Supply of Dry Type Terminations for 275-kV XLPE Cables
by Kiyomi Adachi *, Yasuo Torai *, Shunsuke Abe *2 and Shin-ichi Fukano *3

Conventionally, an oil-immersed type termination has been generally used for
275-kV XLPE cables, but because of the use of oil, thoroughgoing review has
been requested from viewpoints of maintenance problems and installation. As the research oncomposite prefabricated insulation advances, actual applications at super-high voltage haveincreased, and the reliability has been improved, a completely dry type termination free of insulation oil has been developed and applied to the actual lines of Tokyo Electric Power Company.
With this technique applied, an inverted termination that can reduce the size of substation facilities was developed, and was applied to the actual lines of the Kansai Electric Power Company. In
this line, a semiconductive-layer shaver of lightweight and high-performance was developed
achieving --ahead of other companies--smooth and high-performance cable treatment in the vertical direction.

ABSTRACT1.

INTRODUCTION

For direct-coupling type termination for XLPE cables, aso-called dry type using a compound prefabricated insulation structure is generally applied for 66-154 kV XLPE
cables and a so-called oil-immersed type insulation system using silicone insulation oil is popularly applied for the
275-kV XLPE cables.
The oil-immersed type termination must have an oilpressure compensator equipped as ancillary facilities
because insulation oil is used, and requests for developing a dry type termination have been increased from viewpoints of both maintenance and installation. On the other
hand, in the laboratory, development of a straight-line termination (PJ) in a prefabricated insulation structure using
the epoxy unit and rubber pre-molded insulator for XLPE
cables has been advanced for the application to 500 kV,
and in the actual line, the technique has been able to be
applied to the voltage as high as 275 kV, and the reliability
has been remarkably improved. With these as backgrounds, the authors began development of a completely
dry type termination using this technique, and have supplied terminations for SF6 gas (EB-G) and terminations foroil (EB-O) for application to actual lines.
In these actual lines, a "semiconductive-layer shaver"
was applied for achieving the stabilized installation quality
and shortening the working time for the Kansai ElectricPower Company, and various kinds of terminations suchas inverted termination that can downsize the cable layoutof underground substation facilities were developed and*Power Cables Engineering Dept., Power Cables Div.
Underground Cables Engineering Dept., Power Cables Div.
*3 Quality Assurance Dept., Power Cable Accessories Div.
*2

supplied to meet diversified customers' needs. The "semiconductive-layer shaver" which enables vertical shaping
for the termination provides satisfactory shaping performance irrespective of the normal or the inverted, and ourcase was the Japan's first application in super-high voltage.
For the main insulation parts comprising the termination,
the quality was verified at the plant in conformity to theacceptance test set forth in JEC 3408-1997 1) newly instituted.
This paper introduces the design, performance verification, and supply of the equipment-directly-coupled termination.

2.

DEVELOPMENT

2.1 Target Specifications
2.1.1 Profile and Dimensions
The profile, structure, and dimensions were determinedwith compatibility with conventional oil-immersed type termination taken into account as well as in conformity to thedimensional standard for interconnection with equipment.
(1) Termination for Gas
Figure 1 shows the structure of termination for gas.
(2) Termination for Oil
Figure 2 shows the structure of termination for oil.
The total length is the same as for prefabricated units
thereby achieving compactness.
2.1.2 Electrical Performance
The objective performance was set as shown in Table 1 inconformity to the 275-kV XLPE cables as well as to theprefabricated type straight-line termination (PJ).

972.1.3 Mechanical Performance
The mechanical performance was set as shown in Table 2
with short-circuit electromagnetic force, seismic force, andspring force taken into account. The applicable standard isJEC 3408-1997 1).

2.2.2 Insulation Design
Based on the previously demonstrated capability and performance, insulation was designed. The electric field
analysis results are shown in Table 3 and equi-potential
lines of electric field are shown in Figures 3 and 4.
The results shown in Table 3 indicate that all values arelower than the previously demonstrated working stresses
and the insulation is free of any problem.

2.2 Design
2.2.1 Design Elements
The insulation structure of the termination must achieve
the objective performance under the restrictions of theinterconnection geometry. The epoxy insulator specified
for interconnection was equivalent to or greater than theoutside diameter of 275-kV PJ unit, thus the insulation
structure of the unit was adopted. Consequently, it was
assumed satisfactory as long as insulation harmony withthe facilities and mechanical performance represented bybending stress generated by earthquakes, etc. are
obtained by the termination structure.

1

13

2

3

5

4

7

6 14

2.2.3 Mechanical Design
For mechanical properties of the termination, based on
the conditions shown in Table 2, the bending stress generated in the epoxy insulator base was computed, and it
was confirmed that the termination satisfied allowable values. It was also confirmed experimentally that the actual
epoxy insulator possessed the objective bending withstand load.

15
14
13
12

8

9

11

12

15
10

Gasket for base plate *Equipment bottom plate *Shield *Water-proof tape layer
Compression device for11
stress-relief cone
10 Cable protection tube
9 Insulating flange
8 Adapter
7 Fixing bolt
6 Fitting
5 FRP pipe
4 Lower shield
3 Stress-relief cone
2 Epoxy insulator
1 Conductor rod
No. Parts name* To be supplied by transformer
manufacturer

Figure 1

Nominal cross sectional Dimensions (mm)area of conductor
D(mm2)
800~2000
44
2500
60

Structure of EB-G

15

Water-proof tape layer
Compression device forstress-relief cone
13 Cable protection tube
12 Epoxy insulator
11 Adapter
10 Packing for base plate *9 Base plate *8 Fixing bolt
7 Fitting
6 FRP pipe
5 Lower shield
4 Stress-relief cone
3 Epoxy insulator
2 Conductor rod
1 Shield ring
No. Parts name
14

6
1

2

3

4

8

5

7

9

10
11

12

15

14
13

* To be supplied by transformer
manufacturer

Figure 298

Structure of EB-O

Nominal cross sectional Dimensions (mm)area of conductor
A
L
d
(mm2)
1000 or less
85 1085 45
1000~2000
110 1110 60

Furukawa Review, No. 19. 2000

3.

did not breakdown at 910-960 kV for power frequency
voltage and at 2195 kV for lightning impulse voltage withrespect to the objective electrical properties shown in
Table 1, and satisfactory initial properties of as much as
1.4-1.5 times the specified values were obtained. Table 4shows the results.

ACTUAL DEVICE EVALUATION

3.1 Electrical Performance
Results of electrical tests using actual devices were satisfactory, and both initial and long-term performance sufficiently satisfied the objective performance.
3.1.1 Initial Performance
It was confirmed that the initial performance satisfied theobjective performance. In addition, marginal performance
was grasped by breakdown tests, in which the termination
Table 1

Tank (φ 640 mm)
SF6 gasInner electrode(ground side)UppershieldObjective electrical performance

Cable (t=23 mm)

Performance

Item±1445 kV/ 3 cycles 1)

Lighting impulse withstand voltage

Stress-relief
cone

Epoxy insulator
Inner electrode (high-voltage side)

Figure 3

Equi-potential line of electric field of dry type gas
immersed termination

Figure 4

Equi-potential line of electric field of dry type oil
immersed termination-1590 kV/ 3 cycles 2)

Power-frequency long-term

525 kV/ 1 hr 1)

withstand voltage

610 kV/ 12 hr 2)

Lightning impulse withstand voltage-55 kV/ 3 cycles 1)of insulation between shielded layers-50 kV/ 3 cycles 2)
1 st: 220 kV/ 5 pC or lower

Power-frequency partial discharge 1)

2 nd: 310 kV/ 30 pC or lower
3 rd: 220 kV/ 5 pC or lower

Note 1: Objective electrical properties of Electric Power Company A
Note 2: Objective electrical properties of Electric Power Company B

Table 2

Objective mechanical performance of epoxy insulator
Performance

Item

10°C/ 60 min ←→ 100°C/ 60 min 1)
0°C/ 60 min ←→100°C/ 60 min 2)

Heat shock

Table 410 cycles
300 kV/ 10 min 1)

Power frequency partial
discharge

No.

11.8 (kN)

Note 1: Objective electrical performance of Electric Power Company A
Note 2: Objective electrical performance of Electric Power Company B

Breakdown voltage

2

EB-G

910 kV/ 8 min

Test terminal

2500

3

EB-O

-2195 kV/ 3 times

Not broken

2000

960 kV/ 8 min

Evaluated portion

PortionDry type
PJ
EB-G EB-O
Epoxy insulator
High-voltage end of embedded electrode
Epoxy insulator
Grounding end of embedded electrode

G3

Epoxy/rubber interface 2500

EB-G

Imp

Dry type

G2

(mm2)

Working stress on major elements

AC

G1

Place of breakdown

1

Working stress on elements
Mark

Size

Type

Detection sensitivity: 5 pC or lower

Table 3

Test results

Sample220 kV/ 10 min 2)

Bending withstand loading

Breakdown voltage of dry type termination

EB-G: gas interface
EB-O: insulation oil interface

2.6

3.0

PJ
EB-G EB-O

5.9

16.9

20.1

39.2
G3

2.2

2.1

-

14.9

13.7

-

0.9

0.7

-

6.1

4.6

-

8.1

7.0

9.5

G4

Epoxy/rubber interface

1.2

1.1

1.4

G5

XLPE/rubber interface

1.0

0.9

0.9

6.6

6.0

5.7

G6

Building-up (XLPE)

5.4

5.4

5.4

35.5

35.5

35.5

_
[Evaluation voltage] AC: 275/√ 3, Imp: 1050 kV

G1

G2

G4
G5
XLPE
Conductor

G6

Cable: 275 kV 1x2500 mm2 (t=23)99

3.1.2 Long-term Performance
In developing the present termination, it was confirmedthat a deterioration index n=15 was able to be adopted forthe design value based on basic examinations, etc. of PJ
developed in the similar period, but in verifying the longterm performance, evaluation at deterioration index n=9
which had been adopted until then was carried out in addition to the evaluation at deterioration index n=15.
(1) Long-term loading cycle test (No. 1)
In order to confirm that the termination satisfies thelong-term performance requirements, in-plant longterm loading cycle tests were carried out. The termination withstood the tests equivalent to 30-year service life at deterioration index n=9 by voltage acceleration, and proved that it possessed satisfactory properties.
(2) Long-term loading cycle test (No. 2)
In the Yokosuka Laboratory of Central ResearchInstitute of Electric Power Industry, the termination
was used as a terminal of PJ developed in the similar
period for long-term loading cycle tests, and the termination withstood the tests equivalent to 30-year service life at deterioration index n=15 by voltage acceleration, thereby proving that it possessed satisfactory
properties.

Table 5

Test conditions of in-plant long-term loading cycle
tests
Item

Characteristic value

Cable specifications

2500 mm2

t=23

EB-G

Termination class
Voltage

320 kV

Equivalent to 30

Period30 dayyears, with n=9

Loading
Current

Tempera-loadingheat cycle
and result

Remarks

ture andperiodTables 5 and 6 show test conditions and results of thetests described in Paragraphs (1) and (2).
3.2 Mechanical Properties
Using epoxy insulator comprising the termination,mechanical properties were verified.
In heat shock tests and the subsequent partial discharge tests, satisfactory mechanical properties were verified. In addition, in the tensile and bending withstand load
test after heat shock tests, favorable results that satisfied
specified values were also verified. Bending tests werecarried out to failure, and the termination did not break at
19.6 kN for the specified values, indicating that it provided
satisfactory mechanical properties.

4.

TYPE TEST

4.1 Structures of EB-G and EB-O
In applying the termination to the actual 275-kV local link
line, type tests were carried out on EB-G (including inverted type) and EB-O by sample assembly in the structures
shown in Figures 1 and 2. The inverted type is of thesame structure as the normal type, but a new engineering
method specific for the inverted type was developed andapplied for installation and maintenance.
4.2 Type Test Conditions
Typical type test conditions and the results of EB-G and
EB-O are shown in Tables 7 and 8 for type A (EB-G, EBO) and for type B (normal and inverted EB-G), respectively, because test conditions are different.
For all types, satisfactory results were obtained in all thetest items.

RT~90°C
1 cycle/day x 25 days

Good

RT~105°C
1 cycle/day x 5 days

Table 7
Table 6

Results of long-term loading cycle tests

Item
Cable specifications

Characteristic value
2500 mm2 t=23

Termination class

EB-G

Loading

245 kVconditions

Voltage
PeriodRemarks

resultCurrentloadingheat cycle
and result

100

VoltageTime* Loading efficiency

years, with n=15

Temperature andperiod3474.5 hr

RT~105°C
1 cycle/day x 12 days

525 kV, 1 hr(room temperature)±1445 kV, 3 times eachLightning impulse withstand(room temperature)

voltage test
Lightning impulse withstand voltage

Equivalent to 31.6
years, with n=15

RT~90°C
1 cycle/day x 132 days

5 pC or lower

test of insulation between shielded
layers 1)Good*-55 kV, 3 times(room temperature)
588 kPa/ G, 30 min

Air-tightness testGood

(room temperature)

withstand voltage test

6 months

Results

300 kV, 10 min

Power-frequency withstandPower-frequency long-term
Equivalent to 30

245 kV

Test conditions

Test item

voltage partial discharge test

80% taken into accountLoading

Test conditions and results (Type A)

Good

Good

Good

Good

Cable specifications: 2500 mm2 t=23 (EB-G)
1400 mm2 t=23 (EB-O)

1) Executed on EB-G only

Furukawa Review, No. 19. 2000

Table 8

Test conditions and results (Type B)
Results

Test conditions

Test item±925 kV, 3 times each

Switching impulse withstand voltage testGood

(room temperature)-500 kV, 1 hr

DC withstand voltage testGood

(room temperature)
1 st: 220 kV/ 1 min; 5 pC or lower
2 nd: 310 kV/ 1 min; 30 pC or lower

Partial discharge testGood

3 rd: 220 kV/ 1 min; 5 pC or lower
610 kV, 12 hr

Power-frequency long-term withstandGood(room temperature)

voltage test
Breakdown test for the above

50 kV for 1 hr

Broken at 1160 kV

to failure by voltage step-ups

for 5 minLightning impulse withstand voltage test for-50 kV, 3 times each

insulation between termination metal sheaths(room temperature)

Breakdown test for the above

Good

Voltage increased three times by-90 kV, Broken at the-5 kV steps up to failure

first application±1590 kV, 3 times eachLightning impulse withstand voltage testGood

(room temperature)

Breakdown test for the above

Voltage increased three times by-2540 kV, Broken at-5 kV steps up to failure

the first application

1080 kPa/ G, 30 min

Good

Pressure proof test and air-tightness test
* Cable specifications: 2000 mm2 t=23

Table 9Line name

Cable size

Type

Chiba Central Substation

800 mm2 CAZVNormal EB-G

Tokyo Electric Power

Chiba Central Substation

800 mm2 CAZVNormal EB-G

Kansai Electric Power

Sannomiya Substation

1000 mm2 CAZVNormal EB-G

Applied6 phases

Kansai Electric Power

Sannomiya Substation

1000 mm2 CAZVInverted EB-G

Applied6 phases

Kansai Electric Power

Sannomiya Line

2000 mm2 CSZVNormal EB-G

Applied6 phasesCustomerTokyo Electric Power

5.

ACCEPTANCE TEST

For the acceptance test at the time of shipment from theplant, 100% heat shock and partial discharge tests were
performed on epoxy products, 100% radiographic inspection and partial discharge tests on stress-relief cones, and100% spring force characteristic tests on the compression
device under the conditions of as discrete component andas assembled, thus confirming the quality of each component.

6.

Supply records
Semiconductive layer shaver

Quantity
6 phases
6 phases

In applying the semiconductive-layer shaver to EB-G
and EB-O, since cables must be longitudinally arranged
as against the case of PJ --for which cables are arranged
horizontally, a lightweight and high-performance semiconductive-layer shaver which can move not only horizontally
but also vertically was developed. By applying thismachine, the cable insulator surface obtained satisfactorysmoothness before mirror finish.
In the finish by glass shaving in which no semiconductive-layer shaver is used, providing mirror-finish after
paper-finish secured satisfactory performance.

INSTALLATION METHOD

The installation methods are based on the conventional
PJ engineering method. Of these, the semiconductivelayer shaving method falls into two general broad categories: "glass shaving + paper finish + mirror finish" and"semiconductive-layer shaver + mirror finish". In the lines
to which the termination was supplied this time, both ofthese two engineering methods were adopted.

7.

SUPPLY RECORDS

Table 9 shows the supply records of 275-kV dry-type termination for 275-kV XLPE cables.

101

8.

SUMMARY

Based on the techniques applied to actual lines, after
developing 275-kV PJ, a dry-type termination, which canreplace the conventional oil-immersion type, was developed and supplied to actual lines. The inverted type
recently developed in addition to the normal type will contribute to downsizing of substation facilities and increased
applications are expected.
Finally, the authors thank the personnel of Tokyo
Electric Power Company and the Kansai Electric Power
Company, for their advice and cooperation in constructing
the line.

REFERENCES

1) JEC 3408-1997; High Voltage Tests on Cross-linked
Polyethylene Insulted Cables and their Accessories for Rated
Voltages from 11 kV up to 275 kV.
2) Shirai et al.; Study on the installation of dry-type EB-G for 500kV CV cables, Proc. of Energy Group of IEEJ, No.336, August
1999. (in Japanese)
Manuscript received on November 11, 1999.

102

Furukawa Review, No. 19. 2000