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Evaluation Methods of Polymer Insulators

under Contaminated Conditions

R.

Matsuoka,

Fellow

IEEE,

K

.Naito,

Lije

Fel low

IEEE,

T.

Irk,

Senior

Member IEEE and K. Kond o, Member IEEE

Abstract Although polymer insulators generally show

superior inaulation performance under contaminated and

wetted

conditions

due to hydrophobicity on the i r ~U rtace .

Owmg to shortage

o f

their field experience,

anti-amtam ination design criteria

are

not yet established.

Presently the same design criteria for ceramic insulators

are mostly adopted by cons idering th e hydrophobicity as

safety margin.

In order

to

establish rationalized insulation design

criteria for polymer insulator^. we made fundamental

investigation. We found ou t 1) Roughly t w o t imes

heavier contaminant deposit on hydrophobic polymer

insulators than pornla in under s low deposi t

conditions,

while such Me re nc ss become

smaller

under rapid depoait

conditione like typhoon.

2) In

spite of smaller leakage

cumnta

on hydmphohic polymer in~uhtcm, stiff power

8ource

ia sti necessary for evaluating their

contamination

hshover vol tages.

3)

Contamination flashover voltages

of hydmphohic polymer ineulat~mshould be evaluated

und er heavy wetting conditions. Combined t e s t s under

heavy fos and

rain

conditions may be good candidates for

eva lua t ing polymer insula tors .

Index

Te-

Accumulation 1Contaminants, Contamination

Flashover, Evaluation Methods, Plasbover

Voltage,

Hydrophobicity, Leakage Current, Polymer Insulston, Power

Source, Silicone Rub ber,

Wetting

Conditions

1. INTRODUCTION

Polymer insulators generally show superior

insulation performance under contaminated and wetted

conditions compared with conventional ceramic insulators

like porcelain or glass insulators. Such superior

Derformance is fundamentallv owing to hydrophobicity on

In order to establish rationalized design and maintenance

criteria for such insulators, we have conducted fundam ental

investugation works and some results are shown here.

11. ACCUMULATION OF CONTAMINANTS

Contamination flashover voltage o a hydrophobic

polymer insulator is also similarly influenced by

contamination degree with the case of porcelain insulators,

that

is,

almost proportional to 115 power

of

SDD(Salt

Deposit Density)[ I].Heavier deposit o contaminants on

hydrophobic polymer insulators compared with ceramic

insulators

has

been measured at various

sites

12)

-

C41

.

Recently we have also made comparative measurement

on

porcelain and polymer insulators at the site 50m from

seacoast located in the suburbs

of

Osaka[site

A].

Results are

shown in Tables and 2. Such heavier deposit

o f

contaminants is partly attributable to oily surface conditions.

Once contaminan ts deposit on such oily su rface, they are not

easily removed by wind

or

rain due to adhesive nature

of

their

surface. Under rapid contam ination conditions like typhoon,

Table 1 ESDDRatio of Polymer to Porcelain

Maximum

I

7.44

I 8.17 I 4.79 8.17

Minimum

I

0.81 0.93 I 0.67 0 67

Measurement period: March 1998 to January 2002.

ESDD measured on 3 month exposed insulators.

-

. .

their

surface. Hydrophobicity,

is,

however, Sometimes 10s Table 2 ESDD Measurement Results under R a i d Contamination

by surface discharge or heavy wetting, and recovered with

time by the diffusion of low molecular weight silicone onto

the surface from the bulk

of

silicone rubber. Polymer

insulators are made of organic materials and so ageing change

of

surface conditions is not avoidable. In addition, polymer

insulators are quite new comers, and so field experience

on

contamination performance of these insulators is limited.

Contamination tlashover/withstand voltage test methods of

these insu lators in laboratory

are

not yet established.

R.

Metsuoka ie with Chubu University 1200 Matsumato-do. Kesugai.

Naito

la

with Meija University, 1-601 Shiogamaguchi,

Tempaku-ku.

T. Iris iE \ntb NOK Imulatori, Lld I I 5 5 Tag-, Fulaebm

,

Komaki. 185-8566.

K. Kondo e;

\ntb

NGK

n~ulDtors.

id.

I 155

Tag-, Fulkboi,

Komaki. 485-8566,

Aiehi,487.8501. Japan

e-mail:mst4uo~se.chubu.aedp)

Nagoya 468-8502 Japan (wmsil:

kmit&%mfs.meijwu.ae.jp).

1ap.n

(e-mail:ir*lak@n&k.~.jp)

lopsn s-mul:

kavbk@gkOojp)

Condi t ions

0-7803-7525-4/02/ 17.00 2002 IEEE.

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oily substances are washed

off

by heavy rain and/or strong

wind, and

so

difference in contamina tion degree between

porcelain and polymer insulators becomes smaller. So,

dependin g on the critical contam ination conditions in

a

given

site, rapid or slow accumulation

of

contaminants, a pertinent

correction factor for the design contamination degree of

polym er insulators at a given site agains t the refe rence

contamination degree measured on conventional porcelain

insulators must

he

selected for rationalized design of

hydrophobic polymer insulators. Influence of insulator

diameter on deposit o f contamin ants on polymer insulatoi

surface was investigated under rapid contamination

conditions at sites A and

B.

Site

B

i s located near seac oast in

Okinawa island. Results are shown in Fig.1. Reduction

in

ESDD can be found with the increase of average diametei

also in the case of polymer insulators

1.2 r

I

2

3

4

P a l p e r

Lang-md

R eg r e ss i o n c u w e

/

o f

p o r c e l a in i n s u l a t o r s

12615W 7 350-

980-

126150

12

600

1680

166170

9

450 1602

166170 7 350

1246

9

0.2

-

5

6

7

Porcelain

standard

Disc

166,

136137.5

430 1648

166,126135

365

I445

615

(LonglShon)

515

LonglShon)

2541-

(146)

280

0 1

0 200

400

600 800

Average

diameter. D. rnm

Fig. 1 Influence of Average Diameter of Insulator on

Contamination Degree under Rapid

Contamination Conditions

111. EFFECT

OF

POWER SOURCE

ON

WITHSTAND VOLTAGE

In the case o f porcelain/

glass

insulators, heavy

leakage currents flow along the surface of specimen

insulators in contam ination flashover/ withstand voltage tests

especially

ust

before flashover, and

so

stiff power source is

specified for such evaluation ests[fi].

In the case

of

hydrophobic polymer insulators, however,

relatively smaller magnitudes of leakage currents have been

measured both in fields and in laboratories.

So,

it is

expected that stiff power source may not be necessary for

flashover/withstand voltage tests

of

contaminated

hydroph obic polymer insulators. We examin ed the effect of

stiffness of power source on contam ination flashover voltages

of

hydrophobic polymer insulators using a stiff and a weak

power

sources.

A . Test Method

Comparative flashover voltage tests were conducted hy

using the two pow er sources shown in Table 3.Dimensional

particulars of specime n insulators are shown in Table

4.

Table 3 AC Power Sources for Insulator Contam ination

Tests

Power S a u n e A

I

PowerSourceB

I hour) (Continuous)

nmary

(1

hour) (Ihour)

Y mpedance : 7.0

Rated Voltage : 0kVl26.3kV

RatedCapaciiy : I40kVA

Impedance

:

2.03

(

1

hour)

Table 4 Dimensional Particulars

of

Specimen Insulators

Speeimen Shed Dial EffectiveLength

NO. I Shedpitch No'ofSheds

[

(ConneetionLength)

[

wgeDirtance

hed Shape

pecimen

Insulators

I

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Tests were conducted according to the clean fog method

specified in IEC Pub. 507 except for m odified fog density and

special pretreatment for uniform contamination layer on

hydrophobic insulator surface based on our investigation

results

[ I ]

Heavier fog such as 13-15

g/m

gives much lower

flashover voltages to hydrophobic polymer insulators

compared with the case of thin fog conditions used for

ceramic insulators. Special pre-treatment was conducted in

order to get uniform and continuous contaminant layer on

hydrophobic insulators simulating actual contaminant deposit

conditions in fields. Time variations o f fog density in both

chambers for conventional thin and special dense fogs are

shown in Fig.

2.

In case of polymer insulators, however, discernible

differences cannot be found in the flashover voltage between

the two power sources under the contamination conditions of

0.03 and 0.12 mp/ cm2 while significant difference can be

recognized between the two power sources under heavy

Contamination conditions of

0.5

mg/

cm2.

1.6

q

1.4

1.2

m

.

h 1.0

1

0.8

0

10

20 30 M 50

60

0 1 0 2 0 3 0 1 0 y 1 6 0

Tim b e . min

Tim Lapse.

min

( i

1 Chamber A ii) Chamber B

Fig. 2 Time Variation of Fog Density

B. Test Results

Some typical leakage current and applied voltage wave

forms at the time of flashover by Power Source

A

are shown

in Fig. 3. In this test facility, in order to minimize the

voltage drop of power supply system, protecting resistor of 25

or 50 kn was inserted between testing transformer and

specimen. So short circuit current was limited to around 1 A.

In the case of porcelain insulators, leakage current increases

gradually to flashover while polymer insulators flash over in

shorter

periods

after start of increase of leakage current

especially in the case of light contamination conditions.

Comparative

50

flashover voltages obtained by Power

Source A referenced to the corresponding flashover voltages

obtained by Power Source

B

are shown in Fig. 4. As

expected, higher flashover voltages were obtained by weak

Power Source A in case

of

porcelain insulators irrespective of

contamina tion degrees.

02

0

Fig.4 Comparative 50% Flashov er Voltage

by

Two

Power Sources

IV. CONTAM INATION TEST METHODS

In case of artificial contamination tests of ceramic

insulators, artificial fog is specified for wetting the

contaminated insulators in solid layer methods since it gives

lowest flashover/ withstand voltages. In case of

hydrophobic polymer insulators, however, heavy wetting

conditions such as heavier

fog

than conventional

fog

used for

ceramic insulators or rain, give lower flashover/ withstand

voltages

[SI

171. In order

to

find

out

the severest w etting

conditions giving the lowest flashover voltages for

hydroph obic polyme r insulators, we investigated the effect of

rain conditions on flashover voltages of polymer insu lators.

A. Test

Methoak

Based on the investigation results explained in the form er

section, we installed a new power source stiff enough for

contamin ation tests [ 8 ] [ 9 ] .

(

i

Pomelain/SDD :0.07mg/cm2

( U )

Polymer/SDD 0.03

mg/cmz

id Polymer/SDD 0.6mg/cm2

Leakage C urrent and Applied Voltage at

the

Time of Flashoverig.3

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Such lower flashover voltages are attributable to the water

streams flowing down along individual shed s as illustrated in

Fig. 9. Again much higher ratios were obtained on the

Such

explained by the saturation of salt soluble into the water film

deposited on the surface of specimen insulators under heavy

fog conditions. Enough quantity

of

water

is,

however,

supplied under simulated rain conditions even with the SDD

of

0.5 mg/cm2. Relationship between

SDD

and flashover

voltage may be explained qualitatively by two curves shown

in

Fig. IO

insulators contaminated with SD D of 0.12 mg/ cm2.

different ratios between

0.12

and 0.5 mg/ cm may be

2

ri

I

, I

0.03

0.12

0.5

SDD. mgIcm2

Fig. 10 Contamination F.O.V. Characteristics

40

of A Polymer Insulator

V. CONCLUSIONS

Based on our investigation results, the followings should

he taken into consideration at the time of evaluation and

design

of

polymer insulators

I)

Heavier contaminant deposit should be considered on

hydrophobic polymer insulators compared with

conventional ceramic insulators.

(2) A stiff power source should be used for evaluation of

contamination flashover/withstand voltages of

hydrophobic polymer insulators, especially under

heavily contaminated conditions,

in

spite

of

smaller

leakage currents measured both in fields and

laboratories.

(3)

Contamination flashovedwithstand voltages of

hydrophobic polymer insulators should be evaluated

Fig. 7 Com parative Flasho ver Voltages under heavy wetting conditions. Both heavy

fog

and

simulated rain tests mav be

eood

candidates for standard

contamination flashoveriwithsland voltage test methods

for hydrophobic polymer insulators.

VI. REFERENCES

Il l

K. Naito, K. Immi, K.T h u nd R. Malsuoka, Performance of

Comwsi te lnsulalom

under Polluted

Conditions. ClGRE Session

f

i

) S t r a i g h t S h e d s f

ii 1

A l t e r n a t e S h e d s

PapeiNo.

33-301, 1996.

H. l rnapawa

R.

Matsuoka S .

110.

K. SAanishi. K. Kondo. N. Okada21

,

~ ~~

.

~

.

and T.Yonezawa,

Comparative Contaminatio Degrees

on

Porcelain

and Sil iw ne Rubber

Insulators

in Fields, ClGRE SC33 Colloquium,

Paper No.

3 3 - 4 3 , Toronto,

September IW7.

Y. Hi&whimori, 2. akao, S. Nishimura, J. X. Zhu, 2. Iha,

T.

Tmaki,

I. Kat. R. Kimata T.Mugushima and T. Kohayashi, Studies on Salt

Conrnminalian and

Leakage

Current of Silicone Rubber InsuIafors,

ICE. pp.744-748, Beijing, China,

1996.

K.

Kondo, M .

Ishiwari, S.

Ito,

I.

Irie, Y.

Suzuki and K.

Amkawa.

Pollution Performance of Polymer Insulaon under The Marine

Conditions in

Japan. ISH-2001.

Paper No. 5-19, Bangalore, India,

August 2001.

IEC Pub.

507.

Ar t i f ic ia l

Pollution Testson

High-Voltape

lrrsulamn

lo be Used on

A .

C. Systems,

1991.

A. de la and

R.

. Gorur. Flashover of Conlaminated Nonce ramic

Outdoor lnsulator~n A

Wet

Alrnosphcre,

IEEE Trans. On DEI, Vol .

5,

No. 6,

December

1998.

M . Ishiwirri. S. 110, K. Arakawa, T. Nakachi and K. Kondo. Various

Altificial Contamination Withstand Voltsge Test Methods

and A

Fig. 8 Dripping of Water at the Tips of Sheds

(Precipitation: 4mmlmin)

[3]

141

51

16

[7]

q

(

i )Vertical Installation

( li1

Horizontal lnatallation

Fig. 9 Flashover Paths in Simulated Rain Tests

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Comparison of Their

Results

on Polymer and Porcelain Insulalops,

paper presented at the I

I ISH, London

U ~ U S I1 .

[SI N.0 K. Ikeda, S Sumi, R Matsuaka K. Kondo and S Ito,

Contamination Withstand Voltage

Chamcleristics

of Hydrophobic

Polymer Insulators under Simulated Rain Conditions, Paper to be

presented

at lSEl

in

Boston,

April 2002.

K. Ikeda, N. Okada, S Sumi,

R.

Mauuoka, K. Takemato, T. Ito, T.

Ono

and

Y.

Komiya A New Power

Source

for

Insulator

Contamination Tests, h f the Twelfth Annual Conference o f

Power Energy Society, IEE o f Japan,

Vol.

B.

P a p

No. 493, 2001

( In

Japanex ).

[ 9 ]

VII. BIOGRAPHIES

Rymuke Mabuoks SMW- F96)

was

born

in Gifu Prefecture,

J a m

n

1941.He received the BS, MS and the Ph.D. degrees, dl in Elsuical

Engineering fmm the Nagoya University in 1964 1966 and 1994,

respectively.

He

joined NGK Insulators Ltd. in 1966. He served asGeneral

Manager of NGK High Voltage

Laboratory.

He w e d also as manager of

Insulate(.

Engineering, in h k c nsulators Inc. fmm 1981 to 1986. He

retired NGK an d joined Chubu University as a full time mfessor

in

1598.

Pmf. Mauuoha is a Member o f C E R E and IEE of

Japan,

Katsuhiko N d o M66SM8C-FW)

was

born n Aichi P refenm,

Japan,

in

1934.He received the EIS, MS and the Ph.D. de- all

in

Electrical

Engineering fmm the Nagoya University in

1958,

1 0

and

1976

respectively. He oined NGK Insulators Ltd. in 1964. H e

served as

General

Manager of Design Deparunent,G e n d Manager

of

NGK, High Voltage

Laboratory, and later

as

Executive Chief Engineer of Power Business

Group

of

the Company. He joinedNagoya lnstiate afTechnalogy in 1991

BS a

full-time

Professor. In 1998, he &red

fmm

Nagoya Institute o f

Technology and joined Meijo University

as a

ful l-ti m Fmfessor. Prof.

Naito is a Member o f CIGRE and B Fel low of

IEEE

of U.S.A. H e is a

Member of Insulator and Lightning Arrester Subso mm inee of IEEE.

Takarbl

l r i r

SM91) as born in Tottori Prefecture,

Japan.

in 1944.He

received the BSc. and Ph.D.

de

oth in elenrical engineering from

Yokohama National University in 1968 and 1995, respectively. In 1968 he

joined NGK Insulators Lid. He is now the General Manager of NGK High

Voltage Labamtory, Power Buincss Gmup. His

f ields

o f interest include

insulator contamination, ightning

arrester

and in sulation smength o f large

air

W .

Kunhki

Kondo ( M Y 8 ) WBS

barn in Aichi

Prefechue,

Japan

in 1967.

He received the

B. Sc.

M.

Sc.

and Ph. D. d e p s n electrical engineering

fmm Nagoya lnstitutc

of

Technology in

IWO,

IW2 and 1997. respectively.

In

1992

he joined NGK Insulators, Lld. He has

been

engaged in rereareh

of

insulator commination. He

is

now a Supervisor of NGK High Voltage

I.aboratory, Power Business Gmup.

2202