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KING SAUD UNIVERSITYDEANSHIP OF SCIENTIFIC RESEARCH

Research Center – College of Engineering

Final Research Report No. EE-18/26/27

EFFECT OF THERMO-ELECTRICAL

STRESSES AND ULTRA-VIOLET

RADIATION ON POLYMERIC

INSULATORS

By

Dr. Y.Z. Khan, Prof. A.A. Al-Arainy,

Prof. N.H. Malik, andDr. M.I. Qureshi



Table of Contents

Page

List of Tables iii

List of Figures ivAcknowledgement vii

Abstract (Arabic) viiiAbstract (English) ix

Nomenclature x

CHAPTER 1: INTRODUCTION 1

1.1 Polymer Insulators: Advantages and Disadvantages 3

1.1.1 Advantages 3

1.1.2 Disadvantages 5

1.2 Types of Insulating Materials 5

CHAPTER 2: LITERATURE REVIEW AND DATA COLLECTION 8

2.1 Introduction 8

2.2 Basic Polymeric Insulators Components 9

2.2.1 Core 92.2.2 Weather Sheds 10

2.2.3 Housings 132.2.4 End Fittings 14

2.3 Insulator Types 142.4 Weathersheds of Polymeric Materials 17

2.5 Testing Methods of Composite Insulators 21

2.6 Test Results of Composite Insulators 222.7 Ranking of Materials for Outdoor Insulation 26

2.8 Effect of Voltage Polarity on Performance 28

2.9 Properties of Pollution on Polymeric Insulators 302.10 Artificial Contamination on Polymeric Insulators 32

2.11 Aging of Polymeric Insulators and Mechanisms of Failure 33



Page

CHAPTER 3: EXPERIMENTAL SETUP AND PROCEDURES 45

3.1 Significance of Accelerated Aging of Polymeric Insulators 45

3.2 Accelerated Aging Cycle 473.3 Design of Accelerated Aging Test Chamber 48

CHAPTER 4: RESULTS AND DISCUSSIONS 58

4.1 Lightning Impulse Withstand Tests 58

4.2 Dry and Wet Power-Frequency Withstand Tests 60

4.3 Scanning Electron Microscopy (SEM) of Samples 624.4 Hydrophobicity 64

4.5 X-Ray Photoelectron Spectroscopic (XPS) Analysis 65

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 72

5.1 Conclusions 72

5.2 Recommendation for Future Work 73

REFERENCES 74

ANNEX – I 88

ANNEX – II 90



List of Tables

Table No. Title Page

2.1 Polymer Insulator Data for Saudi Electricity

Company (SEC-EOA). 42

3.1 Details of insulators under test. 53

4.1 Concentration (%) of elements detected byXPS. 69



List of Figures

Fig. No. Title Page

1.1 Composite insulators used in the world [1]. 2

1.2 Classification of insulating materials. 6

2.1 Components of polymer insulator. 9

2.2 Surface resistance of bare and silicone-coated porcelain insulators under salt fog conditions

[3]. 12

2.3 Dead End / Suspension type polymeric

insulators (~15 kV). 14

2.4 Line post type polymeric insulators (~15 kV). 15

2.5 Photographs of the lines with suspension type

insulators. 16

2.6 Line post insulators. 16

2.7 Guy strain type polymeric insulators. 17

2.8 Dependence of the withstand voltage on

(equivalent salt deposit density) ESDD in SIRand porcelain insulators [3]. 24

2.9 Cumulative charge in EPDM and HTV-SIRrods during exposure to energized salt-fogshowing the differences between ac (60 Hz),

+dc and –dc. Conditions: conductivity of thesaline water forming the fog is 250 µS/cm;

electrical stress is 0 6 kV/cm [29] 29



List of Figures

Fig. No. Title Page

2.11 Electric field along an insulator as a function

of shed number showing the effect of threesimulated defects placed in a groove in EPDM

insulator. Lengths of defects, 16 to 32 cm[65]. 38

3.1 Accelerated aging cycle. 48

3.2a Schematic diagram. 49

3.2b Photograph of test chamber for accelerated

aging cycle. 49

3.3 Spectrum comparison of sunlight & UVradiation [76]. 51

3.4a Schematic diagram of 28 kVL-L polymeric

insulator. 52

3.4b Dead End/ Suspension polymeric

insulator(EPDM and TPE). 52

3.5a Photograph of transformer used. 53

3.5b Transformer connections used in testing. 54

3.6 Temperature variation on insulator surface(under no load) and UV-A radiation level inthe Central region of Kingdom (Riyadh). 55

3.7 Temperature rise and fall variation in

Chamber 56



List of Figures

Fig. No. Title Page

4.2 Schematic of tests under lightning impulse

voltage. 59

4.3 Comparison of flashover voltages underlightning impulses of both polarities. 60

4.4 AC setup for testing of one unit of suspensioninsulator. 61

4.5 Flashover voltage under 60-Hz AC voltage. 62

4.6 SEM micrographs for new and the aged

samples of SiR and TPE insulators. 64

4.7 XPS analysis of SiR. 67

4.8 XPS analysis of TPE. 68



ACKNOWLEDGEMENT

The authors would like to thankfully acknowledge the assistance and

financial support provided by the Research Center, College of Engineering,

through research project grant No. 18/426. Sincere thanks are extended to the

staff of High Voltage Laboratory, Electrical Engineering Department where

most of the experimental work was carried out.



لمل ص

وه ي تن تج ت ستخدم الب ولمرات عل ى نط اق واس ع ف ي آثي ر م ن التطبيق ات الكهربائي ة

تستخدم العوازل البولميرية بصورة متزاي دة ف ي خط وط.وتستخدم في المملكة العربية السعودية

ة آبي رة الخ صائص الكهربائي ة لتل ك الع وازل بالعوام لتت أثر ب ص.النق ل والتوزي ع الكهربائي ة

تلك الع وازل البولمبري ة الم ستخدمة ف ي خط وط الق وى.البيئة هذه الدراسة تهدف إلى تقويم أدا

رس ت أثير األش عة ف وق.الكهربائي ة تح ت الظ روف البيئ ة للمنطق ة الوس طي م ن المملك ة

د

أدا

ى

عل

رارة

الح

ة

درج

اع

وارتف

سجية

وازلالبنف

الع

ك

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وطب

مم

ص

دف

اله

ذا

ه

ق

ولتحقي

الظروف المناخية المحلية وذلك باس تخدام نظ ام المواص فات الدولي ةلمحاآ)تعتي(نظام تعمير )IEC 61109(ا هيلع تاليد عتلا ض عب لا خدإ ع م.ة يئابرهكلا صئاص خلا ت نروق د قو

.عميروالبصرية والمظهرية والكيمياية لتلك العوازل قبل وبعد الت

أدا م ن الب ولمر))TPEأظهرت اختب ارات الع زل أن الب ولمر المط اطي الم رن أف ضل

بSiR ( (حي ث بين ت النت ائج إنخف اض ج ودة الع زل يع د التعمي ر ل ) )SiRالمط اطي ال سليكوني

10%و

صاعقي

ال

الجهد

حالة

في

7%ة

حال

ي

ف

ذآر

ي

ر

التغي

ن

يك

م

ول

ردد

المت

د

الجه

ة

حال

ي

ف )TPE. ( بولزاو علا حط سأ ةنوش خ دا يدزا ةيرص بلا تارا بتخالا جئا تن تر هظأ ة لثامم ةف

تغيي ر ي ذآر عل ى أس طح الع وازل الم صنوعة م ن ) )SiRالمصنوعة من مع التعمير ول م يط را

)TPE. (لزاوع حطسأ ةنوشخ دايدزا)SiR (ي ف صقا نت ببس ي دق ةئيبلا لماوعلل ضرعتلا دعب

.جودة العزل لتلك العوازل



ABSTRACT

Polymers are widely used for a variety of electrical applications and are

being produced and used in the Kingdom of Saudi Arabia. Polymeric

insulators are finding increasing applications in overhead transmission and

distribution lines. The electrical properties of such polymers are strongly

influenced by environmentally induced degradation mechanisms. A survey

was carried out by the authors to determine the state of non-ceramic insulators

being used by the power utilities in the Kingdom. To check the suitability of

the polymeric insulators, an experimental investigation was also carried out.

This experimental investigation is aimed at assessing the performance of

polymeric insulators used in high voltage overhead transmission and

distribution networks in the environmental conditions of central Saudi Arabia.

The effects of ultraviolet radiation and heat on the polymeric insulators were

studied. To achieve this objective, an accelerated aging test chamber was

designed and implemented to simulate local atmospheric conditions based on

the modified IEC standard 61109. Electrical withstand and Scanning Electron

Microscopy (SEM) based optical, visual and X-Ray Photoelectron

Spectroscopy (XPS) based chemical analytical results of the laboratory aged

insulators were compared with the new ones.

Dielectric performance shows that Thermoplastic Elastomer (TPE)

insulators outperform SiR insulators, since the reduction under aging exceeds

10% under lightning impulse while it amounts to around 7% under power

frequency test voltage while TPE insulator exhibit just minor reduction.

Similarly, the optical results indicate that surface roughness of the aged



NOMENCLATURE

SEM Scanning Electron Microscopy

XPS Photoelectron Spectroscopy

TPE Thermoplastic Elastomer

SiR Silicon Rubber

UV Ultraviolet

PTFE Poly Tetra Floro EthylenePE Polyethylene

EPDM Ethylene Propylene Diane Monomer

EPR Ethylene Propylene Rubber

RTV Room Temperature Vulcanized

HTV High Temperature Vulcanized

EPM Ethylene Propylene MonomerIEC International Electrotechnical Commission

EVA Ethylene Vinyl Acetate

HDPE High-Density Polyethylene

PUR Polyurethene

ATH Alumina Trihydrate

ANSI American National Standards Institute

NEMA National Electric Manufacturers Association

ESDD Equivalent Salt Deposit Density

NSDD Non-Soluble Deposit Density

ESCA Electron Spectroscopy for Chemical Analysis

FTIR Fourier Transform Infrared

LMW Low Molecular Weight

GC Gas ChromatographyMS Mass Spectrometer

TGA Thermogravimetric Analysis

RIV Radio Influence Voltage

SEC Saudi Electric Company



1

CHAPTER 1

INTRODUCTION

Overhead line insulators are used to support the line conductors at

towers or poles and to separate them electrically from each other.

Traditionally, line insulators have been produced using high quality glazed

porcelain and pre-stressed or toughened glass. Extensive research and service

experience has shown that these materials are very reliable and cost effective

for a majority of outdoor applications. However, since early sixties, alternative

materials namely polymers have emerged and presently are being used

extensively for a variety of outdoor insulator applications. Polymeric

insulators are increasingly being used in both the distribution and transmission

voltage ranges and are steadily capturing a wider share of the market.

Initially, polymeric insulators (also called composite or non-ceramic

insulators) were considered as replacement for porcelain and glass for special

applications such as areas with high incidences of vandalism, urban locations



2

tracking and erosion of polymer sheds, chalking and crazing of sheds which

lead to increased contamination collection, arcing and flashover, bonding

failures and electrical breakdowns along the rod-shed interface, corona

splitting of sheds and water penetration which lead to electrical breakdown.

Today polymeric insulators are in use on lines operating up to 765 kV.

However, they are more popular on transmission levels from 69 kV through

345 kV. A recent worldwide survey showed that there are thousands of

polymeric insulators in service at all voltage levels.

Fig. (1.1) shows the results of a CIGRE survey done in 2000 to

investigate the global distribution of composite insulators at voltage levels

above 100 kV [1]. Middle East is one of the regions where composite

insulators are gaining ground.

10

100

1000

10000

100000

1000000

N o

o f I n s u l a

t o r s

SiR

Others

Total



3

1.1 POLYMER INSULATORS: ADVANTAGES AND

DISADVANTAGES

1.1.1 Advantages

The primary impetus for polymeric insulators increased acceptance by

the usually cautious electric power utilities as discussed before, is their

substantial advantage compared to inorganic insulators which have primarily

been porcelain and glass. One of their major advantages is their low surface

energy and thereby maintaining a good hydrophobic surface property in the

presence of wet conditions e.g. fog, dew and rain. Other advantages include:

(1) Light weight which results in a more economic design of the towers or

alternatively enabling to upgrade the voltage of existing systems

without changing the tower dimensions. An example of this was a case

in Germany where the voltage was increased from 245 to 420 kV and

in Canada where two 115 kV, 50 km long lines were up-rated to 230

kV using horizontal polymer insulators on the same towers. The light

weight of the composite insulator strings also permits an increase in the

clearance distance between the conductor to ground and an increase in



4

light weight of the composite insulators also obviates the need to use

heavy cranes for their handling and installation and this saves on cost,

(2) A higher mechanical strength to weight ratio which enables the

construction of longer spans of towers,

(3) Line post insulators are less prone to serious damage from vandalism

such as gunshots which cause the ceramic insulators to shatter and drop

the conductor to the ground,

(4) Much better performance than ceramic insulators in outdoor service in

the presence of heavy pollution as well as in short term tests,

(5) Comparable or better withstand voltage than porcelain and glass

insulators,

(6) Easy installation thus saving on labor cost, and

(7) The use of composite insulators reduces the maintenance costs such as

of insulator washing which is often required for ceramic and glass

insulators, in heavily contaminated environment.



5

1.1.2 Disadvantages

The main disadvantages of composite polymeric insulators are:

(1) They are subjected to chemical changes on the surface due to

weathering and from dry band arcing,

(2) Suffer from erosion and tracking which may lead ultimately to the

failure of the insulator,

(3) Life expectancy is difficult to evaluate, and

(4) Faulty insulators are difficult to detect.

1.2 TYPES OF INSULATING MATERIALS

In fact, there are hundred of insulation materials which are used

in the electrical power industry. All such materials can broadly be classified

into different categories: such as gases, liquids, solids, vacuum and

composites [2,3].



6

A summary of insulation materials used in electrical networks is shown

in Fig. (1.2).

Materials

Conductor Insulator Semiconductor

CompositeVacuumSolidsLiquidsGases

Organic Polymer Inorganic

Thermoplastic Thermosetting

Nylon Polyethylene Epoxy resinsCrosslinked

polyethylene

Polystyrene Polypropylene Phenolics

Urea

Formaldehyde

PolycarbonatePolyvinyl

chloride Melamine Elastomers



8

CHAPTER 2

LITERATURE REVIEW AND DATA COLLECTION

2.1 INTRODUCTION

Polymeric insulators are being accepted increasingly for use in outdoor

installations by the traditionally cautious electric power utilities worldwide.

They currently represent 60 to 70% of newly installed HV insulators in North

America [1]. The tremendous growth in the applications of non-ceramic

composite insulators is due to their advantages over the traditional ceramic

and glass insulators. These include light weight, higher mechanical strength to

weight ratio, resistance to vandalism, better performance in the presence of

heavy pollution, in wet conditions and comparable or better withstand voltage

than porcelain or glass insulators. However, because polymeric insulators are

relatively new, the expected lifetime and their long-term reliability are not

well known and therefore are of concern to users. Additionally they might



9

2.2 BASIC POLYMERIC INSULATORS COMPONENTS

The basic construction of a polymer insulator for overhead line

applications consists of a core, weather sheds, and metal end fittings as shown in

Fig. (2.1).

Fig. (2.1): Components of polymer insulator.

2.2.1 Core

The core of a non-ceramic insulator has the dual burden of being the

main insulating part and of being the main load-bearing member, be it in

suspension, cantilever, or compression modes. For suspension and line post

insulators, the core consists of axially aligned, glass fiber-reinforced resin

containing 70 to 75% by weight of glass fiber. The fiber diameter ranges from



10

The end seal is considered to be the most important element of the

design of a non-ceramic insulator. Field failures have occurred due to brittle

fracture of the fiberglass rod as a consequence of the breach of the end seal,

thereby allowing the rod to come into contact with atmospheric pollutants and

moisture. Tracking of the fiberglass rod leading to failure has also been

observed in non-ceramic insulators.

Non-ceramic insulator end seals have three basic types: glued, friction,

and bonded types. Glued type seals that are made using a sealant material have

not proven to be permanent, generally because of poor adhesion. Friction-type

seals in which the sleeved core fits into the hardware are quite effective, as

long as the dimensional tolerances are maintained, and do not cause any

problems, provided that no movement of the fitting occurs. End seals that are

made by molding the sleeved core material onto the end fitting are by far the

best because of the better physical bond obtained during molding.

2.2.2 Weather Sheds

Sheds made from various non-ceramic materials for electrical

applications are shaped and spaced over the rod in various ways to protect the

rod and to provide maximum electrical insulation between the attachment



11

However, only the elastomeric materials have shown success in outdoor

electrical insulation applications, with silicone elastomer meeting all of the

requirements for long-term performance in practically all environments.

The polymers have the ability to interact with pollutants and reduce the

conductance of the pollution layer. This is illustrated in Fig. (2.2) [3]. The

important characteristic of the polymeric insulator which controls the

conductance is due to hydrophobicity (or water repellency) of its surface. On a

hydrophobic surface, water drops bead up and do not wet the surface

completely. This reduces the leakage current and the probability of dry band

formation, which leads to a higher flashover voltage. It has been observed that

the hydrophobicity is maintained in silicone rubber materials even after many

years in service, and it is this attribute that is responsible for the superior

contamination performance of silicone rubber family of materials when

compared to other polymers. The recovery of hydrophobicity is mainly due to

(i) a diffusion process, in which the low molecular weight polymer chains

migrate to the surface thereby forming a thin layer of silicone fluid and (ii)

reorientation of surface hydrophillic groups away from the surface. These

processes are temperature dependent and higher temperature causes their more

rapid recovery.



12

Fig. (2.2): Surface resistance of bare and silicone-coated porcelain insulators

under salt fog conditions [3].

It has been reported that Ethylene Propylene Diane Monomer (EPDM)

and silicone elastomeric materials containing a minimum of 70% by weight of

hydrated alumina that are in use by most of manufacturers are favored for

weathersheds with silicone rubber showed the best performance over all other

types [3]. Failures of some first generation polymeric insulators with epoxy

resin weathersheds have been attributed to depolymerization by the hydrolysis.

Depolymerization refers to the destruction of the molecular structure of the

polymer material. Hydrolysis is the result of a chemical reaction, which takes

place between the ions of water and the free ends of polymer's chemical chain,



13

curing of the resin is uneven. Circumferential cracks between sheds sometimes

develop during storage of the insulator because of the locked-in stresses.

However, more often the cracks develop in service as the stresses are

aggravated by low temperature and line tension. The cracks extend down to

the core, thereby exposing the core to the moisture. Elastomers are the best

weathershed materials, as they do not contain locked-in mechanical stresses

from the curing process. Also, elastomers are preferred at low temperatures

where impact resistance is important.

Another problem that surfaced early in the experience of first

generation designs was the effect of outdoor weathering on weathersheds.

Weathering affects all polymer materials to some extent and being a natural

phenomenon includes the effects of heat, humidity, rain, wind, contaminants

in the atmosphere and ultraviolet rays of the sun. Under such conditions, the

weathersheds of polymer insulators may permanently change physically by

roughening and cracking and chemically by the loss of soluble components

and by the reactions of salts, acids and other impurities deposited on the

surface. Surface becomes hydrophilic and moisture can more easily penetrates

into the volume of the weather sheds.

2 2 3 H i



14

employ a sheath made of insulating material between the weathersheds and the

core. This sheath is part of the housing.

2.2.4 End Fittings

End fitting transmit the mechanical load to the core. They are usually

made of metal.

2.3 INSULATOR TYPES

Three types of insulators are in common use i.e. the suspension/dead-end

type, line post insulators and Guy strain type insulator, as shown in Figs. (2.3)

and (2.4). The only significant differences among these are in the design of the

attachment hardware and in the size of the core, which is much larger for post

insulators.

15



15

Fig. (2.4): Line post type polymeric insulators (~15 kV).

(a) Dead-End/Suspension Type Insulators

This type of insulator is used where line conductor weight subjects the

insulator core to tension forces. The dead-end / tension insulator horizontally

supports the line conductor whereas suspension insulator vertically supports the

line conductor as shown in Fig. (2.5). Both are subject to tensile and torsional

loads.

16



16

Fig. (2.5): Photographs of the lines with suspension type insulators.

(b) Line Post / Station Post Insulators

The line post/ station post insulators horizontally or vertically support

the line conductors as shown in Fig. (2.6). Such an insulator is subjected to

tensile, cantilever and compressive loads.

17



17

(c) Guy Strain Insulators

The guy-strain insulators, insulate or isolate the guy wire for corrosion

protection, higher insulation level, clearances for maintenance during normal

operation, or safety to the public or others. It is subjected to tensile and

torsional loads. Fig. (2.7) shows this design.

Fig. (2.7): Guy strain type polymeric insulators.

2.4 WEATHERSHEDS OF POLYMERIC MATERIALS

Polymeric insulators have been in use in outdoor service for about fifty

years. They cover a wide range of materials and formulations. These include

bisphenol epoxy resins which were used commercially for indoor applications

18



18

Polymeric insulators for transmission lines began to be manufactured in

Europe and the USA in the mid 1975 and beyond. In 1977 Hydro Quebec in

Canada installed, on a 16 km section of 735 kV transmission line, 282

composite insulators made by three different manufacturers. This was

followed with a 120 km section using 1100 composite insulators. In addition,

the same power utility installed composite insulators on circuits of 120, 230

and 315 kV transmission lines. Different generic materials were used in the

manufacture of composite insulators. Initially they included Ethylene

Propylene Rubber (EPR) insulators which were made by Ceraver of France

(1975), Ohio Brass of USA (1976), Sedivar of USA (1977) and Lapp of USA

(1980). Silicone rubber (SiR) which was manufactured by Rosenthal of

Germany (1976) and Reliable of USA (1983); and cycloaliphatic epoxy by

Transmission Development of the UK (1977). Currently polymeric composite

insulators are manufactured in several countries worldwide.

Early experience with SiR included Room Temperature Vulcanized

(RTV)-SiR which had a low tear resistance of the weather-sheds.

Subsequently this was replaced with High Temperature Vulcanized (HTV)-

SiR. SiR composite insulators that were used in Germany in 1977 for upto

132 kV, and in 1979 for up to 245 kV [7].

19



19

composite insulators in place of glass. Ohio Brass (1986) introduced an alloy

of Ethylene Propylene Monomer (EPM) and SiR which was subsequently

changed to Ethylene Propylene Diene Monomer (EPDM) and SiR compound

in 1989 [8]. This alloy in a ratio of 10 (EPDM or EPM) to 3 (SiR) provided

the better mechanical properties, such as the stiffness of the EPDM and the

excellent hydrophobic characteristics of SiR. It was reported [8] that one

company has produced commercially with the alloys of EPDM and SiR over

2.5 million (M) distribution insulators, 0.1 M transmission class line post

insulators and 0.4 M suspension insulators which are currently installed in

power systems in different parts of the world. This gives a clear indication of

a wide acceptance of this blend of materials.

In some cases, power utilities are still reluctant to use composite

insulators because of the uncertainty of their long-term reliability, the

unknown life expectancy and the lack of adequate detection technology of

faulty insulators. However there are many organizations including

International Electrotechnical Commission (IEC) and IEEE which have been

attempting to address these problems and develop standards and test methods

for polymeric insulators.

h h h d id h i d l k di d

20



cycloaliphatic and aromatic epoxy resins. For low voltage, outdoor or indoor

applications, additionally high-density polyethylene (HDPE), polytetrafluoro

ethylene (PTFE), polyurethene (PUR), polyolefin elastomers and other

materials are also employed.

SiR was first produced in 1944. When the chain of the dimethyl

polysiloxane is very long (the number of the units of the siloxane is given as

several thousands, the silicone fluid becomes viscous with a gum-like

consistency from which SiR is made by adding fillers and curing agents.

In the compounding of the weather-sheds, fillers are added to enhance

the resistance to tracking and erosion as well as to provide improved

mechanical performance in tensile strength, abrasion resistance, tear strength,

modulus and to reduce flammability. Typical fillers used are alumina

trihydrate (ATH), Al2O3.3H2O or hydrated alumina, and silica (quartz powder)

[10], [11].

It has been reported that weather-sheds of porcelain insulators coated

with a thin layer of RTV-SiR which are being increasingly used world wide in

outdoor substations and on heavily contaminated insulators, gave similar

performance results as compared to SiR sheds [12]. Early guidelines for the

21



2.5 TESTING METHODS OF COMPOSITE INSULATORS

There are several national and international organizations attempting to

develop standards, guidelines and tests for composite insulators. These

include IEEE [14], IEC [15], CIGRE, American National Standards Institute

(ANSI) [16] and National Electric Manufacturers Association (NEMA) etc.

The IEC test [15] has been criticized as being more of a pollution test and not

being an aging test and therefore suggestions for improvements in the test

procedure were made [17], [18]. Most existing laboratory tests for accelerated

weathering are primarily useful for ranking of the compounded materials [71]-

[79].

Only tests in field stations and actual performance on power lines and

in outdoor substations could yield realistic results on outdoor service

performance of such insulations.

In accelerated aging tests in the fog chambers the specimens are

subjected to a simultaneous salt-fog and electric stress. The leakage current,

the pulse current and the accumulated charge are determined during a

prolonged test which can last up to 1000h [15], using an automatic data

acquisition system [19]. Often NaCl is added to the tap water (250 to 300

22



This is highly conductive and hydrophilic which could lead to premature

failure of the insulator being tested. An addition of CuCl2 to the water (1.2

g/m3) obviates the above mentioned problem [20].

The flow rate of the saline water forming the fog and the speed of the

fog droplets impinging on the surface of the polymer have a large effect on the

development of the leakage current even when the electric field stress is

maintained at the same level. The clean fog test method, in which steam is

employed, reflects the contamination in industrial areas away from the sea

coast. However, the dispersion in the test results among different laboratories

was reported to be very large using this method [21]. The clean fog test gives

a lower withstand voltage than in outdoor line performance, because the

insulators are more uniformly coated with the contaminants than in natural

conditions [22].

2.6 TEST RESULTS OF COMPOSITE INSULATORS

It has been shown that tests performed in six different laboratories

using salt-fog and tracking wheel on four different formulations of RTV-SiR

coatings applied to ceramic rods provided consistent results of the ranking of

the materials in terms of leakage current, cumulative charge flow and pulse

23



ultraviolet (UV) radiation on the aging was also included in that test. It was

found that the aging caused erosion and cracks were observed. The EPR

formulations generally performed better than the epoxy resins [24]. 72 kV and

230 kV composite rod insulators made of EPDM, EPM and HTV-SiR were

tested by aging with cement coating and clean fog, salt-fog and cement

coating and salt-fog. Substantial differences in the ability to withstand the

aging were found amongst the different insulator types [25].

It was concluded in [26] that the weather-shed design plays an

important role in the erosion and tracking of the insulator. HTV-SiR

insulators, with 27.6 mm per kV leakage path, showed that dry band arcing did

not develop in the presence of severe salt storms while with 17.3 mm/kV,

large leakage currents developed. A large power utility reported that during a

severe weather condition there were no flashovers in any of their 138 kV (377

units) and 230 kV (1430 units) SiR insulators while there were many

flashovers in their 138 kV and 230 kV EPDM and porcelain insulators [27].

HV porcelain and glass outdoor insulators coated with RTV-SiR

performed better than silicone grease under dc test under salt-fog where dry

band arcing was present [28]. Other metals such as aluminum, stainless steel,

b d i d [29] b f d i f b h

24



surface for improving the contamination performance of outdoor bushings and

ceramic and glass insulators. Full length porcelain multi-core insulators

coated with RTV-SiR had higher flashover voltages than uncoated porcelain

insulators when contamination was present on their surface in the range of

Equivalent Salt Deposit Density (ESDD) of 0.07 to 0.16 mg/cm2.

Fig. (2.8): Dependence of the withstand voltage on (equivalent salt deposit

density) ESDD in SiR and porcelain insulators [3].

SiR insulators had been evaluated in outdoor conditions for nine years

and were found to remain water repellent when either energized or un

25



insulators were almost comparable to the porcelain insulators. The withstand

voltage of SiR insulators decreased with increasing ESDD as shown in Fig.

(2.8).

The withstand voltage of SiR also decreased with increasing non-

soluble deposit density (NSDD) in the range 0.1 to 5 mg/cm2 and increased

with increasing length of the insulator [3].

In another investigation, the ratio of the leakage distance to the surface

area of the insulators was kept constant at 5.6 * 10-3

mm-1

±10% and the

average electric stress was set as that used in practice [26]. It was reported

that the leakage current decreased when this ratio was increased. In RTV-SiR

the leakage current in salt-fog tests increased with increasing electric stress

[33], [34].

Testing SiR on a tracking wheel using a salinity of 1.33 mS/cm showed

that erosion was more severe with positive dc than with ac [35]. The erosion

was confined to the vicinity of the electrodes with dc but it covered a larger

area with ac. There was a larger loss of material with dc than with ac and the

loss was larger at the higher electric field, using 0.83 and 0.5 kV/cm [35].

Studies using electron spectroscopy for chemical analysis (ESCA) on

26



SiR the changes in these elements were not significant. On the surface of SiR

the content of ATH was reduced after 5 yr on the lines. Similar observations

were reported on SiR and EPDM insulators which had been energized at 300

kV. These results were independently confirmed using ESCA after tests in

salt-fog which also indicated a higher concentration of oxygen on the surface

than in the bulk of SiR [36]. It was suggested that this was due to the

crosslinking reactions of the silanols from dry band arcing. The oxidation of

the surface of EPDM and the EPDM/SiR alloy was evaluated by removing a

small amount of the polymer and analyzing it with Fourier Transform Infrared

(FTIR) and X-ray Photoelectric Spectroscopy (XPS) [37].

2.7 RANKING OF MATERIALS FOR OUTDOOR INSULATION

Polymeric materials perform differently according to the severity of the

tests. However, there appears to be a general consensus that HTV-SiR

insulators performed well under severe contamination and usually better than

ceramic insulators [38], [39], [40] and [41]. The withstand voltage of SiR,

EPR and epoxy resin in the presence of pollution was higher than that of

porcelain. Some EPDM insulators (34 kV to 500 kV) performed poorly and

showed punctured holes and damaged sheds. EPR performed better than

i [24] h fl h l f Si f



28



similar performance to that of RTV-SiR insulators which had been exposed to

HVAC and HVDC for many years in outdoor service [12].

2.8 EFFECT OF VOLTAGE POLARITY ON PERFORMANCE

The times to failure of HTV-SiR and EPDM rods at a fixed filler

concentration of either ATH or silica powder during testing in salt-fog, under

ac (60 Hz), and positive dc were similar [29]. For negative dc, the time to

failure was reduced by a factor of 4. The polymer rods were tested in the

vertical orientation and the dc voltage polarity refers to the top electrode. Fig.

(2.9) shows the differences in the cumulative charge in EPDM during

exposure to energized salt-fog for ac, positive and negative dc, and

comparison with HTV-SiR for ac and positive dc [29]. The cumulative charge

and therefore the leakage current was highest for negative dc, and it was

higher for EPDM than HTV-SiR under the same conditions.

At low conductivity (250 µS/cm) fog filled SiR samples had

substantially longer times to failure for ac, positive and negative dc than the

correspondingly filled EPDM samples, while this order was reversed at high

conductivity salt-fog (1 mS/cm) [29].

29



Fig. (2.9): Cumulative charge in EPDM and HTV-SiR rods during exposure

to energized salt-fog showing the differences between ac (60 Hz),

+dc and –dc. Conditions: conductivity of the saline water forming

EPDM (−dc)

EPDM (ac and =dc)

3 SILICONE RUBBER (−dc)

4

SILICONE RUBBER (ac and +dc)

30



2.9 PROPERTIES OF POLLUTION ON POLYMERIC

INSULATORS

It was reported that both sea and industrial pollution produce uniform

contamination layers on the surface of SiR insulators [49]. The salt-fog

produced for un-energized insulators an ESDD of 0.02 mg/cm2 after exposure

to 3 mS/cm salt-fog for ≤2 hours, and 0.02 to 0.05 mg/cm2 when energized at

0.4 kV for 10 and 120 minutes, respectively [49]. SiR insulators from

transmission lines after a number of years in service had typically 8 µm

(ESDD at 0.05 mg/cm

2

) to 23 µm thick of contaminants (ESDD at 0.026

mg/cm2). The nature of the contamination was either carbon dust on the

insulators removed from lines near a highway or dust and bird droppings from

agricultural areas [49].

The dc flashover voltage of SiR contaminated with kaolin

(composition: SiO2 – 46%, Al2O3 – 37%, Fe2O3 – 0.9% [50]), was 15% lower

than with Tonoko (composition: SiO2 – 57~65%, Al2O3 – 14~30%, Fe2O3 –

2~6% [51]), and with Aerosil was lower than both because it absorbed water

and formed a much thicker layer on the surface. After 7 years of service near

the coast no significant difference in ESDD was observed on composite and



32



2.10 ARTIFICIAL CONTAMINATION ON POLYMERIC

INSULATORS

Because of the initial hydrophobic nature of polymeric insulators it is

rather difficult to apply artificial contaminants and to ensure that they adhere

to the surface for the duration of the test. A method of application of artificial

contamination on SiR which was reported to provide a uniform contamination

layer was discussed in [55].

It employs powdered Tonoko [50] which is deposited after spraying the

surface with a fine mist of water droplets and allowing it to dry. Then the

deposited Tonoko is washed off with running tap water. The insulator is then

immersed in the slurry of contaminants and dried. This method was reported

to have been applied successfully to SiR and EPDM insulators [55].

Attempts have been made to coat polymeric insulators with a pollution

layer for testing purposes by first destroying the hydrophobic nature of the

surface by sand blasting or adding wetting agents. The usual procedure to coat

insulators is to contaminate the insulator with a slurry containing water and

NaCl and an insoluble material which is usually kaolin. The insoluble

material content is typically 40 g/l [22]. The slurry is allowed to dry on the

33



2.11 AGING OF POLYMERIC INSULATORS AND MECHANISMS

OF FAILURE

Gorur et al. [41] suggested that aging of polymer insulators in outdoor

service starts with the loss of hydrophobicity due to weathering and then dry

band arcing follows, and in the case of SiR, with a reduction of low molecular

weight (LMW) fluid on the surface. This leads to increased current, increased

surface roughness, depolymerization of the top surface layer, changes in the

structure due to crystallization of the polymer and clustering of the filler and

then tracking and/or erosion failure. X-ray diffraction studies indicated an

increase in the crystallinity of the SiR with aging in salt-fog and dry band

arcing [28].

The difference in the flashover voltage performance for the same

ESDD was attributed to the difference in the solubility of the contaminants.

The ambient temperature has a significant influence on the solubility of the

salts and therefore on the contamination flashover voltage. The solubility of

the salt depends on several factors, the most important of which are

temperature, pH (hydrogen potential) and the presence of strong ionic

components. In outdoor conditions near the coast, highly soluble salts such as

C ( O ) O Cl C Cl C1 Cl d l l bl l h



36



2.12 AGING FROM EXPOSURE TO ULTRAVIOLET RADIATION

Polymeric materials employed to fabricate composite insulators contain

small amounts of compounds such as ZnO2 and TiO2 which absorb UV

radiation and thus protect the material against damage from the radiation of

the sun rays.

SiR filled with ATH (45 to 54%), EPR filled with ATH (56 to 61%)

and SiR filled with silica quartz powder (46 to 50%) were exposed to UV

radiation for 1000 hours and tested on a tracking wheel [62]. The test results

indicated that UV radiation had no effect on the tracking endurance of the

polymers.

Subjecting HTV-SiR, EPDM and EPM to multi-stresses of electrical

(0.5 to 1 kV/cm) and/or mechanical and to UV radiation showed that there was

a synergetic effect between exposure to UV irradiation and mechanical stress.

However, a synergism was not present between UV radiation and electrical

stress when discharges were absent from the surface. When EPDM had no

UV or thermal stabilizers, the advancing contact angle decreased with

increasing exposure time to UV. FTIR spectra showed that the absorbance of

the carbonyl (C=O), the alcohol (C-O-H) and hydroperoxide (C-O-O-H) peaks

increased with increasing time of exposure to UV and there was a correlation



38



Visual inspections of composite insulators were carried out every two

years since 1981 on the 735, 315, 230 and 120 kV lines, Hydro Quebec in

Canada [65]. It was found that most of the problems with composite

insulators could be found by visible inspection from the towers and these

presented the largest percentage of failures. An inspection from the ground

using binoculars was not sufficient.

Electric field testing permitted the detection of non-visible defects

which had occurred at the interface between the fiberglass rod and the

covering polymeric material. It was reported that in the area of a defective

shed there was a decrease in the longitudinal field along the string [65]. Fig.

(2.11) shows the effect on the electric field along the insulator surface when a

defect is present in one of the sheds of an EPDM insulator.

Shed No

16 cm

32 cm

none

antistatic 32 cm

E l e c t r i c F i e l d ( k V / m )

39



2.14 EFFECT OF RAIN ON ELECTRIC FIELD DISTRIBUTION

The axial field distribution along a porcelain post insulator coated with

RTV-SiR changed when artificial rain was applied to it [66]. The sensitivity

of the field distribution and the discharge activity to the precipitation rate of

the rain (0.4 and 1.6 mm/min) was small for conductivities of 50 and 250

µS/cm at low voltage. At high conductivity of the rain and high precipitation

rate, higher fields at the upper sheds were observed [66].

In artificially contaminated SiR and EPR insulators, the phenomenon of

sudden flashover without a prior leakage current was investigated. The

sudden flashover was attributed to the high electric field at the edges of the

dried high resistance regions. When sufficient recovery time was allowed,

SiR did not experience sudden flashover while EPR insulators did. It was

reported that in rain tests, hydrophobic surfaces prevent an increase in the dry

zones and significantly reduce the radial field strength.

2.15 HYDROPHOBIC PROPERTIES AND FLUID DIFFUSION TO

THE SURFACE

In heavily polluted areas, contaminants gradually build up on the

surface of insulators into a continuous layer SiR insulators were reported to



44



A serious problem with composite insulators, however, is their

sensitivity to atmospheric and electrical stresses in outdoor applications. In

contrast to traditional ceramic insulators, composite insulators may be

damaged under combined electrical and atmospheric stress, leading to a

reduction in their useful life. There exist thousands kilometers of overhead

transmission and distribution lines extending through different types of terrain

and environments in the Kingdom of Saudi Arabia. Vast areas of desert, often

adjacent to the sea characterize the Kingdom's climatic conditions and

geography. This type of severity and diversity affects the insulators to a large

extent.

It is clear from this brief review that the long term performance of

polymeric insulators depends on the environmental (specially temperature and

the UV radiations) beside the operating stress levels and need careful

evaluation using laboratory testing as well as field experience history of other

users. This project proposed initial studies towards this goal.

45



CHAPTER 3

EXPERIMENTAL SETUP AND PROCEDURES

3.1 SIGNIFICANCE OF ACCELERATED AGING OF POLYMERIC

INSULATORS

In order to know the satisfactory resistance to weathering, it is

necessary to understand weather factors, and what they can do to various

materials. Climatic conditions around the world are of such diversity that

optimum and economic product design for outdoor use must reflect these

climatic differences. A more realistic, and still reliable design, may be

obtained on the basis of an overall understanding of the range of weather

variables at a specific location under consideration. Such knowledge is needed

both by the designer as well as practicing engineer.

In the world, with widely varying climates and weather conditions, an

insulator in service in the west will experience entirely different climatic and



47



3.2 ACCELERATED AGING CYCLE

For the accelerated aging process as per IEC standard 1109 [15] (for the

non-ceramic (polymeric) composite insulators) tests were carried out on

polymeric insulators made from Silicon Rubber (SiR) and Thermoplastic

Elastomer (TPE), the various stresses to be applied in a cyclic manner, as per

IEC 1000 hours test standard are:

• solar radiation simulation.

• dry heat.

Furthermore, temperature variations may cause some degree of

mechanical stress, especially at the insulator interfaces and also give rise to

condensation phenomena which are repeated several times in the course of a

cycle.

An aging cycle including electrical, temperature and UV radiation

stresses used is shown in Fig. (3.1). Here, each cycle lasts for 24 h and a

programmed change takes place every 6 hours. During the time when heating

is out of operation, the insulators are cooled down to ambient temperature. As

48



Heating (57°C)

Radiation (1 mW/cm²)

Voltage (28 kV)

Time (hours)2~8 AM 8 AM ~

2 PM

2~8

PM

8 PM ~

2 AM

In Operation Out of operation

Fig. (3.1): Accelerated aging cycle.

3.3 DESIGN OF ACCELERATED AGING TEST CHAMBER

For the accelerated aging of nonceramic insulators, as per IEC standard

[15] as discussed in sections 3.1 and 3.2, a wooden chamber was constructed

in our laboratory. The dimensions of the chamber are approximately 120cm

(wide) x 120cm (high) x l80cm (long). Up to 12 post insulators of 28 kVL-L, or

an equivalent number of suspension dead end insulators, can be subjected to

accelerated aging cycle in this chamber. Higher voltages are possible with

slight modifications in the chamber. A schematic diagram of the chamber is

shown in Fig. (3.2a) whereas photo of front view of the chamber with 28 kV

suspension insulators in place is shown in Fig. (3.2b). It is worth mentioning

49



Fig. (3.2a): Schematic diagram.

50



In this chamber, the following instruments/facilities are installed:

i)

UV-A lamps

ii) Polymeric insulator

iii) Electric Heater

iv) Timers

v)

Blower/fan

vi) Power Transformer

vii) UV light meter

i) UV Radiation/ UVA Lamps

UVA lamps are especially useful for comparing different types of

polymers whereas UVB (315-280 nm) and UVC (100-280 nm) are found in

the outer space filtered by earth's atmosphere; germicidal. Because UVA

lamps do not have any UV output below the normal cut-off of 295 nm. The

UVA-340 lamps provide the best possible simulation of sunlight in the critical

short wave length region from 365 nm down to the solar cut-off of 295 nm.

Its peak emission is at 340 nm.

In the chamber, the ultraviolet (UV-A) radiation system duplicates

exposure in the portion of the solar spectrum (300–340 nm) that is responsible

f i f i i l t UV A l Th t d d b



54

C B



C B

220 V, ac

Test

Insulator

220 V / 100 kV

Fig. (3.5b): Transformer connections used for testing.

iv) Heating Arrangement

Since temperature affects the aging of polymeric materials, heat is the

most important stress since the aging rate is accelerated by some factor for

each degree rise in temperature [80]. A 2000W tubular heater is used to

develop heat. A PC based ON-OFF control system is used to maintain a

relatively stable temperature in the chamber. The heat generated by the heater

is uniformly distributed by an axial blower installed inside the chamber. In the

central region of Saudi Arabia, the maximum daytime temperature which

remains almost stable from 1 PM to 4 PM varies during summer months in a

range of 42 ~ 50°C, with around 46°C being the average value. This situation

lasts for six months (May ~ October). To simulate this temperature profile,

the thermostat was set at a temperature of 57°C. This 57°C is selected such

55

This 11°C is also considered to play role in accelerated aging process. Fig.



(3.6) shows the actual variations of temperature on the porcelain and polymer

insulator’s surfaces as well as the UV-A radiation level in Riyadh.

Actual temperature and UV-A radiation level

10

20

30

40

50

60

4 5 6 7 8 9

Months

T e m p r a t u r e ( C )

10

20

30

40

50

60

U V r a d i a t i o n l e v e l ( W / m 2 )

Amb. Temp

Insulator surface temp.(Poreclain)

Insulator surface temp.

(Polymer)

UVA radiation level

(W/m2)

Fig. (3.6): Temperature variation on insulator surface (under no load) and

UV-A radiation level in the Central region of Kingdom (Riyadh).

As per IEC standard 1109 [15] for the accelerated aging cycle, the

temperature rise & fall in the chamber should take place only in 15 minutes.

For this purpose the temperature rise and fall data were measured in the

chamber as well as on the surface of the polymer insulators, using K-type



57



Fig. (3.8): Timer (TM-30A, Kawamura TS, Japan).



73

while the present investigation shows that the surface temperature of



these insulators can increase by 5 to 11 °C above the prevalent ambient

atmospheric temperatures (42 – 50 °C).

2. The SEM analysis revealed that SiR based insulators experience much

higher surface roughness due to aging whereas negligible surface

roughness was observed in case of aged TPE insulators. Similarly the

XPS analysis exhibit much higher decomposition of SiR material than

TPE polymer.

3. Dielectric response of TPE types of insulators also indicates that these

units outperform the SiR type insulator when subjected to the

accelerated aging tests adopted in these tests.

5.2 RECOMMENDATION FOR FUTURE WORK

Since the central region of Saudi Arabia is almost one of the highest

UV-irradiated terrains in the world coupled with high atmospheric

temperatures, therefore, the adoption of polymeric insulators requires careful

selection. In this context, all popular type of insulators including the newly

introduced ones need to be thoroughly and systematically investigated not

di t IEC t l b t d difi d i t l th t t l

58



CHAPTER 4

RESULTS AND DISCUSSIONS

After completion of the accelerated aging test of the SiR and TPE

composite insulators, as per modified IEC 1109 procedure as discussed in

Chapter 3 of this report, various electrical, SEM based optical and visual tests

were performed and the results are summarized and discussed next.

4.1 LIGHTNING IMPULSE WITHSTAND TESTS

In order to compare the effect of accelerated aging, all the laboratory

aged as well as the control (new) insulator samples of each type (SiR and

TPE) were subjected to impulse voltage applications. The impulse generator

was adjusted to produce standard Lightning Impulse (LI) waveforms

(1.2/50µs) of both positive and negative polarities. Fig. (4.1) shows the

positive lightning impulse voltage wave whereas the schematic diagram of this

test set up is shown in Fig. (4.2). The voltage was increased in small steps of



62



100

105

110

115

120

125

130

135

140

Dry (SiR) Wet (SiR) Dry (TPE) Wet (TPE)

F l a s h o v e r

v o l t a g e ( k V )

Insulator (aged)

Insulator (New)

Fig. (4.5): Flashover voltage under 60-Hz AC voltage.

4.3 SCANNING ELECTRON MICROSCOPY (SEM) OF SAMPLES

Small samples (2 mm × 2 mm) were removed from the high voltage

end of each insulator and their surface analysis was performed using type

JEOL JSM-6360-A (Japan) Scanning Electron Microscope (SEM). The

analyses were made in high vacuum mode in order to avoid sample charging.

Secondary Electron Imaging (SEI) was performed to study the surface

morphology at an accelerating voltage of 20kV.



66



Figs. (4.7) and (4.8) show the peaks from the photoionization of oxygen

(O15) and carbon (C15) at 525 eV and 277 eV, respectively. It is also evident

from these spectrums that % share of carbon and oxygen has rapidly increased

from 17.97% and 34.06% to 20.13% and 45.81% respectively in case of SiR

(Fig. 4.7) and from 45.31% and 34.58% to 47.29% and 39.30%, respectively in

case of TPE (Fig. 4.8), due to exposure to UV-radiation and heat. The increase

of C could be from the scission of CH3 bonds and the formation of various

products due to reaction between C and O2 during oxidation.

In these samples, the presence of oxygen detected by XPS both in SiR

and TPE on the new and aged surfaces is attributed to the availability of oxygen

from the additives or from the moisture in the atmosphere or due to oxidation of

the rubber during manufacturing [85]. Peaks of Al are also observed in all

samples as shown in Figs. (4.7) and (4.8). Slight traces of Ti were observed in

case of TPE (new) as shown in Fig. (4.8a) which disappeared due to aging where

instead some traces of Vanadium were detected. This could be due to additives

or any other decomposition process in the material during aging process.

67



(a) SiR insulator (New)

68



(a) TPE insulator (New)

69

Table (4.1) shows the percentage atomic concentration of C, O, Si, and Al

elements in all the tested samples.



Table (4.1): Concentration (%) of elements detected by XPS.

SiR TPEElements

New Aged New Aged

C (0.277 keV) 17.97 20.13 45.31 47.29

O (0.525 keV) 34.06 45.81 34.58 39.30

Al (1.486 keV) 21.69 17.95 17.29 13.08

Si (1.739 keV) 26.28 16.11 -- --

Ti (4.508 keV) -- -- 2.88 --

V (4.949 keV) -- -- -- 0.33

The aged surfaces have different physical, chemical and electrical

properties due to different chemical compounds at different binding energies

(compared to new) because of weathering/photo-oxidation, as observed from

XPS results. This was corroborated by the hydrophobicity change and the

nature of the SEM results observed.

Service experience has indicated that sunlight is an important factor in

70

presence of an allylic group in the polymer backbone. Mere sunlight is not

enough for causing deterioration. Chromophoric groups are also necessary to



absorb the incident radiation and transfer energy to the bond. In polymers,

chromophoric groups are present in the unsaturated structures, such as car-

bonyl groups which are formed during manufacturing. The energy of a photon

of light is transferred to the molecule with resultant bond scission. The

resulting effects may include embrittlement, discoloration, and cleavage of

polymer chains. For this reason, polymers are filled with UV stabilizers and

antioxidants.

Oxidation reactions generally involve a free radical chain reaction.

Some of the main steps in this reaction are as follows:

Heat or Light

RH ⎯⎯⎯⎯⎯→ R (1)

R + O2 ⎯⎯⎯⎯⎯→ ROO (2)

ROO + RH ⎯⎯⎯⎯⎯→ ROOH + R (3)

Heat or Light

ROOH ⎯⎯⎯⎯⎯→ RO + OH (4)

2 ROOH ⎯⎯⎯⎯⎯→ RO + ROO + H2O (5)

71

Radicals are formed during initiation react with oxygen, leading to

chain reactions. The decomposition of hydroperoxides by heat or UV light



(reaction 4) causes formation of alkoxy and hydroxy radicals leading to chain

branching as evidenced by XPS results.

74

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Annex – I

89



90



Annex – II

91



King Saud University, Please return to: Attn: Dr. Yasin Khan

Research Center Electrical Engg. Department

Survey Form Project # 18 / 426 Fax No.: 01-467-6757



I: Polymeric Insulators

Voltage Class Type *Manufacturer

/ Supplier

Material of

the polymer

insulator

No. of years

in service

No. of failures

occurred

Reasons of

failure

13.8 kV

33 / 34.5 kV

* Dead end type /Suspension type /

Line post /Guy strain Insulator

II.

What is the intensity of the solar / ultraviolet (UV) radiations in (mW/cm2)?

III. Any investigative studies carried out internally by SEC on the performance and pollution related problems of polymer insulators inuse?

King Saud University, Please return to: Attn: Dr. Yasin Khan

Research Center Electrical Engg. Department

Survey Form Project # 18 / 426 Fax No.: 01-467-6757 1. Environmental Data of Riyadh



1. Environmental Data of Riyadh

Year Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.

2001 Max. Ambient Tem . C°

Min. Ambient Temp. (C°)

Humidity (%)

Rainfall (mm)

2002 Max. Ambient Temp. (C°)


Humidity (%)

Rainfall (mm)


Min. Ambient Temp. (C°)Humidity (%)

Rainfall (mm)



Humidity (%)

Rainfall (mm)



Humidity (%)

Rainfall (mm)

II. What is the month- wise Maximum intensity of the solar ultraviolet (UV) radiations in (mW/cm2) in Riyadh?

polymer insulators

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