of instrumentation and measurement, N.Y.W.

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