First Application of 66-kV Outdoor Terminations with
Composite Hollow Insulators for XLPE Cable
by Takeshi Goto *, Yoshikatsu Hori *, Masato Asakawa *,Masahiro Suetsugu *2 and Tokui Yonemura *3

Composite hollow insulators have a number of advantages over porcelain insulators, including lighter weight, better anti-pollution and anti-explosion properties,and easier construction. They are therefore being considered for use with outdoor terminations
installed on towers for branching.
Tokyo Electric Power and Furukawa Electric have jointly developed a 66-kV outdoor termination with composite hollow insulators, and have used it on Tokyo Electric Power's Oihama line-the first such application in Japan.
This paper outlines the performance specified for the 66-kV termination, together with development tests and evaluation results, and the specifications of equipment supplied to the Oihama
Line.

ABSTRACT1.

INTRODUCTION

Because of their long track record, porcelain insulators are
the mainstay of outdoor electrical insulation applications.
But over the past 20 years on-going improvements in thecharacteristics of silicone rubber and other polymer materials have led to increased use of composite insulators,
which are lighter in weight, mechanically stronger and better in anti-pollution properties, as interphase spacers andstrain insulators. More recently hollow type composite
insulators have also been used for bushings in gas-insulated equipment.
The main structural elements of a composite hollow
insulator is an FRP tube having high mechanical strength,
covered with a silicone rubber housing or shed having
superior weather-resistance and electrical insulation properties, and with metal fittings strongly fastened at bothends.
Composite hollow insulators are superior to porcelain
insulators in several respects, including lighter weight, better anti-pollution and anti-explosion properties, and easierassembly. Active consideration is therefore being given to
their introduction when installing outdoor cable terminations on towers.
This paper outlines the process of developing an outdoor termination with composite hollow insulators,
describing artificial pollution tests using samples, development specifications, development and evaluation test
results, and the specifications of the products installed.
* Tokyo Electric Power Co.
*2 Power Cable Engineering Dept., Power Cables Div.
*3 Energy Transmission Research Dept., Ecology and Energy
Lab.

2.

COMPOSITE HOLLOW INSULATORS

Composite hollow insulators--also known a silicone rubber
or polymer insulators--are usually made of an epoxy-type
FRP tube manufactured by a filament winding technique,covered with a silicone rubber housing or shed and withmetal fittings fastened at both ends. The FRP impartsmechanical strength, while the silicone rubber provides
weather resistance and external insulation performance.
Filament-wound FRP is particularly strong against innerpressure, and the silicone rubber owes its anti-pollution
properties to its hydrophobicity and low molecular weight(LMW) effects. As would be expected from the constituent
elements used, unit mass is low--only about 20-30% thatof porcelain insulators.
In recent years composite hollow insulators have been
increasingly used in Europe and the U.S. as bushings forgas circuit breakers.

3.

ARTIFICIAL POLLUTION TESTS ON SILICONE RUBBERTokyo Electric Power and Furukawa Electric have carriedout a joint program of research with a view to using thesecomposite hollow insulators in outdoor terminations 1). Oneof the primary advantages of these insulators is theirresistance to pollution. The present situation is as follows:• There are few examples of their use in working lines,
so field test data is inadequate;• The artificial pollution test methodology now in use
was developed to evaluate porcelain insulators, so
there is much room to doubt that evaluations are53

made under conditions that reflect the special characteristics of composite hollow insulators and the silicone rubber housings.
In our development testing, we have conducted artificialpollution tests using sample tubes to control the adherence of contaminants while utilizing the hydrophobicity ofsilicone rubber, and have found that 2):• As in the case of porcelain insulators, outer diameterhas an effect on withstand voltage characteristics
under pollution;• The withstand voltage under pollution decreases witha rise in the equivalent salt deposit density (ESDD) on
the surface of the sample, but when ESDD exceeds
1.0 mg/cm2 no further decrease takes place.
We therefore came to the conclusion that for composite
hollow insulators with an average outer diameter of 260mm (hereinafter referred to as 66-kV rated), a creepage
distance of more than 33.25 mm/kV would be ample even
if ESDD exceeded 1.0 mg/cm2.
For 66-kV composite hollow insulators for outdoor terminations, we may calculate the creepage distance required
using 69 kV, the target pollution withstand voltage, by33.25 mm/kV x 69 kV = 2295 mm

4.

DESIGNING A TERMINATION WITHCOMPOSITE HOLLOW INSULATOR

The design specifications for the composite hollow insulator termination were arrived at by analogy, to maintaincompatibility with existing porcelain insulators.

face creepage distance of the composite hollow insulator-using the results from tube sample tests described above
we may set the lower limit for creepage distance using
data for an ESDD of 1.0 mg/cm2, no matter how high theESDD of the region may be. By this line of reasoning
creepage in regions with ESDD of over 0.06 mg/cm 2(equivalent to heavy or very heavy pollution) is shorter by
20% or more compared to porcelain insulators.
The present situation, however, is that:• There is no clear correlation between tests on sample
tubes and long-term anti-pollution performance in thefield;• Most examples of creepage distance design forequipment used in composite hollow insulators in thepast have been established based on creepage distance designs for porcelain insulators.
Accordingly the following procedures for creepage distance design were established, erring on the side of safety:• The creepage distance for 66-kV rated terminations
with composite hollow insulators was establishedaccording to "Anti-Pollution Design for Substation
Equipment" 6), which is the basic design standard forporcelain insulators;• Notwithstanding the above, to take advantage of thepossibility of reduced creepage distance suggestedby the sample tube tests, the track record resulting
from actual operation should be taken into account toallow future reductions in creepage distance of up to
5% from the porcelain design described above.

4.1 Electrical Design
The required levels of initial electrical performance andlong-term loading were determined in conformance with
JEC-3408 3), and with Electrical Standards A-263 4), which
are based on it.

5.

4.2 Mechanical Design
The mechanical properties of the insulators under bending
are determined on the basis of the levels of wind pressure, inner pressure, seismic force and short-circuit electromagnetic force anticipated during operation. But since
the composite hollow insulator is lighter in weight thanporcelain, the load with respect seismic force resulting
from the weight of the insulator itself is reduced.
By selecting the appropriate inner FRP for the composite hollow insulator at the design stage, it is possible toestablish mechanical strength that is broadly in accordance with the required specifications.
Mechanical strength for the composite hollow insulator
is set so that the maximum designed cantilever bending
force and the maximum designed inner pressure satisfy,
respectively, the requirements for maximum mechanicalload (MML) and maximum service pressure (MSP) as set
forth in IEC-61462 5).

5.1 Withstand Voltage and Long-Term Voltage Tests
As can be seen from Tables 2 and 3, both the initial withstand voltage tests and the long-term (6-month) voltage
tests were satisfactory.
The long-term voltage tests were carried out over a 6month period at a test site in a seaboard industrial area onan outdoor termination located about 10 m from the shoreline. The voltage applied was 1.44 times 66-kV cable voltage to ground. Snowfalls also occurred during the tests

4.3 Anti-Pollution Design
With respect to anti-pollution design--that is to say the sur-54

EVALUATION TESTSTable 1 shows the evaluation tests, which were carriedout using a prototype outdoor termination designed for
medium pollution (ESDD of less than 0.6 mg/cm2).

Table 1

Specifications of terminations subjected to electricalperformance tests
XLPE cable specifications

66 kV

Conductor size

Insulation thickness

2000 mm210 mm

Composite hollow insulator specifications

Prototypefor 66 kV

Length (mm)ID (mm)1100

198

Creepage distance (mm) Weight (kg)2390

Furukawa Review, No. 20

172001

but on completion of the tests no degradation of the housing was observed. After the long-term voltage test, the terminations also passed a test to evaluate residual performance, under the conditions shown in Table 4.
5.2 Outdoor Exposure Tests
Outdoor exposure tests of the bare composite hollow insulator were carried out using insulators having the same
specifications as those subjected to the 6-month voltage
test. The applied voltage was 53 kV. The test was carriedout to check for water penetration to the interior of thecomposite hollow insulator, and to evaluate the conditionof the housing.
The inside of the composite hollow insulator was filledwith silicone oil and the oil was periodically sampled andanalyzed, and although an increase in moisture content
was observed, there was a tendency to saturate 1), and it
was confirmed that the level was not such that its electrical performance was affected.
The hydrophobicity of the housing was evaluated by theSTRI method, and a drop from HC1 to HC2 was notobserved after the elapse of more than 3 years.

Photo 1Long-term aging testing of 66-kV termination withcomposite hollow insulator

Table 2Results of withstand voltage tests for terminations

Based on the results of these evaluation tests, it wasdetermined that the 66-kV outdoor termination with composite hollow insulators was fully suited for use in workinglines.

6.

INITIAL APPLICATION TO THE OIHAMALINEThe No. 1 tower of Tokyo Electric Power's Oihama Line islocated in Chuo Ward in the city of Chiba, in an area subject to heavy pollution (ESDD of 0.12 mg/cm2, a Class D
area according to Tokyo Electric Power's system of classification). Cables with a conductor size of 800 mm2 were
led from the tower by outdoor terminations. Normally B1054 porcelain insulators would be used in Class D areas,
but the location on the tower makes washing and other
Table 4

Withstand voltage tests after long-term aging test
Product tested

Test items

Prototype termination for 66 kV(after long-term test)AC

75 kV for 10 min

Good

Lightning impulse-485 kV for 3 times

GoodProduct tested
Prototype for 66 kV
Test items
DC-167 kV for 1 hr

AC

130 kV for 1 hr

Good

Lightning impulse-485 kV for 3 times

GoodTable 3Good

Photo 2Outdoor long-term exposure test set-up

Result of long-term aging tests for terminations
Product tested

Prototype termination for 66 kV

Test items
Test voltage

55 kV

Conditions

Heat cycling
Cable conductor temperature 90°C x 150 cycles
105°C x 30 cycles
Power cycle

8 hr on; 16 hr off

Test period

6 monthResults

Good

Photo 3

Hydrophobicity classification (HC1 to HC2) on insulator surface

55

1535
1285
1185

1443131116710892

φ 308

φ 267

155Figure 1
Table 5

16Termination with composite hollow insulator for very heavy pollution

Composite

Porcelain

Length (mm)

1285

1725

Creepage distance (mm)

4150

4080

Weight (bare) (kg)24145

Estimated weight of termination (kg)Type designation

170

260

CHI-66V1

B-1454maintenance difficult so that B-1454 porcelain insulators,
designed for areas of very heavy pollution (Class E) wereinstalled.
Taking the opportunity offered by re-stringing with 1600mm2 conductors to increase capacity, it was decided touse terminations with composite hollow insulators in aneffort to compensate for the increased load on the arms ofthe tower from the increased mass of the cables.
While the existing terminations using the B-1454 porcelain insulators weighed approximately 260 kg, the use ofterminations with composite hollow insulators (designatedtype CHI-66V1) achieved a weight reduction down toabout 170 kg. The housing of the CHI-66V1 was configured with alternating large and small sheds, achieving an
overall length even shorter than the B-1054 porcelain
insulator for heavy pollution duty, while maintaining acreepage distance equivalent to very heavy pollution duty.
Installation of the 66-kV terminations with composite
hollow insulators was completed in April, 2000 and theywent into commercial service that June.

Photo 4No. 1 tower of 66-kV Oihama Line, bearing outdoor
terminations with composite hollow insulators

tration of moisture to the insulator had no effect on termination performance.
Based on these results, 66-kV terminations with composite hollow insulators were installed in Tokyo ElectricPower's Oihama Line, the first such installation in Japan.
We are currently studying the application of this technology to 154-kV terminations. Terminations with composite
hollow insulators offer the advantages of lighter weightand better anti-pollution performance, and it is hoped thatthey will be applied more widely, to simplify the structureof foundation frame and other ancillary equipment and toreduce maintenance work.

CONCLUSION

Composite hollow insulators have many outstanding qualities, and to render them applicable to outdoor terminations
a series of tests of anti-pollution performance were carriedout on the silicone rubber used as the housing. Guidelines
for application of composite hollow insulators to 66-kV outdoor terminations were also established, and a prototype
was used to confirm electrical performance, both initialand after 6 months aging. It was also confirmed that pene-56

Mounting flange
Lock nut
Conductor fixing metal
Sealing tape
Water-proofing tape
Insulation compoundO-ring
Cable protecting metal
Compressing device
Pre-molded stress-relief cone
Epoxy insulatorUpper cover
Clamping metal
Upper metal
Conductor rod
Composite hollow insulator

Comparison of specifications of 66-kV rated insulators for very heavy pollution
Type of insulator

7.

1216151413121110987654321
No.

REFERENCES
1) Goto et al., Development of 154-kV Joint Termination for Ontower Application, Proc. Energy Division, IEEJ, 1999, 339. (inJapanese)
2) Takeshi Goto et al., "Artificial Contamination Test of Silicone
Rubber Cylindrical Models", Proceedings of The 6th InternationalConference on Properties and Applications of DielectricMaterials, (2000), p.272-275

Furukawa Review, No. 202001

3) Standard of the Japanese Electrotechnical Committee, JEC-34081997 (in Japanese)
4) Federation of Electric Power Companies Japan, ElectricalStandards A-263(1998), In-air Terminations for 66- and 77-kV CVCables. (in Japanese)5) 61462 TR2 IEC:1998
6) Anti-pollution design in substation facilities, ElectricalCooperative Research, Vol.35, No.3, May 1979. (in Japanese)

Manuscript received on November 20, 2000.

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