Furukawa Electric, VISCAS, Inoue Manufacturing, Asahi Electric Works,
Furukawa Electric Industrial Cable

Underground Power Cable, Distribution Cable, Overhead
Transmission Line, Industrial Cable and Their Accessories
by Shinji Umeda *1, Noboru Ishii *1, Noriaki Horiguchi *1, Makoto Maeda *1, Takumi Yamaguchi *2,
Hideo Tanaka *3, Hiroshi Niinobe *3, Takehiko Mizuno *3, Satoru Maruyama *3, Kunio Iwasaki *4,
Hiroyuki Majima *5, Shigekazu Amanuma *6, Hideki Kamiyama *7, Masaji Tokita *8, Shingo Oya *9,
Hiromichi Shigeta *10 and Hiroji Akasaka *10

In the area of electric energy, recent years have seen expanding deregulation ofelectric utilities, heightened consciousness about secured supply, the global
warming problem and the like, which lead to significant changes in the environment surrounding
the electric power industries. Thus, Furukawa Electric has been promoting technological developments on the premise that safety and security is the first priority, concentrating on preservation of the global environment and supply of new products that are lean, compact and economical. In this report, technological achievements of the Furukawa Electric Group comprising
Furukawa Electric, VISCAS, Inoue Manufacturing, Asahi Electric Works and Furukawa ElectricIndustrial Cable are presented on a categorized basis.

ABSTRACTEXTRA-HIGH VOLTAGE POWER
CABLES

Extra-high voltage cables over 66-kV rating may be categorized into OF (Oil Filled), POF (Pipe Oil Filled) and CV(Cross-Linked Polyethylene Insulated PVC Sheathed, i.e.,
XLPE) cables, and we took the worldwide initiative in developing these cables of 500-kV rating which corresponds tothe world’s highest voltage. Among these, XLPE cable has
made a remarkable progress since its first application 50
years ago, with respect to the material, structure, manufacturing technology and quality control technology. As illustrated in Figure 1, the cable has been downsized by meansof insulation thickness reduction (i.e., increase in electricalstress), thereby putting 500-kV long-length XLPE cableand large- sized, long- length CVT (Cross- Linked
Polyethylene Insulated PVC Sheathed Triplex, i.e., Triplextype XLPE) cable into practical application.

*1 Power Cable Engineering Dept., VISCAS*2 Installation Engineering Dept., VISCAS*3 R&D Dept., Technological Administration Div., VISCAS*4 Distribution Cable Dept., VISCAS*5 Power Equipment Dept., Inoue Manufacturing*6 O v e r h e a d P o w e r Tr a n s m i s s i o n L i n e R e s e a r c h &Development Dept., Technological Administration Div.,VISCAS*7 Overhead Power Transmission Engineering Dep., Power
Transmission Div., VISCAS*8 Engineering Dept., Asahi Electric Works*9 Engineering Dept., Furukawa Electric Industrial Cable*10 Engineering Dept., Energy Div., Energy & Industrial Products
Co., Furukawa Electric

1.1 500-kV XLPE Cable
500-kV XLPE cables have been adopted in long-distanceunderground power transmission lines such as for Tokyo
Electric Power Company’s Shin-Keiyo-Toyosu Line(approx. 39.8 km x 2 circuit, total number of intermediate

Voltage

History of the insulation thickness

500 kV35→32→27 mm

275 kV

27→23 mm

220 kV

23→20 mm

154 kV23→19→17 mm

77 kV

17→15→13→11 mm

66 kV

15→13→11→ 9 mm

14.0

Average electrical stress (kV/mm)

1.

500kV

12.0
10.0

220kV

8.0

275kV

6.0
154kV

4.0
66kV

2.0
0
1965

77kV

1970

1975

1980

1985

1990

1995

2000

Year

Figure 1

Trends in voltage upgrading and electrical stressincrease.

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joint: 240 phase, maximum span: 1,800 m), as well as inoutgoing lines from power plants. Figure 2 shows a sceneof cable installation for the Kan’nagawa Hydraulic Power
Plant of Tokyo Electric Power Company in 2003. Because
the cable was so long in unit length as to reach 1,800 m,
ordinary methods were unable to deal with its transportation. Accordingly, the cable was transported from the
manufacturing plant to Hitachi Port by sea, and from
where to the power plant by land using a special-purpose
vehicle under a restriction of nighttime-only traveling,
spending an unprecedentedly long transportation time ofseven days.
With respect to connection with the power equipment,
an inverted type of gas-immersed termination joint wasneeded, so that we developed a new joint after reviewing
its inner structure, having succeeded in delivery ahead ofother manufacturers.
We have accumulated several track records of 500-kV
XLPE cables domestically since then, and having gained
a foothold in overseas market through our recent delivery
to China, we plant to receive more orders from overseas.
1.2 Cable Downsizing and Capacity Increase
We have developed jointly with Tokyo Electric Power
Company the Triplex-type XLPE cable having a sectored
cross-section shown in Figure 3, and have applied thecable to many practical transmission lines since 1998. It
was intended that the new cable design would be applied
to increase the transmission capacity (i.e., increasing the

Figure 2

Installation of a long-length cable using a specialpurpose vehicle.

Figure 3

Appearance of sectored Triplex-type XLPE cable.

conductor size) while making efficient use of existing
cable conduits, because the costs related with civil engineering work to construct new cable conduits were very
expensive. This development has made it possible toapply 500-mm2 sized cables to those transmission lines
where the maximum cable size was limited to 325 mm2
due to the duct size restriction, thereby achieving acapacity increase.
1.3 Large-Sized Triplex-type XLPE Cable
Although the largest conductor size of Triplex-type XLPE
cables was conventionally limited to 600 mm 2 due tomanufacturing difficulties, we have overcome these problems and subsequently investigated the characteristic
thermal behavior of large-sized segmented conductor
cables at the time of stranding. As a result, taking into
account these results in installation design, we were able
to expand the size of 66-kV and 154-kV Triplex-type
XLPE cables up to 1,000 mm2. The specification based onthese results has been adopted since 2005 as a standard
for practical lines, resulting in a number of improvements
such as reducing the space for cable accommodation,
efficiency increase in cable laying (i.e., enabling laying of
three phases in a shorter period of time), reducing the line
construction costs and downsizing of manholes due toelimination of cable offset.
1.4 DC XLPE Cable
There is much need for DC transmission cables for its
higher power transmission efficiency with no AC losses.
Until recently, AC power transmission was preferred to DC
transmission due to the fact that AC-DC power converters
to be installed at either end of the cable line are expensive
thus causing an increase in total construction cost. As thecost of power converter decreases, however, applicationof DC power transmission is expected to expand.
But, in developing DC XLPE cables, it was found that
the AC insulation material (i.e., cross-linked polyethylene)
was not directly applicable to DC cables due to the problem of space charge accumulation within the insulationmaterial. Accordingly, we have developed a DC insulationmaterial which can control space charge accumulation,and have confirmed that the prototyped DC 250-kV and
500-kV XLPE cables are provided with superior electricalproperties including long-term characteristics.

Figure 4

Large-sized Triplex-type XLPE cable and its installation.

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Moreover, taking advantage of the DC cable technology
mentioned above, we have recently embarked on thedevelopment of coaxially-integrated return conductor DC
XLPE cables (i.e., DC coaxial cables), in which the main
DC cable and the return cable are integrated into a single
cable, and the development has advanced to the stage ofthe 250-kV class.
1.5 Submarine Cable
There are firm demands for submarine cables both athome and abroad.
In 2004, we have delivered to the Matsushima-Narao
Line of Kyusyu Electric Power Company connecting the
Matsushima Substation on the Kyushu mainland side andthe Narao Substation on the Goto side a large volume of
66-kV optical fiber-composite submarine power cable inlump-sum, totaling approximately 2,670 ton in mass and
54 km in length, which equals the world-class length asan AC triplex XLPE submarine cable. The Line comprised
two cable lines, and the cable laying work was carriedout, under the direction of Kyusyu Electric Power
Company, by a joint venture consisted of four companies
headed by Furukawa Electric.
Although the cable structure had a proven track record,
the unexperienced length of the cable made it indispensable to factory joint the power cable and the optical fiber
unit. Accordingly, in addition to the conventional inspection items specified in the CIGRE recommendations, wehave reviewed the history of procedures that the cable isanticipated to undergo ranging from manufacturing at theplant to final installation at the site, and, after designing
the cable taking these results into consideration, we confirmed the validity of the design by verification.
In this cable laying work done by the four-company
joint venture, a cable laying ship built by using puredomestic technologies and provided with the dynamic
positioning system (DPS) “Tenzan” played an active role(see Figure 8). The ship traveled, in a complete DPS
scheme without using anchor at all, the whole 54-km
route to lay and bury the cable at a pace of one line in tendays (day and night).
High-accuracy cable laying with an accuracy of not

Figure 5 500-kV DC XLPE
Figure 6 ±250-kV DC coaxial		cable.		
submarine power cable.

more than ±5 m for straight sections and not more than
±10 m for curved sections has been achieved. The cableburial depth was set at 1.5 m to avoid damages due toanchoring. In terms of burial method, the simultaneous
laying and burying method was applied where a cablepaid out from a laying ship is immediately buried by aburying machine that is tugged by the laying ship (seeFigure 9).
It is expected that, as a result of this achievement,

Figure 7

Figure 8

Figure 9

Appearance of typical submarine cable.

Cable laying ship “Tenzan” with DPS function, built
by using pure domestic technologies.

Conceptual image of simultaneous laying and burying using a cable laying ship with DPS function.

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demand for isolated island connection cables over long
distances will grow in future.

2.

JOINT FOR HIGH-VOLTAGE XLPECABLES

Because XLPE cable is characterized by its ease of maintenance, the cable rapidly proliferated domestically in the
1960s when its application began, currently constituting
the majority of domestic power cables having voltage ratings of 66-kV and higher. During this period, we havedeveloped the sealing end and the extrusion molded joint
for XLPE cable joints, achieving significant improvements
in terms of performance, ease of installation, reduction of
joint size and so forth.
As the cable rating was upgraded from the 66-kV classto the 154-kV, 275-kV and further to the 500-kV class, we
carried out development concentrating on the reliability
and work management of joints, thereby achieving an
extremely low rate of dielectric breakdown across theworld. Moreover, since the late 1990s when 500-kV XLPE
cables have been put into actual use, studies have been
made focusing on simplifying the installation process forjoints as well as reducing their sizes, and new joints thatutilize new structures and materials have been developed
for practical application.
A rubber block-based intermediate joint named cold
shrinkable joint (CSJ) is one of these developments,
which is aimed at simplifying the installation process. The
structure of CSJ is such that a rubber block insulator (seeFigure 10) that is molded at the factory in advance is used
as a reinforcing insulator to fit to the cable joint. The CSJ
has achieved, due to its simple structure, a significant
reduction in installation time and simplification of work
management when compared with taped joints where an
insulating tape is wound at the work site, or with field
molded joints where cross-linked polyethylene is used tointegrally mold the cable at high pressure and high temperature. Currently the CSJ is practically applied to the
154-kV class domestically as well as to the 220-kV classoverseas, and the one for 400 kV has already been devel-

Figure 10 Rubber block insulator for 220-kV rating.

oped, so that its application area is growing. Moreover,aiming at simplification of installation work, we are presently developing a simplified termination which applies
rubber block insulator and oil to a termination, whereby
the 110-kV class has already been put into practicalapplication, while the 220-kV class is under development.
As for termination using new materials, on the other
hand, a composite-type termination has been developed,
which is based on composite insulator that consists of
FRP insulator and silicone rubber sheds instead of porcelain insulator. Because the composite insulator is lighter
than porcelain insulator, it is considerably advantageousin that the assembly work can be carried out safely in ashorter period of time without using heavy machinery.
With respect to electrical characteristics, it has been confirmed that the composite insulator is comparable to or
better than porcelain insulator due to the water-shedding
property of silicone rubber. While the composite insulator
has been applied to the 154-kV class presently, it isexpected that the application will grow to higher-voltage
regions in the future.
In addition, an insulation oil-free, 77-kV class dry composite type termination (see Figure 11) has been developed, which utilizes silicone rubber for the outer jacket
molded on an epoxy insulator. The termination is advantageous in that free-angle installation is allowed for; no oilleak occurs making it environment friendly; and jointing
work of cable takes only a short time because compact
versions of the CSJ mentioned above are used.
Introduction of dry composite type terminations to higher
voltage ratings has just begun, so that the application is
expected to expand in the future.
Furthermore, we have two kinds of compact joints,
namely: compact transition joint for different types ofcables such as the XLPE and OF cables; and compact Ybranch joint (see Figure 12) for three XLPE or OF cables.
These achievements have been realized by accumulating
design technologies, whereby the structural dimensions

Figure 11 Dry composite type termination for 77-kV rating.

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were reviewed for size reduction based on the new design
parameters obtained by improving the material and work
management.

3.

DISTRIBUTION ELECTRIC WIRES AND
CABLES

3.1 Underground Distribution Cable
Underground distribution cables range from 6.6 kV to 33
kV in voltage rating, and XLPE cables that employ crosslinked polyethylene as insulator are generally used. It may
be said that the history of XLPE cable is the history ofcountermeasures against water tree, a process of insulation deterioration due to water absorption. Water tree is aphenomenon in which water penetrates into insulation
under the influence of electric fields forming a dendritic(tree-like) array of voids filled with water, thereby degrading the insulation performance. Countermeasures against
this include: minimizing the foreign matters and voids
contained in the insulation, reducing the protrusions on
the interface of the insulation and relaxing the local concentration of electric fields. These can be realized by dry
cross-linking where cables are manufactured without
using water vapor pressure, by composing a layered
cable insulation where the inner and outer semiconducting layers are structured by semiconductive plastics
replacing conductive tapes, and by extruding the resultant semiconducting layers simultaneously with the insulation to carry out triple-layer extrusion. These countermeasures were implemented sequentially in the 1980s,
significantly reducing the occurrence of water tree deterioration since that time.
Moreover, water-impervious XLPE cables were developed and applied in the late 1980s centering on the 22kV and 33-kV XLPE cables, with the aim of improving thereliability further by completely preventing entry of water
into the cables. The water-impervious tape consisted of alaminated lead tape which is laminated with a lead foil
and plastics to improve the extensibility, making it possible for the tape to follow the thermal expansion and con-traction of the cable. This laminated lead layer was bonded on the inside of the cable sheath, constituting a waterimpervious cable. In the 2000s, we eliminated lead fromwater-impervious cables ahead of others intending to
make an environment-conscious cable. To this end, we
replaced lead on the water-impervious layer with aluminum to complete an aluminum water-impervious cable,
and we are promoting substitution of this cable for leadwater-impervious cables (see Figure 13).
3.2 Submarine Cable
High reliability is required for submarine cables, because
repair is difficult once they are laid. Although steel rods 6
to 8 mm in diameter are wound around the cable forarmoring purpose to prevent external damage, these steelarmor rods are often damaged in long-term service byelectric corrosion and the like due to ocean current andearth magnetism. To improve this disadvantage, application of corrosion-free FRP rod was investigated. As theresult, a composite steel and FRP armored submarine
cable was developed which combines the strength ofsteel rods and the corrosion resistance of FRP rods, andthe cable was laid between the main island and Izenajima
island in Okinawa in 2002 (see Figure 14). From thestandpoint of natural environment preservation, an arch

Aluminum waterimpervious layer

Figure 13 Aluminum water-impervious cable.

Water-blocking conductor
Conductor screen
Cross-linked polyethylene insulation
Insulation screen
Lead sheath
Polyethylene anticorrosion layer
Plastic yarn ﬁller
Binding tape with manufacturer's namePlastic yarn bedding
FRP with high-density polyethylene sheath
Plastic cushion cord
Hot-dip galvanized steel rod
Plastic yarn serving

Figure 12 154-kV compact Y-branch joint, measuring 300 mm x
600 mm x 1,500 mm.

Figure 14 Cross section of composite armored submarine
cable.

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horizontal boring method was adopted to protect thecoral reef at the both sides of foreshore, as the first application for domestic submarine cable.
3.3 Reduced Wind Drag Insulated Wire
Strength of supporting structures for electric wire facilities
such as electric poles is designed based on the loads
under the influence of wind pressure. With the aim of
reducing the construction cost by decreasing the design
load on supporting structures, studies on wind dragreduction have been conducted. Whereas the studies
have been conducted mainly for overhead transmission
lines conventionally, recent years have seen an expansion
to overhead distribution lines such as the OC (Outdoor
Cross-linked PE insulated) and OE (Outdoor PE insulated) wires, and the cross-sectional shapes of insulated
wire with reduced wind drug have been establishedresulting in practical applications.
Drag on a cylinder placed in a flow is generated as adifference between the windward pressure and the
reduced pressure called wake flow at the leeward, so thatthe principle of reducing the wind drag on wires consists
in reducing the wake flow, as shown in Figure 15. The
reduction of wake flow can be achieved by introducing
irregularities on the cylinder surface thereby displacing
the separation point of the boundary layer from the cylinder to the leeward as far as possible. Accordingly, reduction of wind drag on wires resides in finding out a surface
shape that offers efficient wind drag reduction. Our wire
shapes for reduced wind drag come in two types ofgrooved cylinder and regular polyhedron, and an optimized reduced wind drag design is available dependingon the type of wire and the applicable range of windspeed.

3.4 Recycling of Wire Sheath Materials
A recycling system is established for electric wire stocks,
in which copper used as conductor is recovered andreused in electric wires, and application of recycled aluminum to electric wires and the like is also making progress
thereby achieving a recycling percentage of nearly 100 %.
Moreover, we are developing jointly with Tokyo ElectricPower Company a recycling program of electric wire
sheathing material, which is targeted at a recycling percentage of 100% for electric wire. Main sheathing materials for electric wires to be recycled include polyvinylchloride (PVC), polyethylene (PE) and cross-linked polyethylene (XLPE).
(1) Recycling of PVC
PVC materials recovered from the removed OW (Outdoor
Weatherproof PVC insulated), IV (PVC insulated), DV(PVC insulated Drop service) and SV (Service entrance
PVC sheathed cable) wires have varied characteristics intheir roughened extruded surface, insulation resistance

Figure 16 Reduced wind drag wire with 30 grooves.

(1) Groove typeFigure 16 shows the shape with 30 grooves. This is targeted at smaller wires, and has come into use in practicalapplications in the range of 10 to 25 mm in diameter.
(2) Polyhedron typeFigure 17 shows the shape with a 19 to 20 faceted polyhedron. This has come into practical applications forwires having a diameter of 18 mm or above.
Figure 18 shows typical wind drag reduction. Comparedwith conventional cylinder wires, wind drag can be
reduced by 30 to 50 %.

Figure 17 Reduced wind drag wire with 20-faceted polyhedron.

1.4

Flow
Boundary
layer

Wake flow

Boundary
layer

Wake flow

Drag coeﬃcient

1.2
1.0
0.8
0.6
0.4
0.2
Separation
point

Cylinder (ordinary wire)

Separation
point

Reduced wind drag wire

Figure 15 Mechanism of wind drag reduction.

0.030-groove type

0

10

20

Polyhedron type

30

40

Existing wire

50

60

70

Wind speed (m/s)

Figure 18 Comparison of wind drag reduction characteristics.

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and degraded brittleness, so that it is necessary to takeproper measures before applying them to electric wires
again. Even though the recovered PVC materials are
kneaded after adding stabilizer and plasticizer so as toimprove their characteristics, the recycled materials arestill inferior to new materials such that it is difficult to apply
some specified color markings on their surface.
Accordingly, in application to wire sheathing, a two-layered structure is adopted: recycled material for the inner
layer and new material for the outer layer. The use of newmaterial on the outer layer makes it possible to distinguishphases by coloring, and the appearance becomes comparable to that of conventional wires. Thus, we haveachieved the reuse of recovered PVC material to electric
wire sheathing by means of material property management, improvement of recycling kneading techniques andthe adoption of two-layered structure. The recycling of
PVC is currently applied to the IV, DV and SV wires.
(2) Recycling of PE
As for the recycling of PE, recovered PE from OE wire ispelletized into recycled PE to be used in sheathing of OE
wire again. PE sheathing recovered from Tokyo ElectricPower Company ---colored in black by its nature containing weather resistant carbon--- was found to be rather
stabilized in the quality, so that it was concluded thatapplication to wire sheathing would pose no problems if
the quality of recovered lots are properly managed. The
characteristics of prototyped OE wires fully satisfied thewire specifications despite their somewhat roughened
surface. The recycled OE wire has acquired Tokyo ElectricPower Company’s type certification leading to continued
delivery. Also, the recycled PE material is being applied toplastic drums for wires, expanding its applications.
(3) Recycling of XLPEXLPE is a cross-linked polyethylene with improved heat
resistance. Cross-linked structure results in low fluidity
above the melting temperature of a material, capable ofsustaining the original shape. This made it difficult toreprocess the recovered XLPE using extrusion and thelike, so that conventionally recovered materials were disposed of as fuel by thermal recycling or as industrial
waste. We have developed a melt & shear kneading
method, in which suitable amounts of heat and shear are
applied to XLPE to break down the cross-linked structure
thereby reducing the molecular weight. In this way therecovered XLPE can be reprocessed using ordinary extrusion forming. Because the recovered XLPE is forcibly
reduced in the molecular weight, its mechanical characteristics like elongation are significantly lowered.
Accordingly, in applications to wire sheathing, the material
was mixed with virgin PE to improve the deteriorated
characteristics, and it was found that if the mixing ratio of
the recovered material is not more than 25%, the resultant
material is comparable to virgin materials. This recycledmaterial can be cross linked by either the water vapor orsilane cross-linking processes, and is applicable to OC
wire using regular manufacturing processes. This recy-cled OC wire also acquired a type certification from Tokyo
Electric Power Company, and was delivered to the same
company (see Figure 19).

4.

CABLE ACCESSORIES FOR
UNDERGROUND DISTRIBUTION

4.1 Joint for 6.6-kV XLPE Cable
Joints for underground distribution cables have everundergone changes to adapt themselves to the cablestructures of the times. Specifically after 1970, as XLPE
cables have evolved to become established, solder jointing of conductors has been replaced by compression
jointing using neither torch nor heat reducing jointererrors, together with prefabricated joints which need notape wrapping for insulation. As for 6.6-kV cables, suchjoints have come into practical applications and are widely used including slip-on type straight-through joints,
slip-on type terminations and porcelain bushing type terminations.
Since around 2000, cold shrinkable terminations havebeen used, with which, as shown in Figures 20 and 21,
the main body of a joint is expanded beforehand at thefactory over a supporting core, which is removed after
cable conductor jointing and insulation shaping to makethe main body fit on the cable. The main body uses silicone rubber having superior contamination resistanceand mechanical as well as electrical characteristics, withan aim to improve reliability and workability.
Intermediate joints such as straight-through joint andY-branch joint also use silicone rubber, and cold-shrinkable joints have come into practical applications in orderto reduce the number of parts and to improve workability.
The structure of Y-branch joint is such that a spacer
with a built-in electric stress relief function is mounted oneach core conductor, on which an insulation housing is
cold-shrunk. A waterproof spacer is mounted on the endsof two branches to waterproof them in block using awaterproof tape, aiming at workability improvement anddownsizing of the joint.
The Y-branch joint is practically applied in the field as acomponent of the so-called “soft” underground distribution cabling system. Conventionally underground installation of distribution cables required that a tower for circuit
breakers be installed on the ground for branching, thus
necessitating a certain width for the sidewalk. Application

Figure 19 OC wire using recycled material.

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of Y-branches, in contrast, allows for branching without
installing equipment on the sidewalk (see Figure 22).
In the beginning of the 1980s, cable connectors for
XLPE cables to circuit breakers and transformers began
to have a prefabricated structure, in which a premolded
insulation housing made of EP rubber is inserted into
equipment-side bushings molded with epoxy and thelike, taking advantage of rubber elasticity to maintain insulation performance. In the first half of the 1980s, separable
connectors for multi on-load switch and separable connectors for mold-dyscon were specified by Tokyo ElectricPower Company, and they became widespread nationwide. In the last half of the 1980s, as the gaseous circuit
breakers became popular, cable connectors wererequired to be small in size, so that T-type cable connectors were specified by the four electric power companies
headed by Chubu Electric Power Company, and thesecable connectors were extensively adopted.
4.2 Joint for 22-kV XLPE Cable
As for the 22-kV ratings, slip-on type straight-throughjoint using molded rubber insulation housing plus spacer(i.e., stress relief cone) came into use in the 1980s, andthe conductor connection method changed into compression connection. Thus the so-called prefabricated joints
have been extensively used for their stabilized performance until today.
In an effort to reduce the distribution equipment costs
by upgrading facility efficiencies, Tokyo Electric Power
Company has been promoting the expansion of the 22-

kV power supply system since the first half of the 1990s.
New cables and joints were required aimed at maintaining
reliable power supply and cost suppression, and in
response to this requirement, cables using aluminum
laminate tapes for water-impervious layer were developed
together with joints suitable for these cables. The cableouter semiconductive layer end treatment method on the
joint was elaborated to reduce the insulation thickness,
resulting in a reduction in the thickness from 7 mm to 4.5
mm (including the inner semiconductive layer). Thus acold-shrinkable straight-through joint with improved
workability on site has come into practical applications.
The new water-impervious structure has adopted a heatshrinkable tube with a built-in metal foil inside. The metal
foil is of aluminum taking environment-friendliness into
consideration, and it is sandwiched via adhesive layers
between heat-shrinkable polyolefin layers (see Figure 23).
4.3 Overhead Line Protector
We have developed a flame-retardant wire protector for
preventing overhead distribution wires from contactingwith trees, in which, unlike conventional ones, both ends
are colored in gray.
It has been reported that overhead distribution wires

Pole mounted transformer
Pole mounted transformer
Low-voltage
branch switch

Distribution
diagram

Roadway

Sidewalk

HousingHigh-voltage
branch switch
High-voltage
main line
Low-voltage
line

Supporting pole

Duct for lowvoltage main line

Y-branch joint
High-voltage
branch switch

Low-voltage
branch switch

Duct for highvoltage main line
低圧管路
Duct
for low-

Duct for high-voltage volotage line
branch for transformer

Figure 22 Conceptual image for installation of Y-branch joint.

Figure 20 6.6-kV cold shrinkable outdoor termination (mainbody).

7

4

4
1

2

5

6

7 3

Approx. 750① Conductor connecting sleeve⑤ Semiconductive paint② Insulation housing⑥ ACP tape

③ Grounding plate⑦ Waterproof tape

④ Water-impervious heat-shrinkable tube

Figure 21 6.6-kV cold shrinkable outdoor termination.

Figure 23 Cold-shrinkable straight joint with water-impervious
layer.

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can catch fire when they contact with trees, and accordingly, the Technical Standards for Electric Facilities specifies the use of double-layer structured wire protectors orabrasion-proof insulated wires. Because no flame-retardant specifications were applied to the prototyped wire
protectors, it was occasionally found that they catch fire.
To settle this problem, development of flame-retardantwire protectors was intended.
Flame-retardant polyethylene materials were investigated to achieve ample fire-resistance, and both ends werecolored in gray to make the protector distinguished fromconventional ones easy (see Figure 24). Before the adoption of gray-colored covers, 2,000 hours of Sunshine
Weatherometer tests were carried out together with accelerated weathering tests equivalent to 4,000 hours using a
Super UV Tester, thereby having confirmed the long-term
performance (see Figures 25 and 26).
As a result, it was determined that the characteristics
hardly changed even after 2,000 hours had passed, andthe product was released into the marketplace. Tokyo
Electric Power Company is introducing this productincreasingly.

4.4

Recycling of Removed Accessories from
Distribution Lines
In addition to the recycling of wire sheathing materials
described in Section 3.1 above, we are also studying
recycling of accessories removed from overhead distribution lines.
Disposing of accessories removed from overhead distribution lines results in an enormous amount of costs. We
began recovery of removed accessories aiming at reducing these costs and developing practical uses of recycledmaterials. Removed accessories at installation companies
come in a wide range: porcelain products, metal products, insulation products and packaging materials, so that
we asked the companies to sort the removed items
according to the list shown in Table 1 for our recovery.
Large-sized bags called FleCon (flexible container) aredistributed among branch offices of installation companies, and they are collected when filled up. But removed
accessories of large size are collected in the form as theystand. Collection efficiency can be improved by visiting
plural sites at a time (see Figure 27 and Table 2).

Table 1

Materials of removed accessories for recycling.

Classification

Material
Normal polyethylene
Flame-retardant polyethylene

Insulation cover

Polyvinylchloride
RubberWire protector

Normal polyethylene

Supporting wire protector

Normal polyethylene

Cable sheath

Polyvinylchloride

Binding wire waste

Residual tensile strength rate (%)

Figure 24 Overhead line protector.

CopperAluminum

120.0
100.0
80.0

Sunshine
Super UV

60.0
40.0
20.0
0.0

0

1000

2000

3000

4000

5000

Time (hr)Figure 25 Results of weather resistance test.
Figure 27 Removed overhead line protector.
Cover forﬁxed-side

Main body

Cover forinsertion-side

Table 2Company

300

Effectiveness of recycling.
Effectiveness of recycling

Installationcompany

Full awareness of sorting at sites

Furukawa
Electric

Improvement in R&D technology for recycled products

Enhanced sorting awareness of removed accessories
Product development using recycled materials

Figure 26 Cover for overhead line protector.

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Removed accessories collected in this manner areproperly sorted and pulverized for further applications
including reuse as a distribution line component, forwhich prototyping is underway. This program is attaining
good results in many fields and accordingly, we are
studying its feasibility as a business. There are concerns,
however, that removal, sorting and productization can be
costly for recycling the removed accessories, so that acomprehensive study that takes these factors into accountis needed.

5.

OVERHEAD TRANSMISSION LINE

5.1 Aluminum Conductor
In the beginning, aluminum conductors for overheadtransmission lines were manufactured from pure aluminum (ECAL), using wire rods made by the hot-rolling andextrusion methods. Later on, in response to the increased
demand for aluminum conductors, continuous castingand-rolling methods such as the Propelti method weredeveloped to improve productivity. During the 1960s and1970s, various aluminum alloys for electrical conductors
have been developed that are characterized by strength,heat-resistance and electrical conductivity, respectively.
In particular, a heat-resistant aluminum alloy conductor(TAL) with an enhanced power transmission capacity has
been developed in order to meet the rapidly increased
power demand at the time of high economic growth in the
1960s, and the conductor has been used in abundance
up to the present date. This was followed by the development of a extra thermo-resistant aluminum alloy conductor (XTAL) with much improved heat resistance, and a
60% heat conductivity super thermo-resistant alloy conductor (ZTAL) which realized improvements in both electrical conductivity and heat resistance; and both of them
have come to practical use. An electric power conductor
is configured using these aluminum alloy conductors suitably selected depending on applications, which arearranged around the central steel or aluminum-clad steel
wires to constitute a corrosion-resistant stranded wire.
Table 3 shows the properties of various heat-resistant,high-strength aluminum alloy conductors.

Table 3

Type

Properties of various heat-resistant, high-strength
aluminum alloy conductors.
Electrical
Working temperature (°C)
Tensile strength
conductivity(MPa)(% IACS) Continuous Short time Instantaneous

HAL

157~196

61

90

120

180

TAL

157~196

60

150

180

260

KAL

225~255

58

90

120

180

KTAL

225~255

55

150

180

260

UTAL

157~196

57

200

230

260

ZTAL

157~196

60

210

240

280

XTAL

157~196

58

230

310

360

5.2 OPGW
Optical ground wire (OPGW) is an overhead grounding
wire to effect grounding of overhead transmission lines, inwhich optical fibers are integrated to provide communication functions. OPGWs enable long-distance, high-quality
data transmission as well as video transmission without
being affected by electromagnetic fields in any way, sothat it is utilized as a transmission line for remote control
of unattended power plants and substations in addition tocommunications between power plants. Aluminum-cladsteel wires used in OPGWs are manufactured using conform extrusion. Conform extrusion technology allows forarbitrarily changing the thickness of the aluminum layer ofaluminum-clad steel wires, thereby having the wires withvaried electrical conductivities. We manufacture and supply OPGWs of various specifications that are tailored tothe diversified customers’ needs.
5.3 Trolley Wire
We manufacture power distribution wires (i.e., trolleywires) and feeders to supply electricity to electric railcars.
Trolley wires, commonly known as overhead wires forelectric railcars, are used to supply electricity to electricrailcars and the like, whereby electric railcars and electric
locomotives take electricity in by bringing their pantographs in contact with the trolley wire. Common electricrailroads use grooved trolley wires to hang them by grappling for installation. Requirements for trolley wires include
high tensile strength and superior abrasion resistance aswell as good electrical conductivity, and abrasion resistance is quite important for railway sections of heavy traffic, and accordingly we are also studying the improvement of abrasion resistance. Trolley wires made of silvercontaining copper with superior heat resistance are widely used for high-capacity applications.
Supplying electricity by means of trolley wire only can
result in usage of trolley wires too large in diameter, sothat separate electric wires having large current capacity
are installed in parallel, which are suitably connected tothe trolley wire to supply electricity. This electric wire,
called feeder, used stranded wires of hard copper conventionally, but recently aluminum stranded wires arewidely used.
5.4 Overhead Transmission Line
Overhead transmission lines have undergone distanceand capacity upgrading, and 500-kV lines have alreadybeen installed in succession, which has been followed by
1000-kV lines. For this market, we manufacture various
aluminum conductors such as steel wire core aluminum
stranded conductor (ACSR) and steel core heat-resistantaluminum stranded conductor (TACSR). Figure 28 showsa large stranding machine used for manufacturing.
To ensure reliability of these high-capacity overheadtransmission lines, it is essential that mechanical characteristics of multi-conductor lines be clarified such as galloping oscillation and subspan oscillation, and we havemade a significant contribution through experimentation
to the optimization of conductor and spacer spacing andFurukawa Review, No. 32

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to the validation and practical application of large-sizedaccessories.
In terms of environmental harmonization, we are studying to reduce wind noise on conductors, mechanism ofwhich is that a conductor exposed to wind generates
Karman vortices, which cause noise when they separate
from the conductor. We have developed a reduced windnoise conductor, which has protrusions on the surface todisturb the vortices thereby suppressing the wind noise,
and we have brought this conductor into practical use.
This reduced wind noise conductor tends to generatecorona discharge, when it is used in high-voltage transmission lines, due to water droplets adhering to the protrusions in rainy weather. Accordingly we have also developed a corona suppression technology, in which together
with enhancement of hydrophilicity of the conductor surface, improvement of the shape of protrusion lines provided at the outermost layer for wind noise suppression efficiently reduced the corona noise.
We manufacture anti-snow conductors that prevent
accretion of ice and snow, by mounting resin rings at regular intervals at the time of conductor manufacturing. Thisanti-snow conductor has the advantage of laborsaving at
the time of installation compared with the anti-snow ringwhich is manually installed on the existing lines using a
midair carriage, and moreover, the conductor is indispensable for small-capacity lines where midair carriages
are unusable because of the small-sized conductor.
Figure 29 shows the SL (snow-less) conductor and its
manufacturing facilities.
To make newly installed conductors which are very
shiny less conspicuous against the environmental background, low-reflectivity conductors with reduced luster
have been developed using the sand blasting process,together with low-brightness conductors having a surface
brightness matched to the background along the overhead line’s passage, and these conductors are used in
the national parks and the like.
As the line capacity is increased, the allowable temperature for usage of aluminum conductors is raised, resulting in an increase in the span dip of the conductor. To

suppress this increase in the span dip, super-thermo
resistant aluminum alloy conductors, galvanized invar
reinforced (ZTACIR) having invar wires of small linear
expansion coefficient at the core of its steel central members has come into practical use, along with extra-thermo
resistant aluminum alloy conductors, aluminum clad invar
reinforced (XTACIR). These conductors contribute to thedownsizing of the facilities because their use can avoid
bank raising and reinforcing of supporting towers.
In terms of construction method, prefabricated conductor stringing has been extensively implemented aiming atlaborsaving, whereby the length of a conductor is precisely measured at the factory beforehand, with a precision of 1/10,000 and taking the specified span dip into
account, and the resultant length is marked to enabledead-end clamp compression work of conductor at thedrum site. In recent years, complete prefabricated conductor stringing has come into practical use, in whichcable drums provided with an accommodation space forthe clamped portion of a conductor are used. This method allows for clamp compressing the conductor before
shipping, and accommodating the compressed conductor in a drum for delivery, thereby enabling shortening ofconductor extension time at the site.

Figure 28 Large stranding machine.

Figure 29 SL conductor and its manufacturing facilities.

5.5 Overseas Construction ProjectWith respect to the turn-key projects for construction of
new overhead transmission lines and the projects for liveline OPGW installation on existing overhead transmission
lines overseas, we are promoting marketing, bidding,sales activities as well as execution of projects. Marketingand project execution for the turn-key projects for construction of new overhead transmission lines worldwide istargeted mainly at extra-high voltage transmission lines
over 500-kV rating.
Live-line OPGW installation refers to replacement ofexisting overhead grounding wires by OPGW without
power shut-down. Conventional replacement work was tobe carried out under conditions of either single-circuit
power shut-down in case of a double-circuit transmission
line or full-circuit power shut-down in case of a single-circuit transmission line. However, in some electric powercompanies and government agencies overseas where
power grids are insufficiently established, it is very difficult

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to interrupt power transmission, or even when permitted,
to interrupt transmission for a long time, rendering
replacement to OPGW not easy.
We possess the installation technology to replace existing overhead grounding wires with OPGW while keeping
the overhead transmission line alive without interrupting
power transmission. We have carried out a total of 10,400
km of OPGW live-line installation in India, Malaysia, Iran,Philippines, Morocco, etc. Because this live-line OPGW
installation method uses hanging pulley blocks for
replacement of existing overhead grounding wires resulting in a very low stringing tension of no more than 1,000
N, it becomes possible to avoid using heavy-duty stringing machinery and to transport these machinery by manual transportation. This advantage makes construction ofpassageways for machinery transportation unnecessary
in case there is no access road to the site, leading to realization of installation in a shorter period of time. Table 4shows the features of the OPGW live-line installation
method.
Table 5 shows the overseas projects underway, andFigures 30 and 31 work scenes at previous overseas projects.
The world’s first OPGW live-line installation project
1,700 km in total length was planned in 1997 by Indian
electric power corporation PGCIL, and the tender specification was based on ground wire-wrapped optical fiber
cable (Wrap Cable) and All Dielectric Self-Support Cable(ADSS). We succeeded in adding, through presentation,
the brand-new OPGW live-line installation method we
had developed to the tender specification, received orderin 1999 winning an international competitive bidding, andcompleted the work in 2002 successfully, thereby acquiring customer’s satisfaction and confidence. Since then,we brought to perfection four projects of OPGW live-line
installation totaling 7,000 km in length in India as scheduled, and furthermore, based on the bid document prepared by a consulting company KEMA, the same as for
the Indian projects, we received jointly with ABB in

Table 4

5.6 Research & Development
At our Nikko Development Center, we conduct researchand development for products related with overheadtransmission lines to meet diversified requirements. This
laboratory is engaged in the research of wind noise, windload, corona discharge, snow accretion, galloping, size

Figure 30 OPGW live-line installation for 220-kV power transmission line in Teheran, Iran.

Outline of OPGW live-line installation.

Item

Description

Stringing tension

700~1,000 N

Stringing time

2 days/drum (3~5 km)

Applicable transmission line

66~500 kV

Table 5NationSwitzerland an order for the SCADA project of Philippine
NPC which included 1,500 km of OPGW installation in live
condition, and brought the work to completion with thecustomer’s satisfaction.
After that time, we have completed two OPGW live-line
installation projects totaling 2,000 km in Morocco, andcurrently, we are undertaking a live-line installation project in Senegal and simultaneously an OPGW installation
work in Bangladesh under the condition of single-circuit
interruption. As just described, our worldwide market
share for OPGW live-line installation accounts for 50%.
In the future, we intend to promote our marketing activities focusing on South Asia, Middle East, East Europe
and Africa.

Overseas projects underway.

VoltageLine length

Description

Malaysia 		500 kV

150 km Turn key-base installation of new transmission line

Egypt

		500 kV

216 km Turn key-base installation of new transmission line

South Africa 		765 kV

250 km Turn key-base installation of new transmission line

Bangladesh 220/ 132 kV 2,500 km

OPGW live-line installation

Sri Lanka

132/ 66 kV

105 kmOPGW live-line installation

Senegal220/ 90 kV

345 kmOPGW live-line installation

Figure 31 OPGW live-line installation for 275-kV power transmission line in TNB, Malaysia.

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reduction and environmental harmonization, since technologies to control these external environment elements
are indispensable for overhead transmission lines.
We have a low-noise wind tunnel for measuring windnoise and wind load on overhead conductors. The windtunnel was at first constructed for the purpose of windnoise measurement, and was used for the developmentof reduced wind noise conductors, but after a refurbishment to enable wind load measurement, was converted
for the development and productization of reduced windload conductors. The reduced wind load conductors havea drag coefficient (Cd value) 30% lower than ordinary
conductors, thus significantly contributing to the reduction of transmission line construction costs.
In the study of corona discharge countermeasures foroverhead transmission lines, corona noise and corona
hum noise from low noise conductors and jumper assemblies are investigated using the transformer and the corona cage (see Figure 32), both of which are applicable to
UHV ratings. We installed the above mentioned facilities
prior to the construction start of UHV transmission lines,
making a considerable contribution to the breakthroughand improvements of corona characteristics of UHV products, which led to the adoption of a number of our new
technologies and products in the UHV transmission lines.
When overhead conductors have snow and ice accretion under high winds, self oscillation with low frequency
and large amplitude (i.e., galloping) can occur, causing
interphase short circuits and considerable damage tosupporting structures. As a countermeasure for this, wehave developed a light and flexible polymer interphasespacer (SR interphase spacer) consisting of FPR rods
covered with silicone rubber molding, and the producthas been used in 66- to 500-kV overhead transmission
lines, proving its effectiveness.
Loose spacer is another countermeasure product. The
loose spacer is designed to give differing torsional rigidity
among multi-conductors so as to make the shape ofsnow and ice accretion nonuniform, thereby intentionallyrandomizing the lift forces acting on the windward andleeward in order to suppress galloping. Its structure is virtually the same as that of conventional bolt-less spacer,making it possible to suppress galloping simply by replacing conventional spacers with a loose spacer. We are also
developing simulation technologies to predict the effectiveness of such countermeasure products. At the OkuNikko UHV Test Line, we are making observations of galloping oscillation of overhead transmission lines toimprove the accuracy of the simulation software throughcomparison with observation data, as well as to validate
the effectiveness of the countermeasure products.
Moreover, we have released a lightning protector called“SR Horn” for overhead transmission lines, an applicationof our silicone rubber molding technology. Using direct
silicone rubber molding on zinc oxide elements, the products is lightweight and compact, and is applicable to 33to 500-kV ratings. It is necessary that lightning protectors
for overhead transmission lines satisfy the requirementsof growing demand and increasing voltage and therefore,
we are promoting research and development activities
under obligation to offer stabilized power supply.
Snow accretion to overhead conductors is an important
problem affecting the strength of supporting structures,short circuiting, earth faulting and sudden dropping ofaccreted snow, and accordingly, we have long been
studying the problem. As a result, we have released two
effective countermeasures of “anti-snow ring” and “antitwist damper”, which are currently in wide use for theirease of use and effectiveness. Indicator ring to preventthe collision of wild birds on the overhead conductors is
one of the application products of ring, improvement of
which is underway through effectiveness validation tests.
We are also studying snow melting wires as a countermeasure against sudden snow dropping, in which an FeNi alloy wire is closely wound around an overhead conductor to prevent snow accretion and sudden snow dropping by means of the heat generated by the conductor
current. To make the products effective even in the harshconditions in winter seasons, the magnetic material has
been improved to develop a high heat generation type.
The amount of wire winding depends on the current andambient air conditions, but usually results in a mass
increase of approximately 1 kg/m, so that partial application over the span or countermeasures against theincreased loads are implemented in some cases. We plan
to develop new lightweight products for snow melting.
Electric power companies are addressing the investigation of deterioration of aluminum conductors as a part offacilities maintenance program, and accordingly, we provide engineering services to analyze and evaluate thedegree of deterioration of removed aluminum conductors.
It is said that construction of large-scaled overheadtransmission lines will be settled for the time being whencurrently planned projects are completed in a few years,
and efforts will be focused on the maintenance activities
of existing facilities, where further laborsaving is required.
In response to such needs, we plan to concentrate on the
research and develop of new products related with maintenance work.

Figure 32 UHV corona cage.

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6.

ACCESSORIES FOR OVERHEAD
TRANSMISSION LINES

6.1 Oscillation Analysis Technology
We have been carrying out observations of an oscillation
phenomenon called galloping ever since we constructed
the Mogami Test Line (see Figure 33) in Shonai-machi,
Higashi-tagawa-gun, Yamagata prefecture. Galloping is
one of the peculiar aerodynamic phenomena seen in winter seasons, where more specifically, overhead conductors with snow or ice accretion oscillate in large amplitudes in the vertical plane when the wind speed and windvelocity meet certain conditions.
Because, if the oscillation amplitude increases, it is possible that the conductors will come into contact with eachother thereby causing short circuit accidents, clarifying its
mechanism in an effort to prevent accidents is a very
important task for appropriate maintenance of electric
power facilities. Accordingly we have been addressing
this problem since 1979.
The vicinity of Shonai-machi is provided with suitableconditions for occurrence of galloping due to the local
wind called “Kiyokawa-dashi” that blows almost throughout the year. Because snow accretion is the absolute condition for occurrence of galloping, we use a “mock accreted snow” (see Figure 34) that can achieve equivalenteffects during snowless seasons to forcibly generate galloping.
This test line is characterized by its unattended observation operation using our proprietarily developed system, in which measurement data such as wind direction,wind velocity, conductor tension and conductor displacement are transferred in real time to our laboratory locatedin Nagai-city. The obtained data are input to simulation
software to achieve comparative analysis between theactual measurements and the simulated results, enabling
improvement of simulation technologies as well as application to development of countermeasure products. Our“loose spacer damper” that has received a lot of inquiries
from electric power companies is one of the representative examples (see Figure 35).
Airflow simulation software has also been introduced
since last year, which predicts wind behavior at any location with specific geographical features when the longitude and latitude of that place are given. Combining thissoftware with the one for oscillation analysis will enableimproving the accuracy of oscillation analysis as well as
simulating wind behavior at an arbitrary spot on a powertransmission line. Since these techniques, together withthe mechanical deterioration data such as fatigue degree
and wear amount that have long been accumulated,make it possible to predict the progression of products
deterioration, it is expected that they will lead to creationof a new customer service like making suggestions for
replacement life time of products.
6.2 Deterioration Prediction Technology
The causes of deterioration of overhead conductors may
be divided into two categories: one is mechanical deterioration which is caused by loads due to oscillation and thelike, and the other is electrical deterioration in which electrical resistance increases at electrical connections underapplication of current. While we are involved with both of

Figure 33 Panoramic view of Mogami Test Line.

Figure 34 Installed “mock accreted snow” to simulate snow
accretion.

Figure 35 “Loose spacer damper” for four-conductor overheadtransmission lines.

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these categories, we will present here the prediction technology for electrical deterioration because our activities
related with mechanical deterioration overlaps with thedescription in Section 6.1 above.
Generally speaking, compression joint tubes for aluminum conductor have an intrinsic problem in that theirelectrical resistance more or less increases by use overtime. Increase in electrical resistance is nothing short ofimpeding current flow, and the jointed portion is heated
due to Joule heat. The larger the current, the higher thetemperature rises, resulting in melt down in the worst
case. For this reason, electric power companies consider
inspection of compression joint tubes is a maintenancemanagement job of the utmost importance.
Against this background, we have long been engaged
in the study of this technological field. In the preliminary
stage of the study, we gathered a maximized number ofremoved products from every electric power company,
making efforts to accumulate fundamental data including
the correlation between usage period and electrical resistance. In the medium stage, based on these data, wehave set up a hypothesis concerning the electrical deterioration, and succeeded in validating the hypothesis
through accelerated deterioration tests and the like.
Currently, we are addressing the joint development of“Deterioration Simulation System” with some electric

power companies to integrate our study (see Figure 36).
To be more specific, samples are taken from overheadtransmission lines, their initial electrical resistances arecompared with those at the time of inspection to understand the present degree of deterioration, and thereby
simulating, based on the data and knowhow which havebeen enormously accumulated, what degree of deterioration is anticipated in the future. It is thought that this system contributes, when completed, not only to prevent
melt-down accidents but also to reduction of maintenance and inspection costs, because it will help us to reasonably make out a schedule of inspection cycle andrefurbishment time.
Furthermore, “Bypass Device” (see Figure 37) and“Fusion Joint” (see Figure 38) that have been developed
during the course of this study have been employed by anumber of electric power companies. In particular, theFusion Joint was highly appreciated for its unique idea,
and was awarded jointly with an electric power company
in 2005 a “Shibusawa Award” which is intended for inventions that have achieved a strong performance in the fieldof electrical safety.
6.3 Casting Technology
We manufacture some of aluminum castings in-house
while enjoying our proprietary casting knowhow solely in
the industry. Our casting method is gravity die casting
comprising greensand mold casting and metal mold casting. Greensand mold casting is carried out at outsidecompanies headed by our affiliate company, while metal
mold casting mostly in-house.
We deal mainly with Al-Mg-based AC7A, Al-Mg-Sibased AC4C-(H) and pure aluminum. Every material has
its specific features. For example, AC7A has superior corrosion resistance and mechanical characteristics, while its
castability is insufficient. Pure aluminum is not stipulated
in the JIS standards for castings, making itself a very special material specific to the industry. Its solidification
behavior is quite different from other materials, thus
requiring a unique mold design. Material selection isdetermined depending on the characteristics of the prod-

Figure 36 Display in “Deterioration Simulation System” underdevelopment.

Figure 37 “Bypass Device” for stagnant electric current.

Figure 38 “Fusion Joint”, where conductors are welded without
forming an electrical connection.

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uct to be manufactured. In this context, products manufactured by casting of pure aluminum unexceptionallybelong to, as represented by compression dead end
clamps (see Figure 39), the family of compression joint
tubes aimed at electric current conduction, so that caremust be taken in casting such a material of poor castability.
Since this industrial field is the most susceptible toadverse influences of the exodus of the baby-boom generation, there is an urgent need for constructing a new
system that combines “high technology” and “experience” for handing down the technology, and accordingly,
we are addressing such a problem.
Our casting technology has gained ground not only
domestically but also overseas. In 2004, Shanghai-Asahi
Electric Works Ltd., our affiliate company in China
received an order for aluminum cleats made of AC7A (seeFigure 40) for use in 110-kV power cables to be laid along
Donghai Bridge in Shanghai, and we provided them withtechnical assistance. At that time, there was virtually noplant in China that could cast AC7A, the most difficult aluminum alloy to cast, so that the technical assistance covered an extensive area comprising plant layout, selectionof facilities, design of molds, casting through machining,assembly, inspection and quality control. Thanks to thesincere attitudes of local workers to follow what theylearned, they succeeded in achieving the same productlevels as for the domestic counterparts. Today, they still
keep a high quality level, and their products are not only
delivered in China but also exported to Japan.

7.

INDUSTRIAL CABLE

The business fields of industrial cables cover a wide
range of applications including industrial plants, buildings, ordinary houses, railway rolling stocks, ships andindustrial machinery, so that varieties of electrical wires
and cables are developed and supplied in response to
the service conditions and required performance. We
develop, in addition to wires and cables, cable accessories and special functional products, which have acquireda favorable reputation.
7.1

Electric Wire for Industrial Plants and Building
Facilities
To deal with global environmental problems, regulationtightening against hazardous substances is accelerated
in the business field of electric wires as well. Whereas
conventionally, lead-based stabilizers were generally
used for PVC that has been extensively used as an insulating and sheathing material for electric wires and cables,
we have eliminated lead not only from the IV (Indoor PVC)
and HIV (Heat resistant Indoor PVC) wires for distribution
boards and equipment, but also from general purpose
cables like XLPE and CVV (Control PVC PVC), thereby
proactively promoting the elimination of hazardous substances.
Moreover, Eco-material wires and cables in which PVC
is replaced by flame-retardant polyethylene to make themenvironment-friendly, which emits neither hazardous halogen gases nor large amounts of smoke when combusted,
are in widespread use centering on government and otherpublic offices. We develop and supply wires and cables
according to specifications best suited for the service
conditions and required performance, based on thedesigns such that a UV-resistant, flexible material isapplied to the EM-EEF/F cable substituting for conventional VVF, and also a material of superior mechanicalcharacteristics is used for the EM-CE/F cable for power
applications (see Figure 41). Furthermore, in the processof promoting the clean technology for Eco-material wires
and cables, we have succeeded in developing a “lower
outgas cable c901” for use in clean rooms where liquid
crystals and semiconductors are handled, achieving
excellent delivery track records. This is a new product that

Figure 39 Compression dead end clamp, a typical product ofpure aluminum.

Figure 40 Aluminum cleat made in China.

Figure 41 UV-resistant flexible ECO wire “EM-EEF/F”.

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has reduced the organic gases (outgases) emitted by thecable to one tenth or lower than the general-purpose
ECO cables.
7.2 Electric Wire for Railway Rolling Stocks
The amount of electric wire for in-vehicle use is increasing as computerization in railway rolling stocks advances,accompanied by the requirement for decreasing the size
and weight of the wires to reduce the wiring space andweight. We have developed the so-called “compact wire”
that has reduced the insulation thickness to less than half
the conventional electric wires for railway rolling stocks(WL1 and the like). The wire has, despite their thin insulation, superior mechanical characteristics such as abrasion
resistance and cut-through resistance in addition to longterm reliability under varied environmental conditions,thus having been adopted by many customers.
Electric wires for subway vehicles are required, with an
aim to ensure safety within a tunnel, to be halogen-free
so as to suppress emission of hazardous gases andsmoke when combusted. In response to this requirement,
we have developed “low-smoke emission, halogen-free,compact wire”, and the demand is growing.

many customers, in which optical fibers are integrated for
ITV image and data transmission. However, optical connection of fibers in the optical fiber-composite cable tooptical transmission equipment mounted onboard posesa problem such that it is impossible in principle to adopt
slip rings based on metal cables, and that optical rotary
joints known as an optical coupling method cause coupling loss increases and loss variation. In this context, aninnovative optical coupling device “SC-BOX” we havedeveloped is based on an optical accumulator method,whereby one end of a multi-fiber optical fiber tape (withsix to twelve fiber counts) is fixed to the central fixed axis
to be spirally wound, while the other end is rotated as thecable reel rotates. This enables transmission of opticalsignals in a completely coupled state with the least coupling loss, so that the device has accumulated a numberof delivery track records for its high reliability in signaltransmission.

7.3 Cable for Electric Equipment of Ships
As ships advance in capacity, speed and automation to
improve the efficiency of marine transportation, cables forships are required to offer higher performance.
Responding to this requirement, we have developed“medium-voltage cable for ships” and “halogen-free,highly flame-retardant cable for ships” provided with highreliability, and the delivery has begun. Recently, we havealso developed “compact cable for ships” that has
removed metal braid armor from conventional wires aiming at weight reduction, making a contribution to weight
reduction and speed increasing for ships.
Against such a background where requirements forcables for ships have attained greater sophistication, IEC
standards for cables for ships have been revised, andaccordingly, we are actively making provision for revisionof JIS standards.

7.5 Medium Voltage Rubber Insulated Cable
While most of the electric power circuitry in Japan use
XLPE cables when they exceed the 6-kV class rating,demand for medium voltage cables provided with higher
flexibility than XLPE cables is growing in order to copewith the application conditions such as cabling in limited
spaces and cabling inducing bending and twisting, which
is often caused by cabling works for power capacity
upgrading in ships, wind-power generation facilities andpower supply systems between land and ships. We havedeveloped, taking advantage of the technology and experience we have accumulated for conventional 6-kV classcabtire cables, a series of medium voltage EP rubberinsulated cables in response to the individual requirements. We have established product lineups for both ofthese cable categories, and the delivery is expanding. As
for medium voltage EP rubber-insulated power cables
together with their accessories, we are promoting
research and development. Specifically, specifications fortheir termination joint materials have been studied aiming
at weight reduction and a completely dry system, and thefinal evaluation is underway to finalize the development.

7.4 Cabtire Cable
Mobile cabitire cables for supplying 100-V to 6-kV powersources and controlling various equipment are in widespread use in heavy-duty outdoor material handlingmachinery installed at harbor piers, raw materials stockyards of steel plants and the like. These cables for mobile
use are required to be provided with superior tensile force
resistance, bending resistance, twist resistance and soon, because they are subjected to repeated mechanicalstresses under the harsh environments at the site. We
have developed, by achieving an excellent structure
design, a cabtire cable for mobile machinery named“TraCab” (see Figure 42) with outstanding endurance tooffer a best-suited cable depending on application,acquiring a favorable reputation from our customers.
Recently, besides voltage increases in these cabtire cablelines, “optical fiber-composite TraCabs” are used among

Figure 42 Cabtire cables.

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Underground Power Cable, Distribution Cable, Overhead Transmission Line, Industrial Cable and Their Accessories

7.6 TV Camera Cable System
In the broadcasting industry, contents upgrading aimed at
high-definition images is advancing. Because it is impossible to transmit these contents using coaxial cables, conventional systems are rapidly being replaced by transmission systems using optical fibers. We have developed an
optical fiber-composite TV camera cable system of highstrength and flexibility together with optical connector
assemblies that combines ease of use with high endurance and high reliability that are indispensable for operations at broadcasting fields. This cable system has
acquired a high reputation not only from domestic but
also overseas customers, making a significant contribution to digitization and high definition imaging in the
broadcasting industry. Highly flame-retardant cables andlow smoke emission cables in compliance with theJapanese, European or U.S. standards have also beendeveloped, in response to the individual customers’
requirements (see Figure 43).

7.7 Joint Materials for Low-Voltage Cables
Because the tape winding method conventionally used
for branching and jointing cables at the construction sites
necessitated good skills and experience as well as considerable work time, there is an increasing requirement
for a method that offers simplicity and assuredness. Our“EfTouch Cover” (see Figure 44) has been developed tosatisfy such a requirement while offering a short-time,assured jointing work necessitating no skill. With thisjointing kit, the jointing work can be completed simply by;after jointing the conductor, one layer of self-bonding
insulation putty sheet is wound around the conductor toform an insulation layer in a manner such as for clay
work; a protection cover cut into half is placed to cover
the putty work on the joint; and the cover is fixed using an
attached belt. Because the kit can shorten the work time
significantly, it has acquired a good reputation among thecustomers, achieving satisfactory results year by year.
Moreover, all-purpose jointing materials kit “CellPack”(Figure 45) is also available to offer high water-tightness
and mechanical strength independent of the installation
environments. CellPack is a resin injection-based jointing
kit, featuring the use of a binary liquid mixture of low curing temperature and low contractility, and can be used invarious cable jointing works including the low-voltage
power, control, instrumentation, telecommunication, fireresistant and flame-retardant cables. While only a resin
injection method using a funnel was available conventionally, “CellPack CC” with which the resin can be directly
injected to the inlet on a closure recently joined the product lineup. CellPack has been extensively used in various
countries across the world for its ease of use and highreliability, achieving a track record of more than four million kits in total sum.

Figure 43 Optical fiber-composite TV camera cable system.

Figure 44 EfTouch Cover.

Figure 45 CellPack.

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Underground Power Cable, Distribution Cable, Overhead Transmission Line, Industrial Cable and Their Accessories

7.8 Special Function Products
We offer to the marketplace various products featuring
special functions as well as cables.
“DryKeeper” (see Figure 46) is a new type of absorbent
compound material provided with a humidity controlling
function, consisting of a high-performance water-absorbing polymer and a rubber of our proprietary blending.
Thanks to its reversibility such that it absorbs humidity inhumid environments, while emitting humidity in dry environments, DryKeeper can maintain a constant humidity
controlling function for a long time. In electric facilities likeswitch board installed outdoors, electric trouble and rusting due to dew condensation occurs from time to time,
thereby causing a maintenance problem. But DryKeeper
can suppress dew condensation for a long time taking
advantage of its humidity controlling function. DryKeeper
preserves its function for several years, more than ten
times longer than the conventional drying agents such as
calcium chloride and silica gel, thus contributing a great
deal to make electric power facilities maintenance-free.
“Joint unit for street light wiring” (see Figure 47) is aunit-type wiring system developed as a wiring equipment
to be installed in street light poles. With its structure filledwith molded resin, the joint unit protects the breaker andthe wired portion from humidity and dew condensation as
well as enables jointing of the power source with equipment outside the lighting pole, thereby achieving substantial laborsaving. Thus the joint unit is an innovative wiring
system that has solved the long-standing improvementtarget of dew condensation prevention and work performance improvement simultaneously, and its delivery is
expanding.

8.

CONCLUSION

We have long been developing the technologies for electric wires and cables together with their accessories in the

Figure 46 DryKeeper.

Figure 47 Joint unit for street light wiring.

electric power industry. It is anticipated that there will be a
growing need for safety, environment preservation andlow price in the future. Accordingly, we think it is our
responsibility to promote developing innovative technologies, thereby contributing to society.

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