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1/4

2004 Annual

Report

Conference

on

Electrical Insulat ion and Dielectric Phenom ena

Improvementof Electrical, Mechanical and Surface Properties

of

Silicone

Insulators

M. Ehsani', H. Borsi', E. Gock enbach ', G .R. Bakhshandeh', J Morshedian'

'Iran Polym er and Petroche mical Institute, Tehran, Iran

*Institute of Electric Pow er System s, Division of High Vo ltage Engineering (Schering-Institute)

University of Hanover, H anover, Germany

Material Grade

*SIR Elastmil

R401I60

Vistalon

1500

*EPDM

Ab strac t: The present paper reports about the results of

a study of mechanical and electrical properties of

polymeric insulators. Silicone tubher (SIR), ethylene-

propylene-diene monomer (EPDM) and alloys of

silicon-EPDM are known polymers for

use as

high

voltage insulators. The result of mechanical

measurement shows that the tensile strength, modulus

and elongation of blends enhanced with increase

SIR

in

formulation. It can he seen from the result of dielectric

behavior measurement that dissipation factor tan 6 nd

capacity of silicone rubber improved in the effected of

EPDM in blends. The blends of silicone-EPDM show

good dielectric behavior compare to silicone rubber at

humidity ambient. The new alloy presents excellent

dielectric properties in water and humidity ambient

comparison

to

EPD M, silicone and their blends.

Introduction

Electrical insulators are very important component in

the electrical power system such as sub- stations and

distribution and transmission lines. In the early days,

outdoor insulators were made only of ceramic and glass

materials. Since the 1960s. polymeric insulators were

developed and its improvements in design and

manufacturing, in the recent years have made them

more and more attractive to utilities [ l ] . Polymeric

outdoor insulators also called composite

or

non-ceramic

insulators for transmission lines were developed in the

60's in Germany [ 2 ] and by other manufactures in

England, France,

Italy,

and the US. In Germany, units

fo r field testing were provided in 1967. In the late 1960s

and early 1970s. manufactures introduced

the

fust

generation of commercial polymeric transmission line

insulators [2 ] .

Different polyme rs were used in the manufa cture of

composite polymeric insulators. Initially they included

ethylene prop ylene rubber (EF'R)which were ma de by

Ceraver of France (1975), by Ohio Brass of USA

(1976), by Sedivar of USA (1977) and Lap of USA

(1980); Silicone rubber

SIR)

was manufactured by

Rosenthal of Germany(l976)and by Reliable of USA

(1983); and Cycloaliphatic Epoxy by Transmission

Development of the UK (1977) [2] Virtually, all non-

ceramic insulators consist of three main components:

fiber glass reinforced resin rod system, metal end

Supptia

Wacker-Chemie

Germany

Exxon

Chemical

Belgium

*DCP

I I

Hercules

Inc

USA

98 active

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Several formulations containing silicone rubber and

EPDM were prepared (Table

2).

Silicone rubber was

blended with EPDM and other materials at

180

C in a

Haake internal mixer for 10min at

a

rotor speed

of

100

rpm for preparation alloy of SIR-EPDM and silicon

modified polymer (sample D). The individual

elastomers and the blends were compound w ith DCP in

a

roll

mill

at

room temperature. Vulcanization was done

in

hydraulically operated press at

170

C and

15

bar

for

O min.

TSI

lPaJ

A

7.4

Mechanical Properties

The mechanical properties of samples were determined

according to ASTM D

412

by MTS System Cooperation

MTSIOiM testing machine. The tensile strength,

elongation at break and modulus, were measured by

using

a

500 mm/min cross bead speed. The dumbbell-

shaped specimens were obtained from vulcanized sheet.

Five specimens are measured for each composition.

Dielectric behavior

Dielectric spectroscopy provides information on

molecular dynamics and free charge carriers and it is

sensitive

to

the insulation morphology, i.e., crystalinity,

oxidation, additives and impurities (ions and dipolar

molecules). The measurement of dielectric constants

and dielectric losses in frequency domain help to

quantify the chemical and physical changes in the bulk

of polymer e to aging. Its principle consists in the

measurement of the response of both permanent and

induced dipoles to the application of an external electric

field either in the time domain or more often in

frequency domain. A special dielectric spectrometer

manufactured by Programma Electric AB model IDA

200 was used in this study. By applying good EM

shielding of the instrumentation and the test cells, a test

El

M I Td E2 z

.%

IMPal

[MPal

4

[Mi's]

435 1.7 6.7 350 1 9

B

C

D

ambient temperature

1.3 98 1.5 1.4

117

1.2

2.5 175 1.6 3.07 198 1.63

9.2

330 3.5

9.4

353 3.6

TSI: Tensile strength for virgin samples at ambient

TSI: Tensile strength for heat aged samples at ambient

El: Percentage of elongation at break

for

virgin

temperature

temperature

samples at ambient temperature

El: Percentage of elongation at break for heat aged

MI: Modulus

(100 )

for

virgin

samples at ambient

M,: Modulus

(100 )

for heat aged samples

at

samples at ambient temperature

temperature

624

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3/4

10'

8

6 6

2 4

2

A B C D

Samples

Figure 1:

Comparison of

tbe

value of tem ile strength and modulus for

virgin

and thermal aged

samples

4M)

350

~~

c

3 0 0 -

9 250

c

9 2 W ~

150

1w

50 -

O T

A

B

C

D

Samples

Figure 2: Comparison of the Percentage of

elongation

at break

virgin and

thermal

aged

samples

The mechanical properties of

sample

D without

DCP have also been evaluated and the results obtained

are as follows:

Tensile Strength

=

2.3 MPa

Modulus

(100%)

=

2.3 MPa

%Elongation

=

54

Thus, it was seen that a great enhancement in

mechanical propetties of sample

D

has been reached

after curing.

Dielectric behavior

studies

Dielectric spectroscopy is based on the interaction of

electromagnetic radiation with the electric dipole

moments of the material under test. The frequency

range of the radiation is between IO Hz and about

10

Hz

Above 10

Hz

in the infrared optical and

ultraviolet region, the absorption and emission of

radiation is due to changes in the induced dipole

moments, which

are

dependent

on

the polarizability of

the atoms or molecules. At lower frequencies the

contribution of the induced dipole moments becomes

small in comparison with thet of the permanent dipole

moments of the system. Results of frequency domain

measurements of blend of silicone rubber-EPDM and

new blend sample (D) at 27 C

are

illustrated in Figure

3 and 4.

Absorption of water sometimes has caused

seriously affects the dielectric properties of polymeric

insulating material. Permittivity of polymers increases

with increasing water absorption. The samples (A, B,

C

D) are aged by immersing in distillated water at mom

temperature for

1000

h

with

mm

in thickness. Results

of frequency domain measurements of samples after

immersion w ater aging are shown in Figures 5.

0

0.01

IQ

B

0.001

o.Oo01

0.01 0.1

1

10 100 1000

Frequency Hz)

Figure 3: tan

of

the new samples

over

he

frequency

It can he seen from Figure 3 that sample

D

shows a

low

value

of tan compared to other blends. The value

of tan S increased for samples

(A,

B, C) after immersion

water aging (Figure

5 .

It means that samples have

absorbed water during aging. It can

also

be seen from

Figure 5 that sample D has the lowest value of tan 6 in

comparison to other samples. Figure 6 shows the results

of frequency dom ain measurements for humidity aged

samples. The samples were

exposed

to

90-95

humidity for 1000 h at m m emperature . The thickness

of samples was

I

mm.

625

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I+A + B +C

X d

Conclusion

New

polymeric alloy for outdoor use of high voltage

insulator has been introduced and its electrical,

mechanical and electrical properties

are

compared

to

already known outdoor com posite insulation in different

conditions.

The mechanical properties such

as

tensile strength,

modulus, and elongation at break are. improved

compared to known polymeric insulators.

The electrical properties such as dissipation factor

and permittivity are also enhanc ed.

Acknowledgments

The

authors thank GE Energy Management services

Gm bH and Programma Electric

AB

for letting

us

to use

IDA 200 Insulation Diagnostic Syste m and the Ministry

of

Energy of Iran

for

supporting this project.

References

[I] Hackam, R. Outdoor High Voltage Composite Polymeric

Insulators ,

E E E

Trans. Dielecuics EL 6, 1999,

6 .

(

5 . 557-

585

Hall. J.F. History and Bibliography of Polymeric Insulators for

O u td m Applications .

E E E

Transactions. Power Delivery.

1993.8. (1).

376-385

Gubanski. S . M. Modern O u td m Insulat ion

-

Concern and

Challenges ,

14 th International Sympo sium On High Volmge

Engineering(1SH). DelftINetherlands. 2003

Bernstorf, R.

S.;

Zhao T, Agin g Tests of Polym ric Housing

Materials for Non-Ceramic Insulators , IEEE Electrical

Insulation

Magazine. 1998. 14. (2). 26-33

Chemey.

k

Kim S . H.; H a c b m R. Hydrophobic Behavior of

Insulators Coated with RTV

Silicone

Rubber , IEEE Trans: El,

1992,27,610-622

[2]

[3]

[4]

[ 5 ]

Author address: Moiteza Ehsani, Institute of Electric

Powe r Systems, Division

of

High Voltage Engineering

(Schering -Institute), University of Hannover,

CaUinstr. 25A, D-30167 Hannover, Germ any

Email: ehsani@si.uni hannover.de

4.5E-ll

4Ell

,

35311

3E-I1

0.01

0.1 10

loo

IMX)

frequency Wd

Figure 4

Capacitance

of

new samples (A,B,C,D)

over

the frequency

1

0,1

U0

0,Ol

0,001

0 0001

1

0,Ol 0,1

1

10

100 loo0

kW Y (W

figure

5:

tan

6

of the water aged samples over the frequency

0.1

0.01

U0

1

0.001

0.01

0.1

1 10 100 1oOo

FhluencY

Hz)

El- : an 6 of

the

humidity aged samplesover the frequency

626

mailto:ehsani@si.uni-hannover.demailto:ehsani@si.uni-hannover.de