Installation of the World's First 500-kV XLPE Cable
with Intermediate Joints
by Akira Suzuki *, Shin'ji Nakamura *, Moriaki Matsuda *, Hiroshi Tanaka *2,
Masaaki Shiomitsu *3, Kiyoaki Hiraga *4, Kiyomi Adachi *3, Katsuyoshi Hiratsuka *3,
Kazuhiko Matsuda *2, Masashi Yagi *2, Akihisa Sudo *5 and Kimiji Sugawara *6

Tokyo Electric Power's Kazunogawa Power Station will, when completed, beJapan's largest pumped-storage hydroelectric power station, with an output of 1.6
GW. The first phase is currently under construction, with two 400-MW machines and one cable
circuit. Using leading-edge technology Furukawa Electric has provided 500-kV XLPE cable andassociated extrusion-molded joints (EMJs) and horizontal gas-immersed sealing ends (EBGs) for
the No. 1 and No. 2 machines. Construction was completed in November 1998 and voltage withstand tests have also been performed.
The cable for this line is 2300 m in length, longer than has ever been used in a power stationinterconnect. Because of transportation constraints, insulation-type EMJs are installed at intermediate points. The line is being built under the same basic design concept and installation conditions as the Shin-Keiyo-Toyosu Line now under construction, and reflects the expertise andknowhow acquired there.
The equipment covered here is scheduled to go into service in December, 1999.

ABSTRACT1.

INTRODUCTIONTokyo Electric Power's Kazunogawa Power Station wasplanned for Yamanashi Prefecture to provide the capacity
to satisfy future power requirements, and, when completed, will be Japan's largest pumped-storage hydroelectric
power station. Work is currently under way on the No. 1
and No. 2 machines (together with one cable circuit), andconstruction of the No. 3 and No. 4 machines (with one
cable circuit) is scheduled.
Each of machines No. 1 through No. 4 will have an output of 400 MW for a maximum of 1.6 GW. Output of 400
MW is scheduled to go on line in December, 1999 with afurther 400 MW in July, 2000, followed by the remaining
800 MW at a future date.
Furukawa Electric received an order for the interconnect
for the No. 1 and No. 2 machines, comprising approximately 7000 m of 1 x 1000-mm2 flame-retardant XLPE
cable with reduced insulation thickness, together with six
gas-immersed sealing ends (three of which are horizontal)
and three extrusion-molded joints (EMJs).
Basic and developmental research on the cable andaccessories was begun in 1988, and long-term loading*

Tokyo Electric Power Co., Inc.
*2 Underground Cable Engineering Dept., Power Cables Div.
*3 Power Cable Engineering Dept., Power Cables Div.
*4 Power Cable Manufacturing Dept., Power Cables Div.
*5 2nd Quality Assurance Dept., Power Cables Div.
*6 Underground Cables Dept., Power Cables Div.

cycle verification research targeted at overall verificationof the reliability of technology for the manufacture, shipment inspection and installation of long-span cables,
together with on-site verification tests, have been carriedout, confirming that technology for on-site application is inplace.
Accepting these research results, Tokyo Electric Powermade a decision to apply them to the Shin-Keiyo-Toyosu
Line, which is the world's first long-distance, large-capacity line into a metropolitan center, and construction has
been under way since 1996 with Furukawa Electric's participation.
The experience gained is fully reflected in the equipment for the Kazunogawa power station, with suitable
improvements in installation conditions to match the environment at the site. Furukawa Electric thus approached
the actual installation work after conducting full-scale inhouse tests to confirm performance.
The following describes the cable, accessories, construction methods and so on.

2.

GENERAL DESCRIPTION OF THE
ROUTE

As can be seen from Figure 1, the 2.3-km route--from thehorizontal gas-immersed sealing end (EBG) of the underground power station to the outdoor (vertical) EBG--is covered by a 2.3 km cable, laid entirely within a tunnel in a115

Vertical gas-immersed sealing ends
(EBG) (in switch yard)

Valve panel

Structure

Horizontal snaking pitch: 9.0 m(snake width: 180+18 mm)

Extrusion molded joints(EMJ)
Cable tunnel cross section

Anti-corrosion
protective layer
Horizontal gas-immersed
sealing ends (EBG)(in power station)
Cable tunnel
Pressure tank

Figure 1

Table 1

Cable system schematic and route profile

Structure of cable
Conductor

Code–

CAZV-F

Nominal voltage

kV

500

Conductor screen

No. of cores–

1

Insulation

mm2

1000

Conductor Nominal cross-sectional area

Insulation screen

Miliken type with

Cushion layer

shaped segments

Shielding layer

mm

38.0

Aluminum sheath

Approx. conductor screen thickness

mm

2.0

Anti-corrosion jacket

Minimum insulation thickness

mm

27.0

Nominal outer diameter of insulation

mm

102.0

Approx. insulation screen thickness

mm

1.0

mm

3.0

Aluminum sheath thickness

mm

2.8

Anti-corrosion (PVC) jacket thickness

mm

6.0

Configuration–

Outer diameter

Figure 2

Approx. cushion and shielding layer
thickness

Nominal outer diameter of completed cable

mm

141

Nominal weight per meter

kg m

25.0

Ω/km

0.0187

Dielectric resistivity of insulation at 20°C

MΩ.km

4000

Dielectric resistivity of anti-corrosion

MΩ.km

1

µF/km

0.17

Maximum DC resistance of conductor
at 20°C(flame-retardant) layer at 20°C
Electrostatic capacitancephase-spaced parallel configuration. EMJs are provided atintermediate points. The route has a continuous gradientof 9% and a difference in elevation of 190 m. There is nodanger to the cable from falling objects and a flame-retardant anti-corrosion sheath is used. Thus a snaked methodof installation is adopted, constrained when exposed on
the supporting frames by cleats at points of curvature.
As a measure against problems arising after comple-

116

Cross-section of 500-kV XLPE cable (1 x 1000 mm2
conductor)

tion, the design provides for overage at each joint.
Installation was characterized by severe working conditions, in that there was a continuous gradient of 9%, laying
was carried out in a temporary ventilation, and power outages could be expected during lightning strikes.

3.

THE CABLE

3.1 Cable Structure
The structure of the cable used is shown in Table 1 andFigure 2.
The cable route lay in a mountainous area and transportation access was restricted in both width and height.
Thus the 500-kV XLPE cable normally used for power station interconnects, which has a 32-mm insulation thickness, was found inconvenient to handle, and it was decided to adopt a cable with reduced insulation thickness (27mm specification) 1) that was developed for long-distancelines, was more compact, and had been confirmed tomatch the EMJs.

Furukawa Review, No. 19. 2000

Table 2

Manufacturing quality control procedures for factors
governing performance

Table 3Main performance characteristics of accessories

Characteristic
Factor

QC concerns and preventive measure
Do not allow entry Mesh of extruding machine screen

Impurities Not present

100% inspection of polyethylene resin

Not present

Slice inspection (front and rear ends)

at extrusion

AC withstand voltage
Impulse withstand voltage
Long-term current- carrying
capacity

Air-tightness

3.2 Cable Manufacture and Quality Control
The factor controlling the performance of 500-kV XLPE
cable is impurities, and the countermeasures adopted in
the manufacturing process are set forth in Table 2.
On this cable route, the maximum length of one span
was approximately 1200 m, and using Furukawa Electric's
long-span manufacturing facilities it was possible toachieve 2-span (2400-m) continuous manufacture (extrusion).
Furthermore, at shipment from the factory the cable wassubjected to electrical tests (465 kV AC for 15 min withpartial discharge measurement at a detection sensitivity of
5 pC or more) to confirm quality.
3.3 Grounding Design
As has already been stated, the length of the cable wasapproximately 2300 m, making it impossible to transport it
all at once. Based on the use of a single joint, and on an
estimation of the voltage induced in the sheath and thepartial discharge test to be conducted at the completion of
installation, it was decided to use an EMJ with insulated
flange (insulated joint).
To reduce the voltage induction in the accompanying
communication and other cables, an IV 500-mm2 parallelgrounding wire was installed.

4.

ACCESSORIES

4.1 Accessory Performance
The performance characteristics of the accessories (gasimmersed sealing ends and mid-span joints) used on thisline are shown in Table 3.
4.2 Mid-span Joints (EMJs)
4.2.1 EMJ Design
The mid-span joints represent an extension of the extrusion-molded joint (EMJ) 3) previously developed for 500-kV
XLPE cable.
(1) Designed breakdown stress (EL)• For reinforcing insulation:
AC 27 kV/mm; Imp 60 kV/mm• For treated portion of insulation screen:
AC 27.6 kV/mm; Imp 57.5 kV/mm(2) Harmful level of impurities, voids and protrusions
There is a high probability that the presence of impurities or voids in the insulation or of protrusions from thesemiconducting screen will give rise to tree formations.
Accordingly the permissible dimensions have been calcu-

Internal pressure
Impulse withstand voltage
between shielding layers
Water-tightness

Performance

EMJ

EBG

970 kV for 1 hr
±1960 kV for 3 times
475 kV AC for 30 days
RT-90°C for 25 cycles
RT-105°C for 5 cycles
590 kPa(G) for 30 min(gauge pressure)
440 kPa(G) for 30 min(gauge pressure)––

65 kV for 3 times, at RT,
negative polarity
Water-tightness 98 kPa
for 1 hr–lated and the following limit values determined:• For metallic impurities and protrusions:
100 µm or less
• For fibrous impurities:
2 mm or less
• For voids:
25 µm or less (Note: voids are controlled in the extrusion and curing stages)
4.2.2 EMJ Structure
The structure of the extrusion-molded joint (EMJ) is shownin Figure 3.
4.2.3 Installation Conditions(1) Extrusion conditions
During preheating, the temperature of the conductor
screen, the penciled portion of the cable and the cablesurface is controlled so as to satisfy the conditions for void
suppression. In addition the internal pressure in the moldafter extrusion is controlled to suppress voids.
(2) Curing conditions
The pressure in the curing tube is controlled and thetemperature is regulated in all areas to suppress voids.
4.3 Gas-immersed Sealing Ends (EBGs)
4.3.1 Structure of EBG
In these gas-immersed sealing ends, silicone insulating oil
is used as the main insulation and an oil-impregnatedstress relief cone is used in combination with an epoxy
bell mouth. Figure 4 shows the structure.
In this underground power station the space available
for the cable and machinery is restricted, and this required
development of a new type of EBG to allow direct connection between machinery and the cable, which exits horizontally from the tunnel. This structure is shown in Figure
5.
There are thus two types of EBG structure, dependingon the direction of installation, and for convenience thefirst described is referred to in this paper as "vertical", andthe second as "horizontal".

117

Figure 3

No.

Name

1

Outer sleeve (copper)

2

Ferrule3

Conductor screen

4

Insulation

5

Outer shielding layer

6

Waterproofing compound

7

O-ring

8

Insulator

9

Grounding terminal seat

10

Spacer

11

Epoxy resin + glass tape12

Anti-corrosion layer

13

Gas-collecting port

14

O-ring15

Teflon tube (for inspection)

Cross-section of extrusion-molded joint (EMJ)No.

Figure 4

Cross-section of vertical gas-immersed sealing end (EGB)

Epoxy insulator

2

Conductor rod

3

Upper metal fitting

4

Insulating oil

5Stress-relief cone

6

Bell mouth

7

Lower shield8

Mounting metal9

Oil reservoir

10

Insulator

11

Mounting bolts

12Upper metal shield

13

Gasket14

Base plate

No.

Figure 5

Cross-section of horizontal gas-immersed sealing end (EGB)

4.3.2 Design of the Horizontal EBG(1) Basic structure
The basic structure is an extension of that for the vertical type.
(2) Oil pressure compensation
With the built-in reservoir of the vertical type, there is achance that the friction action of the built-in bellows tankcould be impaired by deflection of the bellows. For thisreason a separately installed cell oil tank was adopted for
greater safety.

118

Name

1

Name

1

Epoxy insulator

2

Conductor rod

3

Upper metal fitting

4

Insulating oil

5Stress-relief cone

6

Bell mouth

7

Lower shield8

Mounting metal

9

Epoxy spacer

10

Insulator

11

Mounting bolts

12Upper metal shield

13

Gasket14

Base plate(3) Measures to prevent cable sag
The length of cable within this sealing end totals about 3
m, and there is comparatively large clearance between
the outer diameter of the inner insulation and the innerdiameter of the epoxy insulator. This raises concerns
about deflection of the inner cable due to the weight of theinner insulation or to thermal expansion, and performancedegradation due to distortion of the inner insulation.
In this sealing end, epoxy spacers are inserted into thisclearance to suppress such deflection. Their effectiveness

Furukawa Review, No. 19. 2000

Photo 1

Transporting the cable drum

Photo 2Laying cable on the groundhas been verified by long-term loading cycle tests (475 kV
for 1 month) conducted at the factory.
(4) Miscellaneous
Because installation is horizontal, the mounting metal isprovided with oil-filling connectors at top and bottom.

5.

CABLE-LAYING WORK

5.1 Transporting the Cable Drum
Because of the large dimensions of the cable drum (flange
diameter of 3.2 m, width of 8.1 m and cable length of 1184m) part of the flanges were removed during overlandtransport from Furukawa Electric's Chiba Plant to the outdoor switch yard of the Kazunogawa power station wherecable-laying was to start (see Photo 1).
5.2 Laying the Cable
Because the cable length was so great and the cable laying site so small, the cable was paid out using a cable
drum shifter and hauling machines.
Limit controller
for cable drum shifter

Photo 3Laying cable in the tunnel

To keep the lateral shift of the drum within the allowable
angle of incidence of the hauling machine and thereby
assure stable pay-out, a roller-type control device wasused with the shifter (see Figure 6 and Photos 2 and 3).

Cable drum shifter
Power supply
500-kgf hauling machines (H/M A and H/M/ B)(SWITCH YARD)
No. 1 distribution panel

Main Control panel S1(cable supply)
Touch roller
Control panel (H/M A)
Control panel (H/M B)(CABLE LEAD)
Speed setting knobs(H/Ms A through C)

350-kgf hauling machines(at 40- 50-m intervals)
Control panel (H/M C)
Main control panel S2 (block)

350-kgf haulingmachine(POWER STATION)

Figure 6

Layout of cable installation system

119Photo 4

Laying cable in the tunnel

5.3 Snaking
A method of snaking was employed because of the continuous 9% cable gradient to prevent the cable sliding
down and to compensate for thermal expansion or contraction. The snaking configuration is shown in Photo 4.

6.

INSTALLATION OF ACCESSORIES

6.1 EBG Installation Techniques
Techniques for adapting to 500-kV service and for the
installation of the horizontal gas-immersed sealing ends
(EBGs) are as described below.
6.1.1 500-kV Adaptation
Furukawa Electric installed the vertical EBGs in the outdoor switch yard and the horizontal EBGs in the underground power station. The use of horizontal EBGs wasparticularly effective underground in reducing the spacerequired for installation and the cost of the work.
The working environment was particularly unfavorable
in that the vertical (outdoor) EBGs had to be installed during the monsoon rains, and there was considerable dust
generated by other construction during installation of thehorizontal (underground) EBGs. Thus a "work room,"which prevented the adherence of moisture and impurities, was built for the installation work.
6.1.2 Horizontal EBGs
Installation of the horizontal gas-immersed sealing ends
was attended by three main problems: 1) inserting the350-kg insulator tube into the cable; 2) preventing theentry of impurities during insertion; and 3) sagging of thecable under its own weight during insertion of the insulator
tube.
New equipment and methods were developed andadopted to overcome these problems. The specifics (seePhoto 5) are described below.
(1) Adjusting dolly: An adjusting dolly was developed toallow fine adjustments (up-down, left-right and rotational)
during insertion of the insulator tube. This also prevented
the settling and adherence of impurities.
(2) Use of a holding device for the conductor: A holding

120

Photo 5

Techniques for laying the horizontal gas-immersed
sealing end

device is attached to the conductor rod when the joint ismade, preventing cable sag.
(3) Use of an assembly guide rod: An insertion guiderod is pre-attached, and the insulator tube is inserted
along it.
6.2 EMJ Installation Techniques
Extrusion-molded joints have already been developed for
500-kV lines and are being installed for commercial service. Prior to installing the EMJs for the present project,
we reconfirmed the installation conditions imposed by thedifference in conductor size, checked installation procedures by creating a factory model of the work site, andconfirmed electrical performance. The actual line wasassembled based on these confirmations.
6.2.1 500-kV Adaptation
Cleanroom specifications were tightened over those usedfor 275 kV, for stricter control of impurities. A high-performance inspection system designed to eliminate impurities(see Photos 6 and 7) was also developed and applied.
(1) Development of a 100% inspection system for impurities in the polyethylene resin: A system was developedthat inspects the resin being extruded for impurities bylaser scanning. It was thus possible to confirm that there
were no harmful impurities whatever introduced during
extrusion.
(2) Development of an IP photographic inspection system: Joints are X-rayed after extrusion and curing to confirm that there are no harmful impurities present. In the
new system, an imaging plate (IP) is used instead of film,
providing a more sensitive and more accurate image, andimproving the repeatability and efficiency of the inspection.
6.2.2 Adaptation to the Kazunogawa Power Station
The tunnel in which the cable is installed is also used as atemporary ventilation duct for the underground power station, creating air drafts with a velocity of 3-4 m/s. The tun-

Furukawa Review, No. 19. 2000

Photo 6

System for 100% inspection for impurities in thepolyethylene resinnel also slopes at 9%, and a stable installation environment has to be maintained in it. Since assembly was carried out during the summer season, provision had to bemade for power outages caused by lightning andtyphoons.
(1) Measures to prevent drafts: PVC slate outer wall
was erected, and a cleanroom was built inside for thejointing work.
(2) Measures against slope: A scaffolding was erected
to provide a level area in which to work, thereby negating
the effect of the 9% slope.
(3) Measures in the event of power outage: An electricalgenerator was installed that would start automatically inthe event of power outages.

7.

Photo 7

System for photographic inspection using imaging
plateswhile bi-directional communication made it possible tochange the phase being measured and insert simulated
pulses.
7.3 Test Results
Measurements carried out on the 500-kV XLPE cable for
Kazunogawa No.1 produced satisfactory results on boththe first and second passes. Table 4 shows the respective
measurement frequencies and detection sensitivities.

TESTING

7.1 Test Conditions
Partial discharge measurement tests using high-frequency
tuning were conducted on two occasions. The first, during
the dielectric strength test, involved application of 1.1 E for
10 min to each phase in turn; the second, during the preliminary charging test, involved a 3-phase (batched) testwith preliminary charging voltage for 3.5 hrs.
7.2 Measuring Circuit
Local stations were set up near the measurement points(for outdoor EBG, EMJ and power station EBG measurement), and the measurement signal was converted into an
optical signal for batched monitoring at the master stationin the pit at the Kazunogawa power station (see Figure 7).
The circuit that was adopted provided for optical relaying of all frequencies from 1 to 50 MHz from foil electrodes
mounted on the surface of each insulated joint to the master station. This allowed identification of noise, changing of
measurement frequency, etc. to be accomplished easily,

8.

CONCLUSION

The on-site installation of 500-kV XLPE cable for the
Kazunogawa power station was completed without misadventure or accident in November, 1998.
From basic research of 500-kV XLPE cable to its commercialization took approximately 10 years, and commercial operation is scheduled to commence in December,1999. It is anticipated that the results obtained will be fullyreflected in the Shin-Keiyo-Toyosu line, the laying of
which is currently in progress, and that further use of
these techniques will be made in underground trunk lines
to be installed in the future.
In closing the authors would like to express their deep
appreciation to persons involved at both Tokyo ElectricPower Co.,Inc. and Furukawa Electric.

121

Switch yard

DETPower station

EMJ
PRB

1150m

PRB

1150m

DET

DET
SWG

SWG

SWG

PG

BPF

BPF
BEF

SWG

SWG

CTRL

AMP

E/O

SWG

BPF

PG

PG

BEF

BEF

AMP

CTRL

AMP

CTRL

E/O

E/O

MH-UNIT
1-50-MHz signal
Control signal (Phase switching, PG output, etc.)
High-frequency signal
Low-frequency signal

Ch-8

OSC

Server

OSC

PC

Ch-7

Ch-3

Ch-2

Ch-1

E/O

E/O

E/O

E/O

E/O

E/O

φ-q-t display

ANLY

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

PC

CHSW

A/D

PC

Input unit
TAMP

TAMP

TAMP

TAMP

TAMP

TAMP

TAMP

TAMP

PJDG

PJDG

PJDG

PJDG

PJDG

PJDG

PJDG

PJDG

MCTL
Peak Hold

ALM

Master station

Block diagram of system for measurement of partial discharge

Measurement frequencies and detection sensitivities
in partial discharge tests

1st pass

Outdoor gas-immersed sealing end

Phase

Black

Red

White

Measurement frequency

20.0

21.0

21.5

Detection sensitivity

1.8

1.8

1.6

Extrusion-molded joint

Phase

Black

Red

White

Measurement frequency

23.1

23.2

23.1

Detection sensitivity

1.9

2.1

2.6

REFERENCES

1) Tanaka et al.: Technology Advances in XLPE Cables: Part 3 -Development of Long-line 500-kV XLPE Cables and Joints, No
97, Furukawa Electric Review, 1995. (in Japanese)
2) Kaminaga et al.: Development of 500-kV XLPE Cables, March
1995, Transactions of IEEJ, Part B, 1995. (in Japanese)
3) Kaminaga et al.: Development of EMJs for 500-kV XLPE
Cables, March 1995, Transactions of IEEJ, Part B, 1995. (inJapanese)
Manuscript received on June 28, 1999.

Power station gas-immersed sealing end

Phase

Black

Red

White

Measurement frequency

21.2

23.2

21.2

Detection sensitivity

1.0

0.9

0.9

2nd pass
Phase

Ch-4

E/O

Figure 7

1st pass

Ch-5

E/O

During φ-q confirmation,
to tuned amplifier output

1st pass

Ch-6

Optical fiber (bi-directional transmission)

CTRL

During locating,LAN
to channel switching output

Table 4

A/D:
A/D converter
ALM: Alarm unit
ANLY: Spectrum analyzer
CHSW: Channel switch
CTRL: Control equipment
DET: Detector
MCTL: Measurement control
OSC: Oscilloscope
PC:
Personal computer
PJDG: Primary judging equipment
PRB: Probe
SWG: Switchgear
TAMP: Tuned amplifierPRB

3 phases (batched)
Switch yard

EMJ

Power station

Measurement frequency

21.5

23.1

24.4

Detection sensitivity

6.5

4.3

2.4

Unit ofMeasurement frequency: MHz
Detection sensitivity: pC

122

Furukawa Review, No. 19. 2000