NEWSFRO

M

JA

PA

N

Table 1. Some important physical properties of carbon fiber
Fundamental physical properties
Item2002

RecentRaw material

PAN1 carbon fiber

PAN carbon fiber

Tensile strength (N/mm2)

3,630

4,900

Elastic modulus (N/mm2)

235,000

235,000

Elongation at fracture (%)

1.5

2.1

PAN = polyacrylonitrile.

1by Y. Ohki
Development of a Low Sag Carbon Fiber
Reinforced Aluminum Conductor forTransmission Lines
The demand for electric power in the world is growing
steadily, especially in China. Electric power transmission capacity must, therefore, be increased. However, construction of newtransmission lines requires time and space and is costly. Towers
for overhead transmission lines are expensive, compared withthe cost of the cables. It follows that, if possible, the transmission capacity of overhead transmission lines should be increased
without changing the tower structures.
Another problem with overhead transmission lines is thelimited clearance between the transmission line and the ground,buildings, trees, etc. A heavy transmission conductor forms acatenary because of its weight. The sag increases if the conductor material has low tensile strength and a high thermal expansion coefficient. Increasing the current through an overhead line
increases its temperature and its length, and thus the sag, which
in turn reduces the ground–line clearance. To alleviate this prob-lem, a new aluminum conductor for overhead transmission lines
has been developed by Showa Electric Wire and Cable and Tokyo Rope Manufacturing, Japan [1]. It is called aluminum conductor fiber reinforced (ACFR). A key component of the ACFR
is the unique stranded carbon fiber reinforced plastic or carbon
fiber composite cable (CFCC), shown in Figure 1.
Table 1 lists some fundamental physical properties of thecarbon fiber used in the CFCC, and Table 2 compares the characteristics of CFCC with those of its conventional counterpart,
namely aluminum conductor steel reinforced (ACSR), each witha cross-sectional area of 160 mm2. As listed in Table 2, CFCC
has several advantages, contributing to the outstanding performance of ACFR. Compared to ACSR, CFCC has about one-fifth
the weight, one-tenth the thermal expansion coefficient, and ahigher tensile strength. It contains only nonmagnetic materials
and, therefore, does not suffer from magnetic losses. It is highly
flexible so that it can be wound around a small drum and is highly resistant to corrosion, unlike iron and steel. Last, its expected
creeping deformation level at high temperatures is similar to thatof iron.

Figure 1. Carbon fiber composite cable (CFCC) component (left side). Flexible CFCC (right side).
1 × 37 40.0φ = one strand with an outer diameter of 40 mm consisting of 37 wires; U = consistingof only one wire; Z = outermost wires are stranded like a letter Z, otherwise they are stranded likea letter S.
54

IEEE Electrical Insulation Magazine

Table 2. Comparison of various characteristics of the carbon fiber composite cable (CFCC) core of aluminum conductor fiber reinforced and the steel core ofaluminum conductor steel reinforced, both with a cross-sectional area of 160 mm2
Characteristic
Item
Heat resistant grade

CFCC

Steel

Normal/high temperature resistant—Cross section (mm2)

37.2

37.16

Outer diameter (mm)

7.8

7.8

Unit weight (g/m)

61

291.3

Rated tensile strength (kN)

79.5

44.2Elastic modulus (N/mm2)

130,000

Coefficient of thermal expansion (× 10−6/°C)

206,000

1.011.5

Figure 2. Cross-sectional structures of the conventional aluminum conductor steel reinforced(ACSR; a) and the developed aluminum conductor fiber reinforced (ACFR; b). CFCC = carbon
fiber composite cable; TAl = thermally resistant aluminum.

Table 3. Specifications of aluminum conductor fiber reinforced (ACFR) and aluminum conductor steel reinforced (ACSR) for low-loss operation
Conductor

Unit

ACFR

ACSR

DiameterConductor

mm28.6228.62Coremm

9.69.54Aluminum cross-sectional area

mm542.4

428.9

Linear mass

kg/m

1.597

1.621

Tensile modulus

GPa

68.6

78.4Conductor

× 10−6/°C

18.9

19.5

Core× 10−6/°C

1.011.5

Electrical current

A700

700

Operation temperature

°C

6773

AC resistance at operating temperature

Ω/km

0.06230.0851

Thermal sag at operating temperature

m

20.74

21.29

2

Thermal expansion

November/December — Vol. 33, No. 655

Table 4. Specifications of aluminum conductor fiber reinforced (ACFR) and aluminum conductor steel reinforced (ACSR) for high-capacity operationConductor

UnitACFR

ACSR

Conductor

mm28.62

28.62Coremm

12.5

9.54

Aluminum cross-sectional area

mm2494.5

428.9

Linear mass

kg/m

1.517

1.621

Tensile modulus

GPa

71.5

78.4

Conductor

× 10−6/°C

16.9

19.5

Core

× 10−6/°C

1.0

11.5

Electrical current

A

1,571

729

Operation temperature

°C

17575

AC resistance at operating temperature

Ω/km

0.09230.0858

Thermal sag at operating temperature

m20.74

21.29

Diameter

Thermal expansion

CFCC was developed in the 1980s. Initially, it was used forcivil engineering applications such as bridge reinforcement because of its anticorrosion properties. Then, after substantial testing by a Japanese electric power utility company, CFCC wasfirst used as the cores of ACFR conductors in 2002. In that role
it has now been operating satisfactorily for 15 years.
The structures of ACFR and ACSR are compared in Figures 2and 3. The ACFR is a composite consisting of a CFCC core andtrapezoidal-shaped annealed aluminum wires. It is also available
with hard drawn and heat resistant aluminum. The conventionalFigure 3. External appearance of aluminum conductor steel reinforced (ACSR) with a cross-sectional area of 160 mm2, andaluminum conductor fiber reinforced (ACFR) with a similar diameter.
56

ACSR consists of a steel core and round aluminum wires. TheACFR has lower electrical resistance than the ACSR, since thetrapezoidal shape has a larger contact area than the round shape.
Table 3 lists the specifications of ACFR designed for lowtransmission loss. The lightweight CFCC core allows an increased aluminum content, at constant conductor weight. The
transmission loss expected from this design is 27% less than thatof similarly sized ACSR because of the increased content of aluminum, zero magnetic loss, and high electrical conductivity resulting from the use of trapezoidal-shaped annealed aluminum.
Table 4 lists the specifications of ACFR designed for hightransmission capacity. Since the CFCC core has a small thermal expansion coefficient at temperatures as high as 175°C, its
thermal expansion is less than that of ACSR. The transmission
capacity expected from this design is more than double that ofsimilarly sized ACSR. According to the company, this format isvery popular worldwide because customers can increase transmission capacities using existing towers.
The company has been promoting the installation of ACFR
lines for long-term use, as shown in Figure 4. Initially, ACFR
would be installed as a low loss conductor. If the electric power
demand increased significantly, the ACFR conductor could beswitched to a high capacity conductor. Given further increasein power demand, an additional low loss conductor could be installed, and if appropriate, the high capacity ACFR conductor
could also be replaced with the original low loss conductor toreduce energy loss.
Figure 5 shows a tension clamp used for ACFR, consistingof three components. It is very similar to those widely used forACSRs. Since CFCC is stranded, the bendability and flexibilityof ACFR are good. ACFR is therefore easily handled by sucha clamp, and no special equipment is required, unlike several

IEEE Electrical Insulation Magazine

Figure 4. Installation of aluminum conductor fiber reinforced (ACFR) lines for long-term use.
many forums, e.g., CIGRE workshops, aiming to increase installation safety levels.
It is true that several pultrusion bar types of carbon-fiber-reinforced plastic cores for power transmission lines are available
from other companies. However, the most important feature of
the products described in this column is the stranded structure of
the core. ACFR with a CFCC core is significantly more flexible
and bendable than other conductors with a pultrusion-bar-type
carbon-fiber-reinforced plastic core.
This article was completed with the help of Tokyo Rope
Manufacturing Co. Ltd.

Reference
Figure 5. A tension clamp for aluminum conductor fiber reinforced.

[1]

F. Sato and H. Ebiko, Development of a Low Sag Aluminum Conductor
Carbon Fiber Reinforced for Transmission Lines. CIGRE 22-203, 2002.

other high capacity type conductors, e.g., carbon and glass fibercores. This makes the installation of ACFR very easy.
Many tests have been conducted to check the performanceof every component of ACFR under tensile loads, aeolian vibrations, corrosion resistance, sheave testing, and long-term
thermal aging. Satisfactory results were obtained. Recently, thecompany has described its preferred installation procedures inNovember/December — Vol. 33, No. 657