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TR/01/18

CIGRE 2018

Revamped High Ampacity Low Sag Stranded Carbon Fiber Composite Core –Aluminium Conductor Fiber Reinforced Conductor (ACFR)
OGOSHI RYUTA
Tokyo Rope International Inc
Japan
Ogoshi.ryuta@tokyorope.jp

SUMMARY
Globally ACSR and AAAC conductors are commonly used as overhead conductors for energy
delivery application. High density transmission corridors are the need of energy utilities to optimise
the right of way. So the use of High Ampacity Low Sag conductors (HALS) has been increased toaddress the increasing congestions in the existing transmission network. There are several types of
HALS conductor technology are tested and deployed by all major global power transmission utilities.
The selection of suitable HALS technology considering the requirements with respect to increase inpower transfer capacity, exiting ground clearance, existing tower loadings and cost of capital
investment is not only the deciding factor but also the operational efficiency (ohmic losses) over a
period of its life time and installation of those conductors in the existing terrain are the major
parameters needs to be considered for the right technology adoption.
Now a day, the carbon fiber composite core conductor technology has been preferred by the utilities
among the HALS conductor technology because of high strength to weight ratio, lower thermal
expansion and no creep (almost zero creep). The popular composite core technology are mostly asingle core or several number of single wires bunched together. But the challenges of this popularcarbon fiber composite core conductor technology is flexibility, which needs careful handling and careneeds to be taken during installation. After several years of research to address the challenges in thecarbon fiber composite technology we developed a technology to strand the carbon fiber composite
material to form a stranded carbon fiber composite core (just like stranded steel core used in ACSRconductors) to make it flexible and easy to handle during installation. This paper describes about thedevelopment, testing, deployment and applications of the revamped carbon fiber composite core
conductor technology named as Aluminium Conductor Fiber Reinforced Conductor (ACFR)KEYWORDSHTLS Conductor, Carbon fiber composite core, ACFR, Reconductoring transmission line,Carbon composite core conductor, High ampacity conductor, High performance conductor

11.

INTRODUCTION

The research and development to strand the carbon fiber composite material to make it more flexible
started in the year 1980’s . The stranded carbon fiber composite material is named as Carbon Fiber
Composite Cable (CFCC).The CFCC was first tested for civil construction application mainly
focusing to replace the steel reinforcement with CFCC to enhance corrosion resistance. The first
deployment of CFCC for civil construction application was PC bridge project in Japan in the year
1986. In the year 2002 the CFCC was used instead of steel core in the overhead conductor application,
the new conductor with carbon fiber composite core named ACFR was introduced, tested anddeployed in one of the transmission line project in Japan. The ACFR conductor was analysed to be thebest fit for overhead line which doesn’t have magnetic effect in the AC resistance (where as steel corehas its magnetic effect in the AC resistance), light weight, high strength, low thermal expansion andincrease in corrosion resistance.
The ACFR conductor construction is as simple as ACSR conductor where the stranded steel core isreplaced with stranded carbon fiber composite core. The outer conductive layer is a either a EC grade
hard drawn aluminium wires used in ACSR conductor or thermal resistance aluminium wires of eitherof Al-Zr alloy (Thermal resistance aluminium alloy) or EC grade thermal resistance annealed
aluminium wires. The selection of outer conductive layer depends on application and the preference ofthe energy delivery utilities. The annealed aluminium wires having little higher electrical conductivity
than the hard-drawn aluminium wires used in ACSR conductors, but annealed aluminium wires aresofter and are more prone to abrasive resistance and needs more care during installation. Thermal
resistance aluminium alloy (Al-Zr) having marginally lesser or equal conductivity as that of harddrawn aluminium wire and easy to handle as that of hard drawn aluminium wires used in ACSR
conductor. The conductive layer of ACFR can be of round wire or shaped wire (Trapezoidal, Z Shapeetc) to increase the conductive area. The trapezoidal wire shaped construction of ACFR conductor isshown in the Figure -1

Figure-1 Construction of ACFR conductor

2.

CFCC CORE

The raw material carbon fiber and epoxy resin matrix are bunched together to form acomposite wire and are coated with organic layer act as galvanic protection and thus formed
single carbon fiber composite wires are stranded together to form a stranded Carbon Fiber
Composite Cable (CFCC). The single strand size can be chosen to match the final CFCC
diameter suitable for ACFR conductor that replaces the existing conventional conductor.
CFCC has the same advantage as that of the single carbon fiber composite core like higher
strength, lower weight, lower thermal expansion and higher corrosion resistance. But theunique stranded carbon fiber composite core CFCC address the challenge of flexibility andhandling issues in the single strand carbon fiber composite core. The table-1 compares thesteel core and CFCC properties
2

Table–I Compression of CFCC and Steel core used in ACSR conductor
Properties
Construction (No./mm)
Type
Diameter (mm)Cross sectional area (Sq.mm)
Ultimate Tensile Load (kN)
Weight (kg/km)
Thermal expansion (x10-6 peroC)

3.

CFCC
7/3.2
CFCC
9.6
56.27
121931

Galvanised Steel (IEC)
7/3.2
Regular
9.6
56.27
69441
11.5

ACFR CONDUCTOR

The maximum continuous operating temperature of ACSR conductor is between 70oc to 90oc.
The limit of maximum operating temperature is considering the loss of strength of EC grade
hard drawn aluminium wires. So the current carrying capacity of ACSR is limited because ofjoules effect. The sag of ACSR is higher because of higher steel weight and higher thermal
expansion of steel.
The ACFR conductor uses high thermal resistance aluminium alloy or high thermal resistanceEC grade annealed wires, so the maximum operating temperature of ACFR is 180oc. Themaximum operating temperature of ACFR is restricted considering the resin matrix used inCFCC. The sag of ACFR is lesser than the ACSR from the installation temperature and up tomaximum operating temperature (after knee point the core will take the entire mechanicalload and thus the conductor mechanical characteristic behave similar to core after knee point).
The comparison of ACSR and ACFR conductor for a 132 kv transmission line is shown in theTable-II.
Table-II Comparison of ACSR and ACFR for 132 kv transmission line
PropertiesACSR Panther ACFR Himalaya
Construction (No./mm)
Conductor Diameter (mm)2121Core Diameter (mm)97.8
Cross sectional area (mm2)261
312Ultimate Tensile Load (kN)
89.7
95.3
Weight (kg/km)
974
820
DC Resistance at 20 oc (ohm/km)
0.13900.1018Current Carrying Capacity (Amperes) (Ambient 45oc)
Operating temperature – 75oC
366
464o
Operating temperature – 85 C
466
537
Operating temperature – 180oC-1061
Sag and Tension for 320-meter spanoTension at 32 C Full wind (52 kg/mm2) Kg
3324
2739
Sag at 75oC and Nil Wind
6.90
5.99o
Sag at 85 C and Nil Wind
7.09
6.39
Sag at 180oC and Nil Wind
6.66
3

The ACFR conductor is not only chosen for enhancing the power transfer capacity of theexiting transmission lines by replacing the existing ACSR conductor with ACFR conductor.
ACFR conductor has lesser AC resistance when compared to ACSR conductor, so it can be
deployed in new power transmission line to reduce the ohmic losses and thus reduce thecarbon foot print

4.

TESTINGIn the recent days CFCC and ACFR conductor has been tested for Design test, Installation test
and In-service test and the outcome of each test is discussed in detailed
4.1

STRESS STRAIN TEST

Stress Strain test on ACFR 315 mm2 was performed to room temperature and the data wascollected to support for the calculations of sag tension.
The procedure two stress strain tests were conducted, first test was conducted on ACFR
conductor and the other test was on the CFCC. Practically it is not possible to perform the teston the conductive layer annealed aluminium. So the stress strain characteristic of aluminiumis developed by subtraction CFCC core stress from the total ACFR conductor stress atcommon strain.
The results from the stress strain data were used to obtain the fourth quadrant polynomials
and are used to compute the sag tension results using PLS CADD software.
4.2

CREEP TESTThe creep test was performed holding the ACFR 315 mm2 at constant tension for 1000 hours.
To obtain a perfect fourth quadrant polynomial, the creep tests were performed at different
constant tension levels from 15% to 30% of RTS of the ACFR 315 mm2.
The strain due to creep will lead to increase in sag over a period of time, so the final sag needs
to be considered including creep strain.
It is observed from the test that ACFR conductor exhibits creep because of the conductive
layer and carbon composite core has almost zero creep. So the creep behaviour of aluminium
has been considered by the separation from the stress strain data.
4.3

SHEAVE TESTThe objective of the test is to observe the mechanical performance of ACFR 320 Sq.mm
conductor when subjected to simulated action of being pulled over a sheaves during
installation. This test is to show the conductor is robust for installation over stringing pulleys.
The ACFR 320 Sq.mm conductor was tensioned to 15% of the conductors RTS, the conductor
is passed 30 times over a pulley of diameter 20 times the diameter of the conductor, Aftercompletion of the sheave test the ACFR conductor was subjected to an ultimate tensile test.

4The ACFR conductor reached 128% of the conductor RTS as against the minimum
requirement of 95% of the conductor RTS. Furthermore the conductor doesn’t have any
broken strands or fretting on completion of the sheave test.
4.4

BENDING TEST ON CFCC

Bending test on CFCC diameter of 7.8 mm was performed to find the mechanicalperformance of the CFCC when subjected to combined bending and tensile stress.
CFCC sample was passed through the bending mandrel of diameter not higher than 50 timesof the core diameter and the sample was tensioned to 15% of the RTS of CFCC Core and kept
for one minute and 30% RTS of CFCC core for 2 minutes. The UTS test was performed after
bending test to find out the remaining tensile strength of CFCC, dye penetration test was also
performed to find any cracks on the CFCC sample
CFCC core attained 125% of the RTS of core against the requirement of 95% of the RTS ofthe core. In the die penetration, CFCC has not shown any kind of cracks or flaws.
4.5

HIGH TEMPERATURE TENSILE TEST ON CFCC

The purpose of the test is to measure the tensile stress of CFCC core at the short term
emergency operating temperature of 200oc.
The CFCC core was heated to 200oc, the sample was allowed to reach thermal equilibrium
before the tensile test, once the temperature is stabilised the CFCC was tensioned until failure
to determine its tensile strength.
The CFCC broke at 104% of the RTS of CFCC core against the requirement of 95% of theRTS of CFCC.
4.6

SALT SPRAY TESTACFR 320 Sq.mm conductor was performed for salt spray test to investigate the effect ofACFR conductor under a controlled salt atmosphere. The salt atmosphere is considered
typically the most corrosive environment the conductor will experience.
Samples of ACFR 320 Sq.mm were placed on the slat spray chamber the PH of the solution
was maintained between 6.68 to 7.04 at 25oc through out the test. The mass of the eachsample was measured prior to the test. The test was performed as per ASTM B117 for 1000
hours
The mass of each sample was measured after completion of the test and it was recorded tofind the loss of cross sectional area. After completion of test aluminium wires and CFCC were
tensile tested to find the loss of strength due to corrosive atmosphere.
There was no significant signs of pitting, corrosion or detoriation noted on aluminium wires
as well on CFCC

5

4.7

HEAT STRESS TEST ON CFCC

The CFCC core size of 7.8mm was performed for heat stress test to verify the mechanicalperformance of CFCC when exposed to combined mechanical and thermal stresses at its shortterm emergency operating temperature of 200oc.
CFCC core was heated to 200oc and allowed for thermal equilibrium, the tensile load of 25%of RTS of core was applied to CFCC core and held for 1000 hrs. After completion of 1000 hrs
the sample was tested for tensile load.
The CFCC attained 120% of RTS of core against the requirement of 95% of the RTS of thecore. No damage, cracks or breaks were observed on the CFCC sample.
4.8THERMAL AGING TEST ON CFCC

CFCC size of 7.8 mm was performed for thermal aging test to find the loss of strength of
CFCC while exposed to continuous operating temperature for long time.
CFCC sample was placed in the inside the tube furnace and temperature was raised to 180 oc
after attained the thermal equilibrium, the sample was exposed to 8736 hours (52 weeks). The
samples were collected at an interval of 400, 1500, 2500, 5000 and 8736 hours. Aftercompletion of 52 weeks the sample was tensile tested
CFCC tensile value achieved was 116% RTS as against the requirement of 95% of the RTS.
From the collected data and using logarithmic formula CFCC will degrade its UTS to 95% ofRTS after 15 million years of service

5.

TESTS AND RESULTS

ACFR Conductor and CFCC core samples were tested for all the needed relevant test as per
the test requirement specified in international standards and guidelines for High Temperature
Low Sag conductors the test results shows that the ACFR and CFCC core exceeds theexpectations of the acceptance criteria required for all the tests.
From the test results, ACFR conductor is proved to be robust in design, installation and inservice operation

6.

HARDWARE

The important hardware fitting is tension clamp and mid span joint, because for any
composite core overhead conductors the challenge is to hold the composite core. The
remaining other hardware and accessories can be designed considering other HALS typeconductor
6.1 TENSION CLAMP
The tension clamp of ACFR is same as ACSR conductor. ACFR tension clamps arecompression type as like ACSR. It has major three components composite core compression
6unit, Aluminium tube as a buffer and Outer aluminium compression unit. The aluminium
buffer is used to reduce the crushing of composite core during compression of the core potion.
Figure 2 and Figure 3 shows the components of tension clamp for ACSR and ACFR
conductor respectively
337mm
495mm
+1

Figure 2 ACSR Tension Clamp

Figure 3 ACFR Tension Clamp

The tension clamp of ACFR is little longer than the ACSR conductor which supports secured
current density and grip strength.
6.2 MIDSPAN COMPRESSION JOINT (MSCJ)
Figure 4 and Figure 5 shows the diagram and component of ACSR MSCJ and ACFR MSCJ
respectively

808mm
439mm

+4Figure 4 ACSR MSCJ

7.

Figure 5 ACFR MSCJINSTALLATIONACFR uses a stranded carbon fiber composite core CFCC, so ACFR conductor is moreflexible. Thanks to the flexibility of ACFR, the installation method of ACFR is similar toACSR. The tolls and tackles used for ACFR is same as that of ACSR. So the stringing
method as conventional as ACSR.
The Table – 3 shows the requirement for ACSR and ACFR during installation, It should be
noted that if ACFR uses outer conductive layer as annealed aluminium then the only
exception is recommended pulling angle is 60 degrees considering annealed aluminium may
get loose and bird cage may occur.

7Table 3 Installation Requirement for ACSR and ACFR
Description
Outer Conductive Layer
Bull Wheels
Sheave Wheels
Recommended pulling angle
Dead End Installation time
MSCJ Installation time

ACSR
HAL
40 X D20 x D
60 degrees
15 minutes
30 minutes

ACFR
Annealed AlTAL
40 X D
20 X D45 degrees
60 degrees
15 minutes
30 minutes

D – Diameter of Conductor

8.

Conclusion

ACFR conductor has the following advantages and the best choice for power transmission
overhead lines.
8.1
Stranded Carbon Fiber Composite Cable (CFCC) is having lesser weight. Highstrength and lower thermal expansion
8.2

CFCC is more flexible than the single carbon composite core

8.3
Aluminium Conductor Fiber Reinforce (ACFR) can be produced by any one ofthermal resistance alloy wire, annealed aluminium wire or hard drawn aluminium wire.
8.4
The outer conductive layer used in ACFR conductor can be produced by either roundwire or shaped wire depends on application need.
8.5ACFR is the best choice for reconductoring line to increase the transmission capacity
by more than 2 times of the existing capacity without any reinforcement of tower andmaintaining the same ground clearance
8.6
The new transmission line using ACFR will reduce the ohmic losses thus towards
green solution for energy delivery utilities
8.7
ACFR conductor has been tested for all the test requirements considering design,
installation and in-service operation
8.8

Test results exceeds the expectation and acceptance criteria specified for all the tests

8.9
The dead end clamp and midspan joint of ACFR conductor is same as that of ACSRconductor
8.10 Due to the more flexibility of ACFR conductor, the installation is same as that ofACSR conductor
8.11 Quicker installation and easy to handle than any other composite core conductor usedin power transmission line
End of text8

BIBLIOGRAPHY[1][2]

Working Group SC B2.26 CIGRE 426. “Guide for Qualifying High Temperature Conductors foruse on overhead Transmisison Line” (426 August 2010)
Working Group SC B2 Session paper “Development of a low sag aluminium conductor carbon
fiber reinforce for transmission line” (Reference Number 22-203_2002, Year 2002)

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