i

TITLE

ELECTRIC FIELD AND SPACE CHARGE CHARACTERISTICS OF XLPE

INSULATION DOPED WITH NANOFILLERS

JAMIL BIN SHAARI

A project report submitted in partial

fulfilment of the requirement for the award of the

Degree of Master of Electrical Engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

JANUARY 2018

iv

DEDICATION

A special thankfully dedication to,

My beloved other half,my wife Siti Asma Binti Muhammad Suhami for her

delicately tenderness, warmth support and invaluable effort

My children Ali Hanbali, Uthman Maliki and Rayda Rhumaisa for their

patience,lovely smile and cheefulness

Thank for all of your quality time and supportive help

Also not to forget to all my supervisor, lecturers and colleagues for their kindness in

this educational journey

v

ACKNOWLEDGEMENT

In the name of Allah the Most Gracious and the Most Merciful

Alhamdulliah, a heartfully and most thanks to Allah upon His blessing and His

mercy and also peace and bless onto His Prophet Muhammad. Finally, I was able to

complete my master’s project as well as finishing my master degree course. This

master’s report has represented the symbol of an idea being constantly poured,

spiritually and emotionally supportive action and guidance from my family, lecturers

and colleagues.

I would like to express my heartily and honestly gratitude towards my master’s

project supervisor Dr Nor Akmal Binti Mohd Jamail, for unwaveringly enthusiasm

and brilliantly idea that advising and assisting me throughout the step by step process

of preparing this project completely. I truly honoured to be under her guidance and

supportively assistance.

Secondly, my deepest appreciation to all my family members for their tolerant

and cooperation that support me all the time. To my lovely wife Siti Asma Binti

Muhammad Suhaimi, a special thank reserved to her for her kindness, motivation and

most of all, an honestly and warmth smile in wholeheartedly entertaining my

mischievous manners.

Not to forget to all my colleagues, many thanks to them for their sincere

helping hand either directly or indirectly in finishing my master project.

vi

ABSTRACT

Various types of nanoparticles had been introduced as additive to polymeric

insulator by previous researchers. As a result, the existence of nanometre-size particles

is well acknowledged in enhancing the dielectric strength in insulation material. The

remained unanswered that is concerning the nanometre-sizes in maximising the

potential of nanocomposite insulator. The main criteria to dictate the dielectric

performance is by measuring the level of electric field distribution. While, electric

field properties also influenced by the accumulation amount of space charge. So, this

study was conducted to evaluate the electric field and space charge distribution in

within nanocomposite insulator. The primary purpose is to identify the finest size in

each type of selected nanoparticles in optimising the dielectric properties, but selecting

the best type of nanofillers as well. Three different sizes attributed from 100nm, 80nm

and 50nm were selected from three different nanofillers which are nanometre silicon

dioxide (NSD), nanometre titanium dioxide (NTD) and air. All these nanofillers were

doped in XLPE separately for simulation based study. Electric field distribution and

space charge tabulation on each selected size were measured and compared.

Consequently, each type of nanofillers give a selection different of sizes for the best

dielectric performance. Conclusively, the best size for NSD, NTD and air were 100nm,

80nm and 50nm respectively. The dominant influence of nanometre-size is the

intrinsic behaviour of an oxidised element in nanofillers. In term of type, NTD is

performed in electric field distribution can correlated with its permittivity constant, ε.

But for space charge tabulation, NSD is better due its intrinsic behaviour and insulation

structure.

vii

ABSTRAK

Pelbagai jenis zarah pada saiz nanometer telah diperkenalkan oleh penyelidik

terdahulu sebagai bahan tambahan kepada penebat polimer. Hasilnya, kewujudan

zarah pada saiz nanometer telah diiktiraf dalam membantu meningkatkan keupayaan

dielektrik dalam bahan penebatan. Namun persoalan yang masih belum terjawab

adalah pada saiz nanometer apakah yang dapat mengmaksimakan potensi penebat

komposit nano. Jika dilihat kembali, kriteria utama dalam menentukan nilai prestasi

dielektrik adalah dengan mengukur tahap taburan medan elektrik. Manakala, medan

elektrik pula turut dipengaruhi dengan nilai kuantiti caj ruang yang terkumpul. Maka,

kajian ini telah dijalankan untuk menilai taburan medan elektrik dan caj ruang yang

terkandung dalam penebat komposit nano. Tujuan utama adalah untuk mengenalpasti

saiz terbaik dalam mengoptimakan kekuatan dielektrik dalam kalangan jenis-jenis

pengisi nanometer yang dipilih. Selain itu juga, tujuannya adalah untuk medapatkan

jenis bahan yang terbaik untuk pengisi nano. Tiga jenis saiz telah dipilih terdiri

daripada 100nm, 80nm dan juga 50nm. Saiz ini dipilih ini pula terdiri daripada tiga

jenis pengisi nano yang berbeza iaitu silikon dioksida (NSD), titanium dioksida (NTD)

dan udara. Kesemua jenis pengisi nano ini dimasukkan ke dalam XLPE secara

berasingan untuk simulasi kajian. Kemudian, taburan medan elektrik dan tabulasi caj

ruang dalam setiap saiz diukur dan dibandingkan. Keputusannya, setiap jenis pengisi

nano memberikan saiz yang beza-beza untuk mengoptimumkan keupayaan dielektrik.

Saiz terbaik untuk NSD, NTD dan udara adalah 100nm, 80nm dan 50nm masing-

masing. Pengaruh yang mendominasi dalam saiz nanometer ialah sifat dalaman

elemen-elemen yang teroksida. Namun, dari segi jenis, NTD menunjukkan prestasi

yang baik dalam taburan medan elektrik yang mana boleh dikaitkan dengan pemalar

ketelusannya,ε. Tetapi berbeza dengan tabulasi caj ruang, NSD adalah lebih baik

disebabkan sifat-sifat dalama dan juga struktur penebatannya.

viii

TABLE OF CONTENTS

TITLE i

DECLARATION ii

DEDICATION iv

ACKNOWLEDGEMENT v

ABSTRACT vi

TABLE OF CONTENTS viii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOL AND ABBREVIATION xiii

CHAPTER 1 INTRODUCTION 1

1.1 Project Overview 1

1.2 Problem Statements 2

1.3 Objectives 3

1.4 Project Scope 3

1.6 Thesis Organisation 4

CHAPTER 2 LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Cross-linked Polyethylene, XLPE 6

2.3 Nanofillers 7

2.3.1 Silicon Dioxide 8

2.3.2 Titanium Dioxide 10

ix

2.3.3 Air 12

2.4 Electric Field 13

2.5 Space Charge 15

2.6 COMSOL Multiphysics Simulation Software 20

2.7 Summary 22

CHAPTER 3 METHODOLOGY 23

3.1 Introduction 23

3.2 Project analysis of HVDC Cables 23

3.3 Procedure of Designing a Model 25

3.4 Summary 34

CHAPTER 4 RESULT AND DISCUSSION 35

4.1 XLPE Nanocomposite Insulation Model 35

4.2 Electric Field Analysis 37

4.3 Space Charge Analysis 49

4.4 Summary 61

CHAPTER 5 CONCLUSION 63

5.1 Conclusion 63

5.2 Summary of the Original Contribution 64

5.3 Recommendations 64

REFERENCES 66

x

LIST OF TABLES

2.1 Comparison of Polyethylene and Cross-linked Polyethylene (XLPE)

properties 6

2.2 Type of space charge formation patterm 17

2.3 Sequence of COMSOL Multiphysics usage for measurement. 22

3.1 Parameters used for XLPE insulator drawing for preliminary result 29

3.2 Relative permittivity of material in this project 29

4.1 Coloured contour and line graph of an XLPE doped with NSD in

different sizes. 40

4.2 Coloured contour and line graph of an XLPE doped with NTD in

different sizes. 43

4.3 Coloured contour and line graph of an XLPE filled with air in

different nanometre-sizes. 46

4.4 Coloured contour and line graph of an XLPE doped with NSD in

different sizes. 53

4.5 Comparison of space charge tabulation in XLPE doped with NSD

with different sizes 54

4.6 Coloured contour and line graph of an XLPE doped with NTD in

different sizes. 55

4.7 Comparison of space charge tabulation in XLPE doped with NTD in

different sizes 57

4.8 Coloured contour and line graph of an XLPE filled with air in

different sizes. 58

4.9 Comparison of space charge tabulation in XLPE filed with nanosize

of air in different sizes 60

4.10 Comparison of electric field with different type of nanofillers 61

xi

LIST OF FIGURES

2.1 Timeline of research on insulation materials with nanosilica doping. 10

2.2 Electric field line of positive and negative charges 13

2.3 Space charge region between a conductor and an insulator 16

3.1 Project methodology flow chart 24

3.2 Flow chart of model designing procedure in COMSOL Multiphysics 25

3.3 Creating Problem graphic user interface (GUI) 26

3.4 Dimension of the Model selection 26

3.5 Physics specification GUI. 27

3.6 Study selection GUI 27

3.7 Buttons on drawing toolbar 28

3.8 “Array” tools under “Transform” button 28

3.9 Initial model of XLPE insulator with 0.1mm thickness. 29

3.10 Add material window. 30

3.11 Material Tab for defining material properties. 31

3.12 Electrostatics selection within “Boundaries” 32

3.13 Highlighted blue domain for core at 6.6kV 32

3.14 Highlighted blue line of boundary for electric ground, 0V. 32

3.15 Geometry model fill in with meshes. 33

3.16 “Compute” icon for solving the study problem. 33

3.17 Default study for “Electrostatics” module. 34

4.1 3D view of simulated XLPE nanocomposite model. 36

4.2 Half-top view of XLPE nanocomposite model with red dashed line. 36

4.3 Half -front view at the red dashed line cross section from Figure 4.2. 37

4.4 Image enlargement on nanofillers dispersion within XLPE of red box

area from Figure 4.3. 37

4.5 Electric field tabulation in typical XLPE cross sectional area. 38

xii

4.6 Line graph for electric distribution on standard XLPE 38

4.7 Enlargemnet image of electric field distribution in XLPE insulation

doped with different sizes of NSD from 1.2499mm to 1.2515mm 42

4.8 Enlargemnet image of electric field distribution in XLPE insulation

doped with different sizes of NTD from 1.2499mm to 1.2515mm. 45

4.9 Enlargemnet image of electric field distribution in XLPE insulation

filled with different sizes of air from 1.2499mm to 1.2515mm. 47

4.10 Enlargement image of electric field distribution in XLPE filled with

different type of nanofillers from 1.2499mm to 1.2515mm. 49

4.11 Space charge density tabulation in typical XLPE cross sectional area. 50

4.12 Line graph of space charge on typical XLPE insulator 51

xiii

LIST OF SYMBOL AND ABBREVIATION

AC - Alternate Current

AL3O2 - Alumunium Oxide

BN - Boron Nitride

C - Graphene

C - Coulomb

CO2 - Carbon Dioxide

Cu - Cuprum

d - diameter

D - Flux density

DC - Direct current

E - Electric field

EPDM - Ethylene propylene diene monomer

F - Force

h - height

GUI - Graphical user interface

HDPE - High density polyethylene

HVAC - High voltage alternate current

HVDC - High voltage direct current

LDPE - Low density polyethylene

LLDPE - Linearly Low density polyethylene

N2 - Nitrogen

NSD - Nanometre-size silicon dioxide

NTD - Nanometre-size titanium dioxide

O2 - Oxygen

PE - Polyethylene

PVC - Polyvinyl Chloride

xiv

q,Q - Charges

r - radius

SF6 - Sulphur Hexafluoride

Si3N4 - Silicon Nitride

SiO2 - Silicon dioxide

TiO2 - Titanium dioxide

V/m - Volt per metre

XLPE - Cross linked polyethylene

εr - Permittivity of free space

εo - Relative permittivity constant

ρv - Free charge density

1

CHAPTER 1

INTRODUCTION

1.1 Project Overview

Transportation of electrical energy growth rapidly. One of major electrical energy

transportation is in direct current (DC) particularly at high voltage direct current

(HVDC). HVDC transmission quite favoured by energy supplier since HVDC loss is

comparatively low over high voltage alternate current (HVAC) at long distance [1]

and a sturdy cable is required for HVDC transmission in both subterranean and

submarine.

Today, cable manufacturers competitively producing good quality of cables

that able to withstand approximately at 500kV HVDC. Various types of cables

insulation are available in the market, but the one of the most popular cable insulation

is cross-linked polyethylene (XLPE). XLPE is remain as preferred insulation for cable

since it existence in 80’s era. A tremendous technology has been adapted and adopted

into XLPE to improve its strength.

In recent innovation, impurities consisting nanofillers compound are mixed to

anew XLPE insulation. Many researchers had conducted study, testing the capability

of XLPE with nanocomposites. Previous researches showed a manifold of

nanocomposites was tested such as silicon dioxide, titanium dioxide etc.

Thus, it is vital to study the impurities’ effects of nanocomposites towards

XLPE insulation. Especially, to seek explanation of effectiveness nanocomposites

toward the XLPE durability on DC breakdown. So, to further understand the concept

2

of nanocomposites in XLPE, this study is focused on unveiling the characteristic of

nanocomposites material against XLPE insulation.

Essentially, this study was divided into two parts, the first part was the selection

of nanocomposites which are silicon dioxide (SiO2), titanium dioxide (TiO2) and dry

air. Secondly, all the nanocomposites were being constructed and modelled in a

simulation application. The simulation software used in this paper is COMSOL

Multiphysics. The software provides a simple step by step with an interactively graphic

user interface. It was powerfully proven for solving and simulating many electrical

engineering problems. The outcome of COMSOL Multiphysics software application

is nearly accurate compared to real result.

From the simulated result, the related data obtained and compared. The

relationship of nanofillers in perspective of electric field and space charge in XLPE

will be determined. While, the effect of the nanofillers criteria in terms of sizing and

permittivity in XLPE also will be acquired.

1.2 Problem Statements

HVDC transmission exceptional properties leading to a huge investment in HVDC

polymeric cables mainly XLPE. However, under long term of usage, the dielectric

properties of XLPE insulation may change irreparable due to effects of degradation

and ageing process [2]. The changes also modify electric field criteria in XLPE

insulator and hindering the quality of power conductivity.

Additionally, XLPE cable progress in HVDC is slower than HVAC due to the

fact of few flaws in high scale power transmission. At an equal amount of power,

HVDC experiences more losses than HVAC owing to fact of space charge presence

around the conductor[3][4]. The space charge tabulation also influenced by the

landscape of electric field.

Despite that, a diversity of innovation had been researched on XLPE insulation

from time to time. One of the latest fast-growing modification is by adopting

nanofillers. Nanofillers caught many experts’ eyes in inventing new version of XLPE.

Common type of nanofillers that being extensively researched in polymeric insulation

are silicon dioxide, SiO2 and titanium dioxide, TiO2.

3

By some mean, the total impact of nanocomposites characteristics upon electric

field and space charge still uncertain. Therefore, it is become a necessity to analyse the

ability of different types of nanofillers and sizes in dictating XLPE quality.

1.3 Objectives

This project main purpose is to generate and simulate the condition of HVDC XLPE

insulator with impurities of nanofillers on electric field and space charge characteristic

effects. The simulation is run by COMSOL Multiphysics software. Thus, the

objectives of this project are:

i. To investigate the electric field and space charge’s characteristics on XLPE

insulator doped with different type of nanofillers.

ii. To analyse the electric field and space charge behaviour on XLPE insulator

with different size of nanofillers.

iii. To determine the best nanofiller among dry air, silicon dioxide and titanium

dioxide to be doped into XLPE insulator.

1.4 Project Scope

As state earlier, this project is to investigate as well as examine the properties of

nanocomposites in respecting to XLPE insulation. Thereby, to attain the project

objectives, several aspects had been identified as its own limitation and was pointed

out as this project scopes. The highlighted research scopes are stated as follows:

i. Simulation software

The modelling and evaluation of electric field and space charge in cable is

designed using COMSOL Multiphysics application software with certain

parameters value is preassigned.

ii. Cable

The designated conductor is copper, Cu and the insulator is cross-linked

polyethylene, XLPE.

4

iii. Nanofillers

The nanofillers selected to be embedded in XLPE insulator is limited to dry

air, silicon dioxide, SiO2 and titanium dioxide, TiO2.

iv. Variables analysis

Electric field and space charge characteristics will be determined by varying

the types and sizes of nanofillers.

1.6 Thesis Organisation

The present report encompasses of five chapters. The first chapter provide a brief

introduction to the background of research that covers problem statements, the

objectives, scope of the research and the significance of the research. Then, Chapter

Two highlights the details of literature review enclosing of polyethylene (PE) mainly

crosslinked polyethylene (XLPE), nanofillers attributed from silicon dioxide (SiO2),

titanium oxide (TiO2) and dry air. Also, a systematically explanation on electric field

and space charge alongside with the selected simulation software.

Chapter Three outlines the method used in simulation software to investigate

characteristics in XPLE doped with the chosen nanofillers from the scratches to the

end. While, Chapter Four presents the simulation’s results and with graphically related

analysis according to the objectives stated. Lastly, Chapter Five outlines the

conclusion and recommendation for future research.

5

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

A significant evolution in power distribution had lead a growing trade on energy

transmission at long distance. Since high voltage direct current (HVDC) offers greater

advantages over high voltage alternate current (HVAC)[1][5]. Many academic

research as well as cable manufacturers shows a huge interest in the HVDC energy

transmission. One of its primary challenges in HVDC transportation is cable insulator.

The major insulation material for cables either subterranean or submarine is

polymeric insulator. After decades, cross-link polyethylene (XLPE) insulator remains

prominent among all polymeric insulators. XLPE notable with its superior properties,

but it’s still unknown to withstand HVDC loss in long period of time. Trendily on

present day, many manufactures enhance XLPE substance by blending nanofillers

compound. Most ordinary nanofillers that being practice are SiO2 and TiO2.

Even so, the effects of nanofiller still become a conversations topic among

experts. Hence, this project tries to unravel two traits of nanofillers characteristics in

XLPE such different sizes and types. A simulation had been done by using COMSOL

Multiphysics software, to explore the effects of nanofillers sizes and types toward

XLPE electric field and space charge.

6

2.2 Cross-linked Polyethylene, XLPE

Cross-linked polyethylene or in well-known abbreviation XLPE is a form of

polyethylene (PE) polymer. Polyethylene also known as polyolefin are high molecular

weight hydrocarbons, that include low density polyethylene (LDPE), high density

polyethylene (HDPE) and cross-linked polyethylene (XLPE). As tabulated in Table

2.1, common PE molecular structure are relatively straight polymer chains, and

unbinding chemically. Typical PE’s materials can become brittle from oxidation and

are easily damaged by exposure to high temperature.

Table 2.1: Comparison of Polyethylene and Cross-linked Polyethylene (XLPE)

properties

Properties Polyethylene XLPE

Chemical

[6]

Molecule

structure

Molecule

bonding

Thermal Melting point

(º C) 110 [7] 100 [8]

Mechanical Breaking

Elongation (%) 515 [7] 600 [8]

On contrary, XLPE molecules are tied up in a three-dimensional network and

the bonding formation can sturdily withstand even at high temperature. Originally,

XLPE is made of the same polyethylene but with some additional organic crosslinking

byproduct under high pressure and heat [9]. As a result, crosslinking chains are bonded

within polyethylene layers chemically. So, the properties of polyethylene are change

from thermoplastic into an elastic material.

7

As an insulator, XLPE only has a lower dielectric loss compared to paper and

polyvinyl chloride (PVC). Hence, XLPE cables serve a lower of mutual capacitance

as well as reducing the charging and earth-leaking currents.

2.2.2 Previous Related Research of XLPE

Due to chemical structure of XLPE is firmer than other polyethylene based polymer,

many researchers favouring XLPE in their studies. With the demanding of HVDC

transmission, the durability, strength and lifespan of XLPE is being researched in

diverse conditions and aspects. From the smallest flaw in the beginning manufacturing

to the sturdiness at extreme ageing environment condition.

In 2012 Takayuki et al. [10] reported an improvement of space charges

behaviour in nanoscale carbon doped in XLPE. Again, the same characteristic being

studied in 2014 and 2015 but with different fillers[11][12] being blended which was

nanosilica. Even in the same year, due to high usage, the recycle ability of XLPE also

being evaluated [8].

2016 recorded an increase of analysis being done on XLPE insulators. The

dielectric properties of XLPE were being modelled with different type of cable cores

with different level of AC voltage[13]. While electric field properties with and without

nanocomposites bonding were analysed with different physical condition [2][14][15].

Many studies were proposed by researchers to seek the correlation of space charge

distribution in XLPE and nature environmental condition such as wetness,

temperatures and aging[16][17].

2.3 Nanofillers

Worldwide shows its interest in nanotechnology already reaching two decades. This

interest accompanied by the presence of nanofillers and nanocomposites, both in

scientific and commercial. The nanosized particles demonstrate an improvement in

polymer composites properties which attract plenty of researchers’ attention over the

years. Yet, the terminology of nanoparticles seems crucial since there are many

misconceptions and misuses in definition as well as understanding. According to R.

Rothon [18], various organization had introduced a standard for nanoparticles term

8

over decades. But even different in detail, a consensus is achieved for at least one

nanoparticles dimension in the range 1–100 nm, and others may be greater than

100nm.

Apparently, the definition of nanoparticles is restricted to those with three

nanometres dimensions. Hence, in today context [19], nanofillers is divided into three

categories, which are nanoparticles, nanofibers and nanoplates. Despite all the

publicity, nanoparticles had already in the exist in the present market. While, now the

freshness is lied on nanofibers and nanoplates which arrive later. Even so, nanoplates

receive more public attention due to relatively lower cost compared to nanofibers.

Individual properties of nanocomposite differ from its original bulk size matter

properties whether in physical, chemical or in biological [20][21]. Indirectly, it attracts

people attention toward opportunity for advancement in developing new standard of

materials. Without falling behind, electrical engineering field also adopting

nanocomposites in enhancing existing substances, includes insulating material. Up

until today, many types of nanofillers had been brought up for study. Among

sensational nanofillers are silicon dioxide, SiO2, titanium dioxide, TiO2, graphene, C,

aluminium dioxide, Al3O2, silicon nitride, Si3N4, boron nitride, BN, etc.

2.3.1 Silicon Dioxide

An acknowledgeable name of silicon dioxide is silica, the same materials for glass and

quartz. Silica is an inorganic compound made of most plentiful elements in earth which

are silicon and oxygen. Since antiquity, silica is well known for hardness and naturally

found both crystalline and amorphous states. An oxidized silicon atom produces the

silica compound with chemical formula is SiO2. A combination of one silicon atom

associated with two oxygen atoms.

Due to silica minerals extraction contaminated with metal, a synthetic silica

compound are created artificially at nanoscale size[20]-[22]. Nanoscale silicon dioxide

(NSD) had an astonishing achievement in research and industrial applications history,

including polymeric discipline. An illustrious example of NSD is as fillers to

cotemporary composite polymers, such as cable insulator. This filler’s application had

led to new advancement since silica nanofiller preserve the homogenous dispersion

9

feature[20]. The homogenous feature is a pivotal factor in determining the overall

performance of silica nanofillers.

2.3.1.1 Previous Related Research of Silicon Dioxide

The exceptional nanocomposite silica asset has captivated many researcher eyes to

study in various field. Over a decade, nano silicon dioxide (NSD) penetrated HVDC

insulation study and introduced to new level of insulation materials. As in 2011,

researchers [23] had started an experiment by fusing NSD with epoxy to investigate

thermal and dielectric characteristics of new filled epoxy resin, polyepoxides in HVDC

insulation. A slight drop was recorded to the breakdown strength compare to typical

epoxy.

While, at the same year, another research was conducted to examine the

distribution of space charge filled with NSD in LDPE [24]. Nanocomposites filled

LDPE influenced the resistivity increment towards temperature. A report of NSD

doped in silicon rubber was documented to determine the physical and chemical

properties. NSD gaining more popularity on insulating material, when N. A. M Jamail

et al. tested a linearly low-density polyethylene blending with natural rubber filled

(LLDPE-NR) with NSD in two consecutive years. One on effects of polarization and

depolarization current in 2012 and again a year later, on electrical tracking

performances[25][26]. Both indicated a better performance compared to pure LLDPE

insulator.

Then, an enhancement of mechanical and electrical properties was reported

for NSD added Polyvinylchloride (PVC) insulator compare to standard PVC

insulator[27]. Within 2014, two researches was carried out in different country to

understand the space charge distribution silica nanocomposite XLPE[11][28]. Besides

that, C. P. Sugumaran [29] had setup a study on testing the trait of PVC filled with

NSD on dielectric properties.

Recently in 2016, nanoparticles of silicon dioxide had indicated to be a good

nanofiller for liquid based insulator, transformer oil as reported by M. Rafiq [30]. Soon

after, nanosilica fumes is added experimentally to silicone rubber insulation for

dielectric properties purposed[31]. Lately, a simulation based study is proposed by

Aiswarya S. Nair et al. [32]to check the resistance of NSD on XLPE water treeing.

10

Before long, a correlation is investigated between electric field and breakdown

strength in XLPE filled with silica nanocomposites, the characteristic is modelled

using a simulation software[33].

Nowadays, previous studies showed that NSD had been noticed as one of

phenomenal compound to be added into insulation material. As illustrated in Figure 1,

NSD caught experts’ attention to deepen the knowledge on how far the traits and

properties of NSD as filler in insulator up until today.

Figure 2.1: Timeline of research on insulation materials with nanosilica doping.

2.3.2 Titanium Dioxide

Now, titanium dioxide has been available in wide range of products. It can be found

both inedible appearance in polymers, textiles, colourant even health and edible

products such as foods and drugs. It is a non-soluble inorganic substance that

physically in white that can withstand thermally [34]. Titanium dioxide or its different

name Titania had been discovered in various forms and sizes with chemical formula,

TiO2. The existence of titanium dioxide as additive had led to a diversity of usage [35].

Naturally, the arrangement of titanium and oxygen molecules within TiO2

differ their crystalline structures, whether in form of anatase or rutile. At nanomaterial,

TiO2 has different physical properties compared to its natural pigment state. Due to

2011

•Epoxy [22]

•LDPE [23]

2012

•LLDPE-NR[24]

2013

•LLDPE-NR[25]

•PVC [26]

2014

•XLPE [10]

2015

•PVC [27]

2016

•XLPE [28]

•Oil [29]

2017

•XLPE [30]

11

high surface to volume ratio, majority of nanoscale titanium dioxide (NTD) is

manufactured to improve the polymer properties in textiles, wood preservative, optic

and recently research area, insulation.

Titanium dioxide is added as an additive to improve the quality of the

insulation material. Lately, NTD has been caught eyes of many researchers either in

chemically structure, mechanically strength and electrical properties.

2.3.2.1 Previous Related Research of Titanium Dioxide

The main advantage of titanium dioxide over common nanocomposites is the value of

the permittivity constant. The relative permittivity, εr reaches to a level of 100, which

attracted many experts to discover the extraordinary properties of titanium dioxide

alias titania.

J. Zha and Z. Dang [36] had investigated the effect of breakdown strength and

space charge in polyimide with titanium oxide thin film. The result was showed that

the breakdown strength directly proportional to the concentration of titanium dioxide

fillers. A year after, researchers experimenting LDPE insulator by incorporating small

weightage of titanium dioxide. The experiment had demonstrated that the modified

LDPE recorded an overall increment of permittivity compared to pure LDPE [37].

Later in 2011, a local group of researchers[38] had discovered that the LLDPE-NR

tensile strength could be increased by the addition of titanium oxide nanofillers.

In 2013, an experiment was conducted to test electrical tracking in LLDPE-

NR, and titanium oxide filled LLDPE-NR had the least leakage current[26].

Meanwhile, few experts had tested the dielectric characteristics of titanium oxide

doped in LDPE and epoxy resins. A group of researchers [39][40] had investigated the

effect of a surface modification method for nanosized titania to be doped into LDPE

including the structure and the dielectric properties.

Then a simulation base study was conducted to examine the effect of water tree

at nanocomposites filled XLPE [32] The result shown common XLPE experienced a

higher electric stress from water treeing differ from XLPE mixed with titanium

dioxide. In the same year, an experimental test was conduct by few researchers, it was

found out that the XLPE with titanium dioxide as nanofillers recorded a higher

resistivity compared to standard XLPE [41].

12

Historically, titanium dioxide displayed an impressive performance when

added as additive to insulation materials, particularly in enhancing electrical

properties. This was due to the fact that the presence of titanium dioxide could

positively increase the overall properties of insulators. Therefore, indirectly from time

to time, NTD always picked as a selection by academia and manufacturers as one of

their nanocomposites in insulator.

2.3.3 Air

Natural air is consisted of various substances but most of it composition is gases.

nitrogen, N2 is highest gas molecules in atmosphere air with 78%, followed with

oxygen, O2 with at 21% and carbon dioxide, CO2 with 0.03%. Water vapour existence

in air is varied according to the environment heat, humidity and moisture. The rest of

air content is contaminated with aerosols or microscopic solid particles. However, the

minute solid particles can be classified as approximately zero since their existence is

very little. So fundamentally 99% of air is make up from nitrogen, N2 and oxygen, O2

molecules.

Nevertheless, history recorded that dry air is listed as one of the electronegative

gases in material science documents. Experts categorised air as one of their

electronegative gases along famously known sulphur hexafluoride, SF6 in chemical

physics world [42][43]. The interesting fact on electronegative gases are based on their

chemical bonding structures. The ability of these gases’ atoms that can attract and

absorb free electron to themselves. Their electron attachment process can be visualised

as:

Atom + e- + k → negative atomic ion (2. 1)

Therefore, due to the fact of electronegativity nature, there was some of these

gases had been selected for decades for insulation purposes. This insulation includes

electrical insulation material for high voltage conductivity either at electrical

equipments or cables.

Differently to SF6 which commonly equipped at indoor, air at atmospheric

pressure mostly applied as insulation gases for outdoor equipmment like at overhead

13

power line and open air substation [44]. A major factor is air’s capability to restore its

insulating properties after disconnecting from voltage.

2.4 Electric Field

Electric field is denoted as a vector force created in invisible line on per unit of

charge. The force generated due to attraction of opposite polarity and repulsion of

similar polarity of electric charges. As depicted in Figure 2.2, the line of electric field

for positive charge is perpendicularly heading onto outward direction of the charge

and for negative charge is heading into inward direction.

++ --

Figure 2.2: Electric field line of positive and negative charges

The electric field, E on motionless charge is proportionally to the force, F onto

it. Electric field is a charge can be simplified as:

�⃗� =𝐹

𝑞 (2. 2)

where E is electric field, F is force onto the charge and q is magnitude of the charge in

Coulomb, NC-1 also in international system of units (SI unit) is Vm-1.

Figure 2.2 showed two charges in a free space whereby, the force, Fq1 onto

charge q1 due to interaction by both charges, it can be demonstrated by Coulomb’s

Law. Magnitude of Fq1 cause by the two charges interacting to each other in free

space, denoted as q1 and q2 is expressed mathematically as:

14

𝐹 𝑞1 =𝑞1𝑞2

4𝜋𝜀0𝑑2 (2. 3)

where,

𝐹 𝑞1 = a vector force acting toward 𝑞1

𝑑 = 𝑑istance between 𝑞1 and 𝑞2

𝜀0 = permittivity of free space,8.854×10-12

Fm-1

Therefore, by substituting eq. 2.3 of Coulomb’s Law into eq. 2.2, the

magnitude of electric field for a single charge in a free space is deducted as:

�⃗� =𝑞

4𝜋𝜀0𝑑2 (2. 4)

2.4.1 The Importance of Electric Field

Now, the remaining question that need be answered is the indication of electric

field in insulation. Basically, insulation material is made of a material that obstructing

any electrical conductivity within in normal condition, and the material is called as

insulator. Regardless of any insulator, there are still having a maximum capacity of

voltage for insular to be endured, including XLPE. If the voltage applied exceeds

higher than the maximum voltage, the insulator losses it voltage blocking potential and

having a breakdown. Thus, allow electric current to flow through.

The maximum voltage can be accepted by insulator in ideal condition is widely

known as dielectric strength. Dielectric strength is depended onto two characteristics,

which are the relative permittivity and the thickness of the material itself, which in SI

unit is designated as Vm-1. Indirectly, the dielectric strength of an insulator having a

similar nature to the electric field. So, theoretically to decide the maximum tolerance

of a voltage in an insulator is by calculating the electric field.

15

2.4.2 Previous Related Research of Electric Field

In 2013, A. Tzimas et al. [45] had investigated the electric field distribution on

ethylene-propylene rubber (EPDM) with the presence of ageing effect. From the result,

the ageing criteria could had boosted up 50% of electric field amount.

While, L. Andrei et al. [46]had issued on electric field analysis with water tree

defected of an XLPE insulator. From the simulation result, it was showed that electric

field was increase at the defected area. Again, with the same water tree defected

characteristic, W. Tao et al. [15] had examined the electric field with different XLPE

insulator conditions both wet and dry.

At the same time, S. Wang et al. [47] had experimented the effect of

temperature of XLPE insulator with different type of electric potential sources, which

were AC and DC. However, from the outcome, it was showed that the electric field

strength become stronger as the temperature rose.

K. Lau et al. [33] had investigated the impact of nanosilica material in XLPE.

The electric field distribution in XLPE was different between AC and DC source, but

the presence of the nanosilica could increase the electrical breakdown strength of the

insulator.

2.5 Space Charge

Conceptually space charge is interpreted as a region of free charges built in short

distance within two types of different materials when an external field is applied. The

free charges can either be assemble from electrons, holes, or charge particle ions

which trapped or transported within dielectric material[48]. They region can be

depleted to achieve equilibrium or piled up thicker depending to the direction of

injected voltage supply. Figure 2.3 depicts the space charge continuum in two-

dimensional plane between two materials. They are treated in form of cloud rather than

distinctively pointed charge.

16

Figure 2.3: Space charge region between a conductor and an insulator

In power transmission context, normally the space charges are piled up along

on conductor’s surface since the supply is at the conductor side and ground at the outer

shield of insulator. In case of HVAC, the polarity of electrical conduction uniquely

changing from positive to negative and vice versa continuously. Hence, this distinctive

situation refrains the space charge region to be built along the conductor and

approximately equal to zero. So the space charge is assumed as nil and can be

neglected [3]. But unlike HVAC, HVDC polarity is different, stay unchanged. Thus,

the space charge continuum is accumulated radially around the conductor tube [49].

Due the intrinsic behaviour of polymeric insulation material, the trapped

electrical charges prone to accumulate and initiate the presence of space charge within

the material. The presence of space charge is directly relied upon the rate of

accumulation and removal. The differences between rate of accumulation and removal

led to the formation of space charge [50]. At long duration of exposure, this formation

engenders to high electrical stress zone. The space charge formation is according to its

charge’s location and condition. It can be classified into three types of formation [51].

Table 2.2 shows the type of space charge formation’s pattern within insulation

material. The pattern is classed correspond to their charges’ polarity at the vicinity of

electrode. The well-known terminology adopted for space charge pattern are

homocharges and heterocharges. Homocharges is referred to the accumulation charges

or ions with similar polarity to the adjacent electrode. While, heterocharges completely

in the opposite formation of homocharges where positive charges drifted toward

17

negative electrode and vice versa. The formation patterns of space charge are key

factor to track down the charges origin and its stress level status [52].

Homocharges is extricated charges trapped in insulation material from

neighbouring electrode primarily due to low of mobility. In the meantime,

heterocharges are produced from ionize charges of insulation material due to applied

voltage. Both pattern formation resulting a different impact for insulation material, but

according to [53], in LDPE, homocharges usually occurs at low temperature and

heterocharges normally above 50ºC.

Despite that the presence of heterocharges affects insulation material with

more negative impacts compared to homocharges. Heterocharges undermines the

insulator’s strength by elevating the non-uniform electric field to premature

failure[54].

Table 2.2: Type of space charge formation patterm

Polarities Formation Charge

Distribution Description

Voltage

Ground

q

r

• Both positive and negative charges

align at inside insulation

• A step function of charges occurs near

electrode and near to equilibrium

Voltage

Ground

q

r

• Homocharges

• Appear same polarity near the electrode

• Low mobility of charges

Voltage

Ground

r

• Heterocharges

• Migration charges to the opposite

polarity of electrode

• Imbalance mobility of charges

18

According to differential form of Gauss’ Law, free charge density, ρv in a

closed surface area can be expressed as divergence of flux density,�⃗⃗� :

𝜌𝑣 = ∇. �⃗⃗� (2. 5)

where ρv is defined as the total density of free charge accumulated over a in an

enclosed volume. While, the relationship of electric field, �⃗� to flux density, �⃗⃗� can be

expressed as:

�⃗⃗� = 𝜀�⃗�

= 𝜀0𝜀𝑟�⃗� (2. 6)

where;

�⃗� = a vector of electric field toward the radius

�⃗⃗� = a vector of flux density toward the radius

𝜀0 = permittivity of free space, 8.854×10-12 Fm-1

𝜀𝑟 = relative permittivity of a material

By substituting eq. 2.6 into eq. 2.5, the total space charge density of a material can be

described as:

𝜌𝑣 = ∇. 𝜀0𝜀𝑟�⃗�

= 𝜀0𝜀𝑟 . (∇. �⃗� ) (2. 7)

Generally, the total space charge density, ρv in a solid cylindrical volume can be

demonstrated as the total space charge, Q over a volume, V

𝑄 = 𝜌𝑣𝑉

= 𝜌𝑣𝜋𝑟2ℎ (2. 8)

By substituting eq. 2.7 into eq. 2.8, the total space charge of a insulation material is

described as:

𝑄 = 𝜀0𝜀𝑟 . (∇. �⃗� )(𝜋𝑟2ℎ) (2. 9)

19

Hence, from the equation, the quantity of space charges could disrupt the quality of

electric field in the insulation material.

2.5.1 The Importance of Space Charge

Space charge is well accepted by many researches in associating to accelerate

the insulation breakdown process [55]. Initially, in constantly long period of time, the

presence of space charge will escalate the electric field distribution within the material.

This situation contributes to the enhancement and development of electrical treeing.

Over time, the electrical insulation strength is weakened and lead to internally

insulation breakdown. It was evidently proofed by [56], the breakdown occurred in

one of developed electrical treeing in an experimental XLPE sample. In the meantime,

total of accumulation and concentration played a crucial part for the possibility of

breakdown. The denser the space charge region, the higher the probability of insulation

breakdown occurrence [57][58].

The effects of space charge are not limited to its density but the charge’s

polarity condition as well. The discussion on polarity condition is more focussed

towards on its pattern and dominance. The pattern is already being notified in previous

subsection which are homocharges and heterocharges. While, the description about

dominance explains the imbalance of space charge presence in between negative and

positive charge. An experimented evidence was found that in an electrically aged

sample, a downsizing of positive ions was spotted in both electrode with negatively

charge redistributed in bulk in XLPE [59].

However, the structure of the insulation material can’t be overlooked. It plays

an important role in providing the quality and quantity of space charge formation and

accumulation. Even the base material is exactly same, the chemically manufacturing

process that contribute to the rough structure of the polymer effecting the dielectric

properties of the insulation material[9].

20

2.5.2 Previous Related Research of Space Charge

Many previous research had been conducted to examine the content of space

charge whether giving an impact or vice versa towards insulating material. Lately

researchers across the globe also engage in investigating the effect of space charge

within insulator doped with nanofillers. A study in 2011 was carried out by K. Wu et.

al [24] to inspect the behaviour of space charge in LDPE with epoxy resin added as

nanocomposites. As a result, the presence of nanocomposites could restrain the

thickening of a space charge region at different temperature.

T. Arakane et al. [10] had conducted an experiment to study the effect of

graphene nanofillers within XLPE insulator. With the increase of the nanofillers, the

space charge accumulation could be suppressed. A group of researchers had

investigated the differences between a nanocomposite XLPE with an ordinary XLPE.

Nanocomposite XLPE evidently showed lower accumulation of space charge

compared to common XLPE [11]. Even little modification on insulation properties’

structure make a different impact on space charge behaviour pattern [12].

On contrary, as stated by Y. Zhou et al. [8], the occupancy of polyolefin

elastomer in HVDC insulator cable could help the space charge accumulation which

could reduce the cable’s overall performance. From an experiment carried out by M.

Hao et al. [14], space charge behaviour was reacted relatively to the thermal and

electric field transition. The space charge heap positively to the thermal increment.

2.6 COMSOL Multiphysics Simulation Software

One of available finite element method (FEM) software commercially in market today

is COMSOL Multiphysics. The term of FEM also referred to as finite element analysis,

a method to solve engineering and mathematical physic problems numerically.

COMSOL Multiphysics provides an efficient analysis involving electromagnetic,

thermal, and stress design simulation with coupled multi-field analysis.

By using the current solver technology, it comprises a family of analysis

modules with an interactive interface and user friendly. Even though in compact size

but powerful for solving, modelling and designing many applications. The software

consisting a specific module for every analysis. It is categorized into eight main

21

modules attributed from AC/DC, acoustics, chemical species transport,

electrochemistry, fluid flow, heat transfer, optics, plasma, radio frequency,

semiconductor, structural mechanics and mathematics analysis.

Generally, COMSOL Multiphysics is a software that particularly design for

engineering structural design solving problems. For electric field and space charge

problems, typically AC/DC modules are chosen. The outcomes of the design and

analysis are approximately precise compared to practical. In this study, a COMSOL

Multiphysics 5.0 is used, to simulate finely the model created.

2.6.1 Previous Related Research using COMSOL Multiphysics

COMSOL Multiphysics modelling software had been available almost two decades.

A lot of researchers around the world used this software to model and simulate

artificially to get the outcome of their research’s problems. It been proven over the

years, that this software could help and analyse with ideal configuration.

In 2011, W. Choo et al.[60] investigated the electric field distribution in XLPE

cable with different temperature gradient using COMSOL Multiphysics. It showed that

electric field is proportional to temperature differences. Two years later, again an

electric field distribution with 8 years ageing condition was discussed by A. Tzimas et

al. [45] using COMSOL Multiphysics as a medium for simulation at ethylene-

propylene rubber (EPDM) insulator at 132kV of voltage source.

At the same year, a group of researchers was studied the dielectric properties

of a LDPE insulator with nanosilica fillers with COMSOL Multiphysics [61]. A year

later the similar group used the same software to examine the electric field of XLPE

with different kind of defects[62]. Then, once more the researchers [46], simulated the

electric field feature in XLPE cable with water trees effect. For three consecutive

years, the researchers entrusted the software to solve and analyse their studies’

outcome.

Year, 2015 showed a plentiful of researches using COMSOL Multiphysics,

including M. Meziani et al. [57]that simulated the characteristic of electric field with

water trees defects under influence of space charge magnitude. Then, H. Uehara et

al.[63] was considering using COMSOL Multiphysics to examine the space charge

distribution with different temperature.

22

A. Das et al. [64] had investigated the electric field of silicon rubber insulator

with contaminated outer surface. While, B. Huang et al. [65][66] had inspected space

charge behaviour on oil and paper insulation material. From previous recent studies,

indicated that COMSOL Multiphysics is effectively proven for simulation

electromagnetic studies on insulator.

Table 2.2, displayed the related researches over the years on using COMSOL

Multiphysics for solving and modelling electromagnetic problems. It indicated that

COMSOL Multiphysics result could fulfil the criteria for numerical findings for solid

insulators.

Table 2.3: Sequence of COMSOL Multiphysics usage for measurement.

Year Author’s

Reference

Tested Field Tested Insulator

Electric Field Space Charge

2011 [60] ✓ XLPE

2013 [45] ✓ Ethylene-propylene rubber (EPDM)

2013 [61] ✓ LDPE

2014 [62] ✓ XLPE

2015 [46] ✓ XLPE

2015 [57] ✓ XLPE

2015 [63] ✓ XLPE

2016 [64] ✓ Silicon rubber

2016 [65] ✓ Oil and paper

2016 [66] ✓ Oil

2.7 Summary

This chapter had explained in detail the introductory and previous researches that

involved in nanocomposites polymeric insulation materials. The nanomaterials

adopted were silicon dioxide, titanium dioxide and air. As in review, nanofillers had

undergone various experiments to identify their ability in insulator. Historically, their

presence had increased the polymeric strength in all aspects including electrical

properties. In electrical properties, electric field and space charge were among major

criteria to determine the durability of an insulation components. To analyse those

characteristics, COMSOL Multiphysics has been chosen to demonstrated its ability to

numerically solve in findings basic criteria polymeric insulators.

23

CHAPTER 3

METHODOLOGY

3.1 Introduction

In this study, few steps had been thought to achieve the objectives stated in previous

chapter. This section explains the method in detail chronically from investigation

stages, to preliminary result findings. Then, few parameters of high voltage direct

current (HVDC) cable had been taken into account, such as thickness, normal rating

voltage and sizes of nanofillers. By using COMSOL Multiphysics 5.0 version, the

characteristic and structure is designed and modelled accordingly.

3.2 Project analysis of HVDC Cables

This study started with theoretical aspect of HVDC cable specification, mainly cross-

linked polyethylene (XLPE) as stipulated in IEC 60502-2, International Standard

Second Edition [67]. Then the relevant facts and knowledge of electric field and space

charge effect on typical HVDC cables had been reviewed. This is followed by an

analysis of study in COMSOL Multiphysics 5.0 version.

As portrayed in Figure 3.1, the initial stage of this project was begun with the

discovery of descriptive data of an HVDC cable configuration. After few selection and

presumption, then the next stage was the evaluation process to ensure the analysis is

precise and accurate to the real model. This process was repeated until the available

data and facts was read and carefully selected.

24

Start

Project selection and

configuration

Variables selection

Evaluation and

verification

Configuration stage:

specification and

presumption

Design Stage:

Modelling and Meshing

Simulation Stage:

Solving and Analysing

Analysis Result

Ok?

End

Yes

Yes

No

No

Figure 3.1:Project methodology flow chart

Subsequently, a model of XLPE cable was begun to be constructed precisely

according to IEC standard. In the finalised specification, all the material properties

including, voltage level, thickness, size and material types were inserted into the

software. Then meshes were generated using tools available in the software for

configuration’s setup.

As a consequence, a model of XLPE cable was completely designed and being

simulated and analysed according to parameters that being set at first stage. All the

simulation data is categorised appropriately and discussed.

66

REFERENCES

[1] A. Kalair, N. Abas, and N. Khan, “Comparative study of HVAC and HVDC

transmission systems,” Renew. Sustain. Energy Rev., vol. 59, pp. 1653–1675,

2016.

[2] S. Tantipattarakul, A. Vaughan, and T. Andritsch, “On the Effects of Molecular

Composition, Morphology and Ageing on the Electrical Properties of

Polyethylene,” 2016 IEEE, 2016.

[3] C. Zhou and G. Chen, “Space charge and AC electric breakdown strength in

polyethylene,” Annu. Rep. - Conf. Electr. Insul. Dielectr. Phenomena, CEIDP,

vol. 2015–Decem, pp. 106–109, 2015.

[4] C. Zhou and G. Chen, “The influence of frequency of AC component on space

charge behaviours in polyethylene under combined AC and DC electric fields,”

2014 IEEE Conf. Electr. Insul. Dielectr. Phenomena, CEIDP 2014, pp. 852–

855, 2014.

[5] G. Chen, M. Hao, Z. Xu, A. Vaughan, Cao, Junzheng, and H. Wang, “Review

of High Voltage Direct Current Cables,” 10 Csee J. Power Energy Syst., vol. 1,

no. 2, pp. 9–21, 2015.

[6] “XLPE Insulated Power Cables,” Univers. Cable Berhad, pp. 1–68, 1990.

[7] P. International, “LDPE ( Low Density Polyethylene ).”

[8] Y. Zhou, J. He, J. Hu, X. Huang, and P. Jiang, “Evaluation of

polypropylene/polyolefin elastomer blends for potential recyclable HVDC

cable insulation applications,” IEEE Trans. Dielectr. Electr. Insul., vol. 22, no.

2, pp. 673–681, 2015.

[9] N. Hussin and G. Chen, “Analysis of Space Charge Formation in LDPE in the

Presence of Crosslinking Byproducts,” IEEE Trans. Dielecgtrics Electr. Insul.,

pp. 126–133, 2012.

67

[10] T. Arakane et al., “Space Charge Accumulation Properties in XLPE with

Carbon nano-filler,” Proc. 2012 IEEE Int. Conf. Cond. Monit. Diagnosis, C.

2012, no. September, pp. 328–331, 2012.

[11] J. H. Nam et al., “Space charge formations and electrical conductities

characteristics of nano composite XLPE,” Proc. Int. Symp. Electr. Insul. Mater.,

vol. 500, pp. 445–448, 2014.

[12] I. M. Zimmerling, I. A. Tsekmes, P. H. F. Morshuis, J. J. Smit, T. J. Person, and

T. Geussens, “Space charge analysis of modified and unmodified XLPE model-

cables under different electric fields and temperatures,” Annu. Rep. - Conf.

Electr. Insul. Dielectr. Phenomena, CEIDP, vol. 2015–Decem, pp. 134–137,

2015.

[13] I. C. Popa and A.-I. Dolan, “Numerical modeling of power cables,” 2016 19th

Int. Symp. Electr. Appar. Technol., no. 1, pp. 1–6, 2016.

[14] M. Hao, A. Fazal, G. Chen, A. S. Vaughan, J. Cao, and H. Wang, “The impacts

of the temperature and electric field on the electrical characteristics in semicon-

bonded XLPE insulation,” 2016 IEEE, pp. 6–9, 2016.

[15] W. Tao, S. Song, Y. Zhang, and W. Hao, “Tree Region on the Dry or Wet

Condition in XLPE,” 2016 IEEE, pp. 0–3, 2016.

[16] Y. Wang, J. Wu, S. Yi, and Y. Yin, “Research of Simultaneous Measurement

of Space Charge and Conduction Current in Cross-linked Polyethylene,” 2016

Int. Conf. Cond. Monit. Diagnosis, pp. 78–81, 2016.

[17] W. Xial, L. I. U. Quanyui, Z. Xiaoyangi, W. U. Kaii, Z. Chong, and L. I.

Wenpeng, “Study on Space Charge Behavior of XLPE after Long-term Aging

under Temperature Gradient and DC Stress,” 2016 Int. Conf. Cond. Monit.

Diagnosis, pp. 741–744, 2016.

[18] R. Rothon, “Nanofillers,” no. November, pp. 0–35, 2016.

[19] D. M. Marquis, É. Guillaume, and C. Chivas-joly, “Properties of Nano fillers in

Polymer,” Nanocomposites Polym. with Anal. Methods, p. 261, 2005.

[20] I. A. Rahman and V. Padavettan, “Synthesis of Silica nanoparticles by Sol-Gel:

Size-dependent properties, surface modification, and applications in silica-

polymer nanocompositesa review,” J. Nanomater., vol. 2012, 2012.

[21] H. Chang and S.-Q. Sun, “Silicon nanoparticles: Preparation, properties, and

applications,” Chinese Phys. B, vol. 23, no. 8, p. 88102, 2014.

68

[22] C. C. M. Carcouët, Chemistry and Morphology of Silica Nanoparticles.

Technische Universiteit Eindhoven, 2014.

[23] M. Reading, Z. Xu, A. S. Vaughan, and P. L. Lewin, “The thermal and electrical

properties of nano-silicon dioxide filled epoxy systems for use in high voltage

insulation,” 2011 Electr. Insul. Conf. EIC 2011, no. June, pp. 493–497, 2011.

[24] K. Wu et al., “Study of the Space Charge Behavior in Polyethylene Nano-

composites under Temperature gradient,” Int. Conf. Electr. Insul. Mater., no.

50907050, pp. 84–87, 2011.

[25] N. A. M. Jamail, M. A. M. Piah, and N. A. Muhamad, “Effects of SiO2

nanofillers on Polarization and Depolarization Current (PDC) of LLDPE-NR

nanocomposite insulating materials,” PECon 2012 - 2012 IEEE Int. Conf.

Power Energy, no. December, pp. 707–711, 2012.

[26] N. A. M. Jamail, M. A. M. Piah, F. L. Muhamedin, N. F. Kasri, N. A. Muhamad,

and Q. E. Kamarudin, “Electrical tracking characterization of LLDPE-Natural

Rubber blends filled with nanofillers,” Annu. Rep. - Conf. Electr. Insul.

Dielectr. Phenomena, CEIDP, pp. 695–698, 2013.

[27] C. Pugazhendhi Sugumaran, “Diagnosis on mechanical and electrical properties

of cable insulation PVC with nanofiller,” 2013 IEEE 1st Int. Conf. Cond.

Assess. Tech. Electr. Syst. IEEE CATCON 2013 - Proc., pp. 223–226, 2013.

[28] L. Zhang, Y. Zhou, X. Cui, Y. Zhang, and Q. Ye, “Space Charge Behavior of

XLPE/SiO2 Nanocomposites with Nanoparticle Surface Modification,” 2014

Electr. Insul. Conf., no. June, pp. 402–406, 2014.

[29] C. P. Sugumaran and I. Member, “Experimental Study on Dielectric and

Mechanical Properties of PVC Cable Insulation with SiO 2 / CaCO 3

Nanofillers,” 2015 Annu. Rep. Conf. Electr. Insul. Dielectr. Phenom., pp. 503–

506, 2015.

[30] M. Rafiq, C. Li, Y. Lv, K. Yi, and I. Arif, “Breakdown Characteristics of

Transformer Oil Based Silica Nanofluids,” 2016 IEEE, pp. 1–4, 2016.

[31] M. Paredes, C. J. Angammana, and S. H. Jayaram, “Experimental Study of

Dielectric Properties of Fumed Silica / Silicone Composites,” 2016 IEEE, pp.

683–686, 2016.

69

[32] A. S. Nair, R. Krithika, P. Monika, N. Purnimaa, and D. Kavitha, “Influence of

Nanofillers on Resistance to Water Tree in XLPE Nano Composite,” 2016 Int.

Conf. Circuit, Power Comput. Technol. [ICCPCT], pp. 1–7, 2016.

[33] K. Y. Lau, M. A. M. Piah, and K. Y. Ching, “Correlating the breakdown

strength with electric field analysis for polyethylene/silica nanocomposites,” J.

Electrostat., vol. 86, pp. 1–11, 2017.

[34] T. D. S. Council, “About Titanium Dioxide,” 2013.

[35] T. Theivasanthi and M. Alagar, “Titanium dioxide ( TiO 2 ) Nanoparticles -

XRD Analyses – An Insight,” 2012.

[36] J. Zha and Z. Dang, “Effect of Breakdown Strength and Space Charge

Distribution in Polyimide/Ti02 Nanohybrid Films Aged by Corona Treatment,”

9th Int. Conf. Prop. Appl. Dielectr. Mater., no. l, pp. 796–799, 2009.

[37] L. Shengtao, Y. Guilai, N. Fengyan, B. Suna, L. Jianying, and Z. Tuo,

“Investigation on the dielectric properties of nano- titanium dioxide - low

density polyethylene composites,” 2010 Int. Conf. Solid Dielectr., no.

50625721, pp. 5–8, 2010.

[38] M. Z. H. Bin Makmud, A. Sayuti, Y. Z. Arief, and M. U. Wahit, “Insulating

performance of LLDPE/natural rubber blends by studying partial discharge

characteristics and tensile properties,” Proc. 2011 Int. Conf. Electr. Eng.

Informatics, ICEEI 2011, no. July, pp. 11–14, 2011.

[39] B. Zazoum, M. Fréchette, and E. David, “LDPE/TiO2 Nanocomposites: Effect

of POSS on Structure and Dielectric Properties,” IEEE Trans. Dielectr. Electr.

Insul., vol. 23, no. 5, pp. 523–526, 2015.

[40] B. Zazoum, M. Fréchette, and E. David, “Effect of POSS as Compatibilizing

Agent on Structure and Dielectric Response of LDPE / TiO 2 Nanocomposites,”

2015 Annu. Rep. Conf. Electr. Insul. Dielectr. Phenom., pp. 523–526, 2015.

[41] Y. Wang, K. Xiao, C. Wang, L. Yang, F. Wang, and A. Sample, “Study on

Dielectric Properties of TiO2/XLPE Nanocomposites,” 2016 IEEE Int. Conf.

High Volt. Eng. Appl., pp. 1–4, 2016.

[42] M. S. Naidu and V. Kamaraju, High Voltage Engineering, Second Edi.

McGraw-Hill, 1996.

[43] E. Kuffel and W S Zaengl, High Voltage Engineering Fundamentals, Second

Edi. Butterworth-Heinemann ©, 2000.

70

[44] J. P. Holtzhausen and W. L. Vosloo, High Voltage Engineering Practice and

Theory. Dr JP Holtzhausen (Standard Copyright License), 2011.

[45] A. Tzimas, C. Zachariades, and S. M. Rowland, “Electric field analysis of

132kV EPDM insulator and correlation with ageing features,” 2013 IEEE

Electr. Insul. Conf., no. June, pp. 210–214, 2013.

[46] L. Andrei, I. Vlad, and F. Ciuprina, “Electric field distribution in power cable

insulation affected by water trees,” 2015 9th Int. Symp. Adv. Top. Electr. Eng.

ATEE 2015, pp. 426–429, 2015.

[47] Shihang Wang, Peixing Chen, and Jianying Li, “Difference of Dielectric

Properties Between AC and DC XLPE Cable Used Insulation Materials,” Int.

Conf. Cond. Monit. Diagnosis, pp. 1705–1711, 2016.

[48] Z. XU, “Space Charge Measurement and Analysis in Low Density Polyethylene

Film,” University of Southampton, 2009.

[49] A. R. A. Raja, B. Vissouvanadin, T. T. N. Vu, G. Teyssedre, and N. I. Sinisuka,

“Space Charge Measurement on XLPE Cable for HVDC Transmission using

PEA Method,” 4th Int. Conf. Electr. Eng. Informatics (ICEEI 2013), vol. 11,

no. Iceei, pp. 327–333, 2013.

[50] J. L. Davidson, T. J. Williams, and A. G. Bailey, “Electrostatic discharges

between charged insulators and grounded spheres,” J. Electrost. 56, vol. 56, pp.

29–42, 2002.

[51] N. A. Othman, M. A. M. Piah, and Z. Adzis, “Charge distribution measurement

of solid insulator materials : A review and new approach,” Renew. Sustain.

Energy Rev., vol. 70, no. November 2016, pp. 413–426, 2017.

[52] R. J. Fleming, M. Henriksen, and J. T. Holbarll, “The Influence of Electrodes

and Conditioning on Space Charge Accumulation in XLPE,” IEEE Trans.

Dielectr. Electr. Insul., vol. 7, no. 4, pp. 561–571, 2000.

[53] S. Hwang-bo, J. Kim, D. Yi, M. Han, and E. X. I. E. Method, “Characterization

of Space Charges and Conduction Current in LDPE Modified PEA Method,”

1995 IEEE 5th Int. Conf. Conduct. Break. Solid Dielectr., p. 169, 1995.

[54] R. S. Arya and N. Toshikatsu, “Understanding treeing phenomena and space

charge effect in gamma-irradiated XLPE cable insulation,” Electr Eng (2011),

Springer-Verlag, pp. 199–207, 2011.

71

[55] M. Fukuma, K. Fukunaga, and T. Maeno, “Space Charge Dynamics in LDPE

Films Immediately Before Breakdown,” IEEE Trans. Dielectr. Electr. Insul.,

vol. 8, no. 2, pp. 2001–2003, 2001.

[56] Y. Zhang, J. Lewiner, C. Alquie, and N. Hampton, “Evidence of Strong

Correlation Between Space-charge Buildup and Breakdown in Cable

Insulation,” IEEE Trans. Dielectr. Electr. Insul., vol. 3, no. 6, pp. 778–783,

1996.

[57] M. Meziani, A. Mekhaldi, M. Teguar, and L. De Recherche, “Effect of

Magnitude of Space Charges on the Electric Field Distribution in XLPE

Insulation in Presence of Water Trees,” Jicable 2015, pp. 2–6, 2015.

[58] D. Min, W. Wang, and S. Li, “Numerical Analysis of Space Charge

Accumulation and Conduction Properties in LDPE Nanodielectrics,” Trans.

IEEE Dielectr. Electr. Insul., vol. 22, no. 3, pp. 1483–1491, 2015.

[59] G. C. Montanari and D. K. Das-Gupta, “Polarization and Space Charge

Behavior of Unaged and Electrically Aged Crosslinked Pol ye thy lene,” IEEE

Trans. Dielectr. Electr. Insul., vol. 7, no. 4, 2000.

[60] W. Choo, G. Chen, and S. G. Swingler, “Electric field in polymeric cable due

to space charge accumulation under DC and temperature gradient,” IEEE Trans.

Dielectr. Electr. Insul., vol. 18, no. 2, pp. 596–606, 2011.

[61] F. Ciuprina, L. Andrei, F. M. G. Tomescu, I. Plesa, and T. Zaharescu,

“Electrostatic Model of LDPE-SiO2 Nanodielectrics,” 2013 IEEE Int. Conf.

Solid Dielectr., no. 3, pp. 876–879, 2013.

[62] L. Andrei, I. Vlad, and F. Ciuprina, “Electric Field Distribution in Power Cable

Insulation Affected by Various Defects,” 2014 Int. Symp. Fundam. Electr. Eng.,

pp. 1–5, 2014.

[63] H. Uehara, Z. Li, Y. Cao, Q. Chen, and G. C. Montanari, “The effect of thermal

gradient on space charge pattern in XLPE,” Annu. Rep. - Conf. Electr. Insul.

Dielectr. Phenomena, CEIDP, vol. 2015–Decem, pp. 138–141, 2015.

[64] A. Das, D. K. Ghosh, and R. Bose, “Electric Stress Analysis of a Contaminated

Polymeric Insulating Surface in Presence of Dry Bands,” 2016 Int. Conf. Intell.

Control Power Instrum., pp. 89–92, 2016.

72

[65] B. Huang, M. Hao, Z. Xu, G. Chen, C. Tang, and J. Hao, “Research on thickness

ratio and multilayers effect on the oil and paper space charge distribution,” C.

2016 - Int. Conf. Cond. Monit. Diagnosis, pp. 40–43, 2016.

[66] B. Huang, M. Hao, J. Hao, J. Fu, Q. Wang, and G. Chen, “Space charge

characteristics in oil and oil-impregnated pressboard and electric field distortion

after polarity reversal,” IEEE Trans. Dielectr. Electr. Insul., vol. 23, no. 2, pp.

881–891, 2016.

[67] “IEC 60502-2 International Standard for Cable, Second Edition 2005-03.”

International Electrotechnical Commission, 2005.

[68] M. Klampar, M. Spohner, P. Skarvada, D. Dallaeva, and J. Kobrtek, “Dielectric

Properties of Epoxy Resins With Oxide Nanofillers and Their Accelerated

Ageing,” 2013 Electr. Insul. Conf., no. June, pp. 286–290, 2013.

[69] H. J. Visser, “Physical Constants and Material,” in Antenna Theory and

Applications, First Edit., John Wiley & Son, Ltd., 2012, pp. 2–3.

[70] T. K. Gupta, “Dielectric Materials,” in Copper Interconnect Technology,

Springer Science Business Media, 2009, p. 71.

[71] A. Wypych et al., “Dielectric Properties and Characterisation of Titanium

Dioxide Obtained by Different Chemistry Methods,” J. Nanomater., vol. 2014,

2014.

[72] E. Terzic, “Capacitive Sensing Technology,” in A Neural NEtwork Approach

to Fluid Quantity Measurement In Dynamic Environment, Springer Verlag

London, 2012.

[73] J. C. Fothergill, J. K. Nelson, and M. Fu, “Dielectric properties of epoxy

nanocomposites containingTiO2, Al2O3 and ZnO fillers,” 17th Annu. Meet.

IEEE Lasers Electro-Optics Soc. 2004. LEOS 2004., no. type 1255, pp. 406–

409, 2004.

[74] S. S. Gevorgian, “Dielectric , Mechanical , and Electromechanical Properties of

Ferroelectrics and Piezoelectrics,” in Tuneable Film Bulk Acoustic Wave

Resonators, Engineering Material and Processes, Springer Verlag London,

2013.

[75] N. A. B. M. JAMAIL, “Polarization and Depolarization Current Of Linear Low

Density Polyethylene-Natural Rubber Nanocomposite Subjected to Electrical

Tracking and Moisture,” Universiti Teknologi Malaysia, 2015.

73

[76] R. J. Fleming, T. Pawlowski, A. Ammala, P. S. Casey, and K. A. Lawrence,

“Electrical Conductivity and Space Charge in LDPE containing TiO 2

Nanoparticles,” IEEE Trans. Dielectr. Electr. Insul., vol. 12, no. 4, pp. 745–

753, 2005.

[77] Y. Yamada, S. Yamanouchi, and S.Miyamoto, “The Relation Between Voids in

XLPE Insulation and Electrical Breakdown Strength of XLPE Insulated

Cables,” 1985 IEEE, no. 1, pp. 313–322, 1985.

[78] M. H. M. Sharif, N. A. M. Jamail, N. A. Othman, and M. S. Kamarudin,

“Analysis of Electric Field and Current Density on XLPE Insulator,” Int. J.

Electr. Comput. Eng., vol. 7, no. 6, pp. 3095–3104, 2017.

[79] J. Hjerrild, J. Holboll, M. Henriksen, and S. Boggs, “Effect of Semicon-

Dielectric Interface on Conductivity and Electric Field Distribution,” IEEE

Trans. Dielectr. Electr. Insul., pp. 596–603, 2002.

[80] A. Kumada and S. Okabe, “Charge Distribution Measurement on a Truncated

Cone Spacer under DC Voltage,” IEEE Trans. Dielectr. Electr. Insul., vol. 11,

no. 6, 2004.

[81] J. Lewiner, “Evolution of Experimental Technique for Study of The Electrical

Properties of Insulating Materials,” IEEE Trans. Electr. Insul., no. 3, 1986.

[82] B. Alijagic-Jonuz, P. H. F. Morshuis, and J. J. Smit, “Changing of Space Charge

Related Material Properties Due to Electrical Aging,” Proceeding 7th Int. Conf.

Prop. Appl. Dielectr. Mater., pp. 904–908, 2003.

[83] Z. Li, Y. Yin, X. Dong, X. Li, and D. Xiao, “The effect of filler content on slow

polarization behavior in composite of nano-SiOx or micro-SiO2 and low-

density polyethylene,” 2007 Int. Conf. Solid Dielectr., pp. 415–418, 2007.

[84] M. Mammeri, C. Laurent, and M. Nedjar, “Dynamics of Voltage Polarity

Reversal as the Controlling Factor in Space-charge Induced Breakdown of

Insulating Polymers,” IEEE Transacfions Dielecfrics Electr. Insul., vol. 4, no.

1, pp. 44–51, 1997.

[85] J. Zha and Z. Dang, “Effect of Breakdown Strength and Space Charge

Distribution in Polyimide/Ti02 Nanohybrid Films Aged by Corona Treatment,”

in Proceedings of the 9th International Conference on Properties and

Applications of Dielectric Materials, 2009, no. l, pp. 796–799.

74

[86] Z. Junwei, D. Zhimin, and G. Chen, “Preparation and charge transport of

polyimide insulating nanocomposite films,” in Electrical Insulating Materials

(ISEIM), Proceedings of 2011 International Conference on, 2011, pp. 20–22.

[87] T. Takada, “Acoustic and optical methods for measuring electric charge

distributions in dielectrics,” IEEE Trans. Dielectr. Electr. Insul., vol. 6, no. 5,

pp. 519–547, 1999.

[88] M. Florkowski, B. Florkowska, and P. Zydron, “Observations of echo

phenomena acquired from partial discharge measurements in voids,” in ICHVE

2016 - 2016 IEEE International Conference on High Voltage Engineering and

Application, 2016, pp. 2–5.

[89] L. Chen, Z. Zheng, M. Chen, and H. Yu, “The study of the discharge mechanism

and characteristics of micro-voids in the solid dielectric,” in ICHVE 2012 - 2012

International Conference on High Voltage Engineering and Application, 2012,

pp. 575–578.

[90] X. Wang, N. Yoshimura, D. Tu, Y. Tanaka, and T. Takada, “Distribution

characteristics and formation mechanism of space charge in PE materials,” in

Proceedings of 1998 International Symposium on Electrical Insulating

Materials. 1998 Asian International Conference on Dielectrics and Electrical

Insulation. 30th Symposium on Electrical Insulating Materials (IEEE Cat.

No.98TH8286), 1998, pp. 109–112.

[91] Y. Zhou, J. Hu, B. Dang, and J. He, “Effect of different nanoparticles on tuning

electrical properties of polypropylene nanocomposites,” IEEE Trans. Dielectr.

Electr. Insul., vol. 24, no. 3, pp. 1380–1389, 2017.