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1304 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 15, NO. 4, OCTOBER 2000

Development of Line Post Type Polymer InsulationArm for 154 kV

Kunikazu Izumi, Takeshi Takahashi, Hiroya Homma, Member, IEEE, and Toshiyuki Kuroyagi

AbstractBased on the results of basic studies on the housingsand FRP cores of polymer composite insulators, a line post typepolymer insulation arm for 154 kV with a truss structure formedby three polymer insulation arm units; i.e., two horizontal unitswith an open angle between them and one suspension unit, wasexperimentally manufactured. Samples of the polymer insulationarm were tested to verify thewithstand voltage performance undera polluted conditions, the impulse and power-frequency withstandvoltage performance, and the mechanical performance by a fullscale test against longitudinal loads.

I. INTRODUCTION

I N JAPAN, while the power demand tends to be densifiedwith the expansion of urban areas, it has become difficult tosecure land for power transmission lines year after year due tovarious restrictions. Overhead transmission lines can be roughly

classified into trunk transmission lines of typically 500 kV and

275 kV and 60 to 150 kV class transmission lines used for power

transmission to distribution substations. To ensure the electric

power transmission to urban and suburban areas, it is necessary

to technically develop compacted 60 to 150 kV class overhead

transmission lines. For this purpose, it is considered very effec-

tive to use more slender towers such as steel pipe type towers

for reducing the tower site area, and to apply insulation arms

for functionally integrating the tower arm and porcelain insula-

tors of presently used transmission lines.In recent years mainly in America and Europe, composite

insulators respectively consisting of a fiber reinforced plastic

(FRP) core, shed housing and metal end fittings provided at both

the ends of the FRP core (hereinafter simply called the polymer

composite insulators) are being used to substitute the porcelain

insulators [1]. The polymer composite insulators are said to be

lighter in weight, better in pollution resistance and more excel-

lent in mechanical impact resistance than the porcelain insula-

tors. So, it is also reported that the polymer composite insulatorsare applied as horizontal insulation supports of a 150 kV class

overhead transmission line [2], as akimbo type insulation arms

[3], or as line-to-line spacers for inhibiting galloping and sleet

jump [4].It can be considered if an insulator arm composed of the

polymer composite insulators (hereinafter called the polymer

insulation arm) is developed and applied, the horizontal distance

Manuscript received December 27, 1997.The authors are with the Yokosuka Research Laboratory, Central Research

Institute of Electric Power Industry (CRIEPI) 2-6-1, Nagasaka, Yokosuka City,Kanagawa Pref., 240-01, Japan.

Publisher Item Identifier S 0885-8977(00)10327-9.

TABLE IREQUIREDSPECIFICATIONS OF LINEPOSTTYPEPOLYMERINSULATION

ARM FOR154 kV

between two circuits of an overhead transmission line can be

shortened to allow a smaller transmission line to be realized.

Samples of a line post type polymer insulation arm for 154 kV

which is considered to be most severe in electric insulation and

mechanical requirements among 60 to 150 kV class polymer in-

sulation arms were experimentally manufactured based on theresults of studies on the insulation characteristics of the hous-

ings for the polymer composite insulators under the polluted

conditions, the mechanical properties of the FRP cores, etc.

This paper describes the experimental manufacture and the

electrical insulation and mechanical performance of the line

post type polymer insulation arm for 154 kV.

II. SPECIFICATIONS

The structure of the 154 kV overhead transmission line con-

cerned and the outline of the required performance in electricinsulation and mechanical forces of the line post type polymer

insulation arm for 154 kV are shown in Table I. The polymer

insulation arms are required to assure a highest phase voltageof 161 kV at the time of single phase ground fault at an equiv-

alent salt deposit density (ESDD) of 0.12 mg/cm as the with-

stand voltage under the polluted conditions, and also to assure

the maximum longitudinal load of 40 kN with the use of an

ACSR 410 mm , power conductor taken into account and the

maximum allowable load of 100 kN obtained by multiplying

the maximum longitudinal load by a safety factor of 2.5.

08858977/00$10.00 2000 IEEE
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IZUMIet al.: DEVELOPMENT OF LINE POST TYPE POLYMER INSULATION ARM FOR 154 kV 1305

TABLE IIRWDT CONDITIONS

Fig. 1. Relation between cumulative charge and weight loss of housingmaterials.

III. BASICELECTRICINSULATIONPROPERTIES OFHOUSINGS

ANDMECHANICALPROPERTIES OFFRP CORES

A. Insulation Characteristics of Housings Under Polluted

Conditions

The electric insulation stresses which can be considered

in the system include lightning and switching surges and

power-frequency overvoltages. Among them, the insulation

characteristics under polluted conditions considered to be most

important for the polymer composite insulators were studied.

To select the housing material of polymer composite insulators,

three kinds of rod samples of SR (silicone), EVA (ethylene

vinyl acetate) and EPDM (ethylene propylene diene monomer)

were tested according to the Rotating Wheel Dip Test (RWDT)

[5]. The test conditions are shown in Table II.

As a result of RWDT for 5000 hours, with any of the samples,no tracking was observed to occur. Fig. 1 shows the relation

between the cumulative charge of surface leakage current and

the weight loss of each sample. From this figure, correlation

was observed between the cumulative charge and the weight

loss considered to have close relation with the erosion of sample

surface. From the test results, SR which was least in weight loss

was selected as the housing material of the polymer composite

insulators.

At the exposuretesting station of CRIEPI, polymer composite

insulators with SR used as the housing material were energized

and exposed for about 8 years. The testing station is located at

about 50 m from the coast at about 20 m above the sea level,

TABLE IIISPECIMENINSULATORS FOREXPOSURETEST

TABLE IVEXPOSURETESTCONDITIONS

and faces the sea on its southwest side. The appearances of the

polymer composite insulator samples and long rod type porce-

lain insulator samples for reference and their specifications are

shown in Table III. The ratio of the creepage distance to the ef-

fective length of the SR housing is about 2.5. For the test, re-

spectively four insulator samples were connected in series and

suspended vertically, being grounded at the top and energized atthe bottom, and an AC voltage of 280 kV was applied.

The energized exposure test conditions are shown in Table IV.

The cumulative 50% and 95% ESDD and standard deviation

on the polymer composite insulators were 0.0139 mg/cm ,

0.107 mg/cm and 29% respectively, which were about the

same as the corresponding values on the porcelain insulators

of 0.0145 mg/cm , 0.116 mg/cm and 30% respectively. The

numbers of occurrences of leakage current over 20 mA and

100 mA in respective years are shown in Fig. 2.From the figure, it can be seen that the leakage currents of

the polymer composite insulators are smaller than those of the

porcelain insulators, and that the numbers of leakage current oc-

currences of the respective current levels of the former are alsosmaller. The difference in leakage current occurrence character-

istics is considered to be attributable to the difference in surface

repellency between the porcelain insulators and the, SR housing

of the polymer composite insulators [6].

The withstand voltages of the polymer composite insulators

were obtained as four-time withstand voltages according to the

solid layer method by wetting after energization [7]. The liquid

pollutant used was a solution with 40 g of a tonoko powder

dissolved per liter of water, and salt was used by 10 g, 40 g and

100 g to achieve ESDD values of 0.06, 0.12 and 0.35 mg/cm

respectively. Since the surface of the SR housing of the polymer

composite insulator has water repellency, the withstand voltage
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Fig. 2. Occurrence frequency of leakage currents on the exposure tests.

Fig. 3. Withstand voltage characteristics of polymer composite insulators andporcelain insulators under artificial polluted conditions.

depends on the drying time after surface polluting [8]. So, the

drying time was kept constant at 4 hours.

The obtained withstand voltage characteristic per 1 m of

creepage distance is shown in Fig. 3. The figure also shows the

withstand voltage characteristic calculated from the Japanese

standard pollution design curve for the porcelain insulatorwith almost the same shape as that of the polymer composite

insulator.

In the design of the required creepage distance of thepolymer composite insulators, based on the withstand voltage

design curve of porcelain insulators under polluted conditions,

a voltage of about 30 kV per 1 m of creepage distance at

an ESDD of 0.12 mg/cm was adopted. This value has an

allowance with the polymer composite insulators, since the

withstand voltages of the polymer composite insulators are

about 1.5 times higher than those of the porcelain insulators as

shown in Fig. 3. Since the required withstand voltage under

polluted conditions is 161 kV, the required creepage distance is

about 5.4 m.

Furthermore, considering that the ratio of the creepage dis-

tance to the effective length of the SR housing is about 2.5,

Fig. 4. Loading and strain measuring positions on insulation arm model.

Fig. 5. Mechanical force test result of insulation arm model.

the required effective length of the polymer insulation arm for

154 kV was set at about 2.2 m.

B. Mechanical Properties of FRP Cores

To optimize the power conductor installation position, i.e.,

loading position, as shown in Fig. 4, two horizontal units with

an open angle of 40 degrees were assumed, and the mechanical

stress on the FRP core was examined for the loading position

A simulated truss structure and loading position B simulated

Lahmen structure.

The samples were of glass fiber reinforced FRP (GFRP),

and had an outer diameter of 7.9 mm and an inner diameter of

4.95 mm. The glass fibers were arranged in the axial direction

only, and the fiber content by volume was about 65%. The ob-

tained relation between applied loads and strains at respective

portions is shown in Fig. 5. From the figure, it can be seen
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TABLE VRELATIONBETWEENORIENTATION ANDSTRENGTH OFGLASSFIBERS

that in the truss structure, an axial force in the compressive

direction acted on the horizontal unit in the loaded side, and

that an axial force in the tensile direction acted on the other

horizontal unit. On the other hand, in the Lahmen structure,

each horizontal unit on the power conductor side and that on

the tower side showed reverse strains, to suggest that a moment

was generated. The breaking load of the truss structure was

2.6 kN, larger than 2.4 kN recorded by the Lahmen structure.From these results, it has been found that the insulation arm

designed with a truss structure is more advantageous. As for

the longitudinal load which is the largest load on the polymer

insulation arm, compressive and tensile loads act equally on the

two horizontal units. So, a GFRP having equal in compressive

and tensile strengths is advantageous. Therefore, hollow GFRP

produced by the filament winding method was used as samples,

to experimentally examine the relation between glass fiber

orientation angles and tensile and compressive strengths. The

glass fiber content by volume was about 65%, and the samples

for a load test had an outer diameter of 26 mm, an inner

diameter of 21 mm and a length of 44 mm.

The obtained relation between fiber orientation angles andstrengths is shown in Table V. The GFRP sample with a ratio

of fibers oriented at 0 degrees to fibers oriented at 90 degrees

kept at 2 : 1 was equal in tensile and compressive strengths, and

the tensile and compressive elastic modulus were 40 GPa. This

GFRP was used as the core material of the polymer composite

insulator for the insulation arm.

IV. STRUCTURE OFLINEPOSTTYPEPOLYMER INSULATION

ARM FOR154 kV

The structure of the line post type polymer insulation arm for

154 kV (hereinafter simply called the polymer insulation arm)is shown in Fig. 6. The polymer insulation arm is composed

of two horizontal units with an open angle for responding to

the longitudinal load and a suspension unit corresponding to the

vertical load. The open angle of the horizontal units was set at

40 degrees as examined in Section III-B, and the open angles

between the suspension unit and the horizontal units were set at

30 degrees considering the vertical load. Each unit was formed

by connecting two polymer composite insulators for insulation

arm shown in Table VI, in series.

The specifications of the GFRP core and the housing were

decided according to the methods described below. The required

axial force of the GFRP hollow core can be obtained from the

Fig. 6. Outside view of line post type polymer insulation arm for 154 kV.

TABLE VITECHNICALPARTICULARS OFPOLYMERCOMPOSITEINSULATOR FOR

INSULATION ARM

following Eulers formula (1) under the condition that a truss

structure is adopted.

(1)

where

: Axial force,: Buckling coefficient,

: Tensile or compressive elastic modulus,

: Geometrical moment of inertia and

: Core length.

In the case of hollow core,

(2)

where , : Outer diameter or inner diameter of core.

On the other hand, the required axial force of the horizontal

units can be obtained from formula (3).

(3)

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Fig. 7. Withstand voltage characteristics of polymer insulation arm underartificial polluted conditions.

where : Maximum allowable longitudinal load of horizontal

units and : Open angle between horizontal units. In the aboveformulae (1) and (2), if we have 2 (general value with

one end fixed), 40 GPa, 2.2 m, 100 kN, and

40 degrees, and if is 80 mm due to the restriction in

the production of filament winding, then is 66 mm. For the

GFRP core, the SR housing had a trunk diameter of 92 mm,

large shed diameter of 176 mm, small shed diameter of 146 mm

and inter-shed distance of 50 mm. The effective length per one

polymer composite insulator for insulation arm was 1.05 m, and

the creepage distance was 3 m.

V. PERFORMANCEEVALUATION OFPOLYMERINSULATIONARM

A. Electric Insulation Performance

The withstand voltage characteristic of the polymer insula-

tion arm obtained by solid layer method is shown in Fig. 7.

The figure also shows the withstand voltage characteristic of a

unit with two polymer composite insulators for insulation arm

connected in series. In the figure, the withstand voltages of the

polymer insulation arm were lower than those of the unit by

about 15% in an ESDD of about 0.12 mg/cm , but exceeded the

specified withstand voltage of 161 kV. Therefore, it was found

that the pollution withstand voltage at an ESDD of 0.12 mg/cm

can be almost satisfied if design is worked out with about 30 kV

per 1 m of creepage distance.

To examine the difference between a polymer insulation armcomposed of 3 units, connected in parallel and an unit in with-

stand voltage, a flashover test according to the slurry method

at an ESDD of 0.35 mg/cm was repeated. Fig. 8 shows the

obtained flashover voltages as normally distributed cumulative

percentages. The voltage of 5% flashover probability obtained

in an slurry test is generally used as the withstand voltage of a

porcelain insulator. The voltage of 5% flashover probability of

thepolymer insulation armwas 164 kV, being lower than 191 kV

of the unit by about 14%. From the result, it can be considered

that the main cause to keep the withstand voltage of the polymer

insulation arm under polluted conditions lower than that of the

unit is the parallel connection of the plurality of units.

Fig. 8. Distribution of flashover voltages.

TABLE VIIIMPULSE AND P OWER-FREQUENCYWITHSTAND VOLTAGES O F

POLYMERINSULATION ARM

Flashover tests of polymer insulation arm samples were

conducted using steep front, lightning and switching impulse

voltage and power-frequency voltage [9], [10]. In the tests,

all the flashovers occurred on the surfaces of the polymer

insulation arm, and the flashover inside the GFRP hollow

core did not occur. Respective withstand voltages obtained by

subtracting double the standard deviation from the obtained

50% flashover voltages of the polymer insulation arm are

shown in Table VII. All the withstand voltages satisfied the

specified value of the 154 kV transmission system. Therefore,

it can be considered that the electric insulation performance

satisfies respective overvoltages if design is worked out based

on the withstand voltage under polluted conditions.

B. Mechanical Performance

To identify the mechanical performance of the polymer in-

sulation arm against the longitudinal load, as shown in Fig. 9,

the insulation arm was placed on a base simulating a tower, and

a load was applied in the longitudinal direction. Two kinds of

tests were conducted. As a static load test, the longitudinal load

was gradually increased. As an impact load test, the load was

gradually increased, and at a predetermined load, a cutting bolt

was momentarily released, to apply an impact load. During the

testing, the displacementat theplacecorresponding to thepower
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Fig. 9. Testequipment andstrain measuringpositions on full scale mechanicaltest.

Fig. 10. Relation between load and axial force in static load test.

conductor installation portion, and the strains of respective por-

tions were measured. The relation between longitudinal loads

and the axial forces calculated from formula (4) is shown in

Fig. 10.

(4)

where

: Average value of strains at three places on the same

circumference,: Sectional area of core and

: Elastic modulus.

The axial forces (#1, #2 and #3) of the horizontal unit in the

loaded side and the other horizontal unit were almost linear

against applied loads. As the axial forces on the horizontal units,

compressive forces acted on the horizontal unit in the loaded

side and tensile forces acted on the other horizontal unit in good

agreement with the basic examination result of Section III-B.

The axial forces of the unit in the loaded side and the other unit

at a load of 100 kN were 140 kN and 150 kN respectively, i.e.,

almost equal. The axial force (#4) on the suspension unit was

found to be smaller than those on the horizontal units.

Fig. 11. Relation between load and displacement in static load test.

The axial force on the horizontal units is calculated to be

1.4 times the longitudinal load based on the formula (3) ex-

pressing the relation between longitudinal loads and the axial

forces of the horizontal units when the open angle of the hor-izontal units was 40 degrees. This value agrees with the axial

force of the horizontal units obtained by the test, and it was ver-

ified that any remarkable bending moment was not generated.

The displacement of the loaded portion was as slight as about

25 mm at 100 kN from the relation between the load and the dis-

placement of the loaded portion shown in Fig. 11. The breaking

load obtained in the test was 150 kN, and the breaking was buck-

ling breaking of the horizontal unit in the loaded side at a portion

near the tower. The buckling coefficient in the formula (1)

obtained from the breaking load is about 2.4. This is conserva-

tive, considering that the general buckling coefficient of 2

with one end fixed used in the basic examination.

On the other hand, based on the strains of the GFRP at the

#1 portion at a load of 40 kN obtained from the static load test

and the impact load test, the amplification factor defined

by formula (5) and the displacement response ratio defined

by formula (6) were obtained.

(5)

where , : Axial forces in impact load test and static load

test.

(6)

where , : Displacements inimpactloadtest and staticload

test.

As a result, was 0.54 and was 0.31. Since both were

less than 1, it was found that the mechanical stress against the

longitudinal load on the polymer insulation arm was larger with

a static load than with an impact load, when a truss structure

was adopted.

VI. CONCLUSIONS

Based on the results of the basic examination concerning

the pollution insulation characteristic of the SR housing for

the polymer composite insulator and the mechanical properties

of the GFRP core, a line post type polymer insulation arm

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for 154 kV was experimentally manufactured. The polymer

insulation arm has an installation length of about 2.3 m and is

formed as a truss structure composed of two horizontal units

and one suspension unit. The maximum longitudinal working

tension is 40 kN. Each unit is formed by connecting two about

1.1 m long polymer composite insulators in series.

The insulation performance under polluted conditions, im-

pulse and power-frequency withstand voltage performance andmechanical performance against longitudinal loads of the exper-

imentally manufactured polymer insulation arm samples were

verified by full scale tests. Furthermore, the design parameters

of the polymer insulation arm for electric insulation and me-

chanical performance were clarified.

ACKNOWLEDGMENT

The authors would like to thank Shikibo Ltd. for the coop-

eration in the experimental manufacture of polymer composite

insulator samples, Nippon Denro Mfg. Co., Ltd. for the cooper-

ation in the mechanical force tests, and Dr. Y. Yoshida, Director

of Yokosuka Research Laboratory, CRIEPI, for his valuable ad-vice on this study.

REFERENCES

[1] H. M. Schneider, J. F. Hall, G. Karady, and J. Rendowden, Nonceramicinsulators for transmission lines, IEEE Trans. on Power Delivery, vol.4, no. 4, pp. 22142221, Oct. 1989.

[2] C. E. Williamson, Transmission line developments up to 150kV ineastern Australia, inIEE Conf., 1988, Publ. 297, pp. 173177.

[3] D. Dumora, D. Feldmann,and M. Gaudry, Mechanicalbehavior of flex-urally stressed composite insulators, IEEE Trans. on Power Delivery,vol. 5, no. 2, pp. 10661073, April 1990.

[4] EPRI, Transmission Line Reference Book, 115138kV Compact LineDesign, p. 29.

[5] IEC 61 302, Electrical insulating materialsMethod to evaluate the re-sistance to tracking and erosionRotating wheel dip test,, 1995.

[6] S.M. Gubanskiand A. E.Vlastos, Wettabilityof naturallyaged siliconeand EPDM composite insulators,IEEE Trans. on Power Delivery, vol.5, no. 4, pp. 20302038, 1990.

[7] IEC 60 507, Artificial pollution tests on high-voltage insulators to beused on a.c. systems,, 1991.

[8] K. Naito, K. Izumi, K. Takasu, and R. Matsuoka, Performance on com-posite insulators under polluted conditions,, CIGRE 33-301, 1996.

[9] IEC 60 060-1, High-voltage test techniquesPart 1: General defini-tions and test requirements,, 1989.

[10] IEC60 506, Switching impulse tests on high voltage insulators,, 1975.

Kunikazu Izumiwas born in Kanagawa, Japan on Oct. 4, 1945. He receivedhis B.S. degree in electrical engineering from Kantougakuin University, Kana-gawa, Japan, in 1968. In 1977, he joined the CRIEPI, Japan, where he has beenengaged in the R&D on composite insulators, surge arresters, etc. From 1989 to1990, he was a Visiting Researcher of the University of Connecticut, USA. Mr.Izumi is a Member of IEE of Japan.

Takeshi Takahashiwas born in Nagasaki, Japan on July 24, 1947. He receivedhis B.S. degree in electrical engineering from Kanagawa University, Kanagawa,Japan, in 1972. In 1977, he joined the CRIEPI, Japan, where he has been en-gaged in the R&D on composite insulators. Mr. Takahashi is a Member of theIEE of Japan.

Hiroya Homma was born in Tokyo, Japan on Sep. 29, 1964. He received hisM.S. degree from Rikkyo University, Tokyo, Japan in 1987 and his M.S. degreein engineering physics from the University of Tsukuba, Ibaraki, Japan in 1989.In 1989, he joined the CRIEPI, Japan, where he has been engaged in researchon polymer insulating materials. Mr. Homma was a Visiting Scholar of the Uni-versity of Connecticut, U.S.A., from 1994 to 1995. Mr. Homma is a Member ofthe IEE of Japan.

Toshiyuki Kuroyagiwas born in Chiba, Japan on Apr. 10, 1967. He receivedhis B.S. and M.S. degree in engineering physics from Yokohama National Uni-

versity, Kanagawa, Japan, in 1991 and 1993. In 1993, He joined the CRIEPI,Japan, where he has been engaged in the research on composite insulators. Mr.Kuroyagi is a Member of IEE of Japan.

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