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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
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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
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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.
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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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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.
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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.
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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.
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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.
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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
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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
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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.
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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]
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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].
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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
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