CIGRE-IEC 2019 Conference
on EHV and UHV (AC & DC)
April 23-26, 2019
Hakodate, Hokkaido, Japan21, rue d’Artois, F-75008 PARIS
http : //www.cigre.org

Type here the Study Committee or Technical Committee
High corrosion resistance of ACFR conductor

Y. KONDOTokyo Rope International Inc.
Japan

SUMMARY
Regarding new overhead conductor cable technology called as “Carbon Fiber Composite
Core conductor”, the technology shows great interest in its superior characteristics increasing
the capacity, low sagging and low losses without doing any changes in existing tower
structure modifications.
But the product life time with respect to corrosion aspect is also an important factor to beconsidered. This paper brief about the corrosion aspect of ACFR (Aluminum Conductor FiberReinforced) conductor which use Carbon Fiber Composite Cable (hereinafter, called CFCC)
as core.
Tokyo Rope International Inc. (TRI) performed a salt spray test for evaluating the corrosion
resistance of the ACFR compare to the ACSR. As a result, almost no corrosion occurred in
the ACFR with compare to ACSR in which the steel core and the aluminum conductor causedcorrosion. It was confirmed that the ACFR has better corrosion resistance compare to theACSR.

KEYWORDSHTLS Conductor, Carbon fiber composite core, ACFR, Reconductoring transmission line, Carbon
composite core conductor, Corrosion, dissimilar metal, Galvanic corrosion, Bimetal corrosion

Kondou.yasuyuki@tokyorope.jp

1. Introduction
In recent years, due to its excellent properties, using carbon fiber as a core material is more
popular and it is preferable choice for global power transmission utility. There are several
overhead conductor cable manufacturers who use different types of carbon fiber composite asa core of conductor cable. Especially, these are being introduced to the market where power
demand is vigorous.
Product service life of conductor cable may exceed 40 years. One of important factor that
determines the product life of conductor cable is “corrosion”. ACSR consists of steel core andaluminum where both materials are not having same potential differences. Corrosion often
becomes a serious problem depending on the use environment. It is very important to evaluatethat conductor cable using carbon fiber core has sufficient corrosion resistance performanceeven when compared with ACSR.

2. Characteristics of ACFR
Aluminum Conductor Fiber Reinforced (hereinafter, this is called “ACFR”) conductor
construction is as simple as ACSR conductor where the stranded steel core is replaced withstranded carbon fiber composite core. The trapezoidal wire shaped construction of ACFR
conductor is shown in Figure-1.
The raw material carbon fiber and epoxy resin matrix are bunched together to form acomposite wire and are coated with protection layer. And thus formed single carbon fiber
composite wires are stranded together to form a stranded Carbon Fiber Composite Cable(hereinafter, this is called “CFCC”). CFCC has the same advantage as that of the single
carbon fiber composite core like higher strength, lower weight, lower thermal expansion andhigher corrosion resistance.

ACFRACSR

Figure-1 The trapezoidal wire shaped construction of ACFR and ACSR

3. Mechanism of corrosion
There are several mechanisms of corrosion. Here lists the major ones.
(1) Galvanic corrosion (Figure-2, aka. Bimetallic corrosion)
When two metals with different electrode potentials (ex. aluminum and steel) contacts
each other in the presence of an electrolytic solution (ex. salt water), the less noble metal
corrodes faster.
This corrosion shall occur when both of the following two conditions are met.:(i) the dissimilar metals come in contact with each other electrically,(ii) both metals are immersed in one electrolytic solution.

1

Figure-2 Galvanic corrosion(2) Pitting corrosion (Figure-3)
Normally aluminum exposed to the atmosphere has a thin oxide skin on its surface, which protects
the metal from further oxidation. When the skin is destroyed by attacks of chloride ions (Cl-),
corrosion starts at that specific point. Theoretically this type of corrosion has nothing to do withother materials, and sometimes results in pits extending from the surface into the metal.

Figure-3 Pitting corrosion(3) Crevice corrosion (Figure-4)

When aluminum has some deposits on its surface, then the deposits makes a narrowspaces (this is called “crevice”) which the access of the working fluid from theenvironment is limited. When the inside and outside of that crevice have different oxygen
concentrations, aluminum inside the crevice corrodes faster due to the formation of an
oxygen concentration cell.

Figure-4 Crevice corrosion

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4. Progressive behavior of corrosion
The environmental factors related to corrosion of overhead transmission lines are almost
caused by sea salt. In the survey results in Japan, data showing that sea salt corrosion has
occurred is 74%. [1]Sea salt corrosion mechanism is based on galvanic type corrosion and this ischaracterized mainly in inner aluminum wire layer of overhead conductor.
, based on galvanic corrosion, is characterized by corrosion progress of aluminum conductor
mainly inside the electric wire (shown in Figure-5 [2] ).

Figure-5 ACSR sample from coastal area of Japan [2]In ACSR, it is known that galvanic corrosion occurs at
the interface between steel core and Aluminumlayers/strands during its service life. Similarly, galvanic
corrosion occurs between carbon fiber and aluminumlayers/strands if carbon fiber and aluminum are contacted
directly in the presence of an electrolytic solution.
In ACFR, a protection layer impregnated with epoxy
resin is wrapped around the each strand of the carbon
fiber composite material (Figure-6). The protection layer
prevents direct contact between carbon fiber andaluminum layer of ACFR.

Figure-6 Protection layer of CFCC

Among these corrosion mechanisms, it is difficult to estimate which mechanism will bedominant for overall corrosion. For this reason, a salt spray test, which is expected toreproduce the actual corrosive conditions in practical use, was conducted to compare thecorrosion characteristics of ACFR and ACSR.

5. Appearance evaluation in salt spray test
In order to accelerate evaluation of the occurrence of corrosion, salt spray test was applied.
The testing conditions are as shown in Table-1.
Due to period of time duration, 1,000 hours is the longest “recommended periods ofexposure” in ISO 9227:2012. 2,000 hours in which salt spray test was carried out was twice
the longest time 1,000 hours in ISO, and this was used as a breakpoint for our evaluation.
Conductor specimens were shown in Table-2. All the conductors were subjected to a salt
spray test with the outer layer of the aluminum conductor stripped in order to make significant
difference in a short testing time.
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Table-1 Testing condition of salt spray test
Description

Value

Testing standard

ISO 9227:2012(This is equivalent to ASTM B117-16 and JIS Z 2371.)

Test solution

50 g/L sodium chloride (pH 7.0)

Period of time duration

1,000hr, 2,000hr

Testing apparatus

Salt splay testing machine at Tokyo Rope laboratory(Picture shown in Figure-7)(i) ACFR and (ii) ACSR are simple relative
comparisons.
(iii) The study was also carried out with two
conditions of ACFR that is one sample “with”
protection layer CFCC core and the other“without” protection layer CFCC core.
Figure 7 - The overview of apparatus setup
Table 2 - Testing condition of salt spray test
Description

UnitWholeconductor-Tested condition-Value(i) ACFR 315(ii) ACSR 410(iii) ACFR 315

Round shaped
aluminum wire, Zinccoated steel core
The amount of Zinc
coating: 260 g/m2 ormore (JEC-34042010).

Trapezoidal shaped
aluminum wire,
CFCC core“without”
protection layer

Detail-Trapezoidal shaped
aluminum wire,
CFCC core “with”
protection layerCore sizeNos./mm

7 / 2.6

7 / 3.5

7 / 2.6Aluminum
conductor sizeNos./mm

6 / 4.98(Outer 10 / 4.98)

10 / 4.5(Outer 16 / 4.5)

6/4.98(Outer 10 / 4.98)

Outer diameter

mm

22.36

28.5

22.36

4

6. Result of appearance evaluation in salt spray test(i)ACFR (core “with” protection layer): After completion of 2,000 hours test, the innersurface of the aluminum conductor was a shiny and with good surface condition by seeing
with naked eye. And there was no indication that galvanic corrosion occurred.
(ii) ACSR (Zinc coated steel core): After completion of 2,000 hours test, the inner surface of
the aluminum conductor was not shiny when compared with the sample before salt spray test.
And Aluminum hydrate adhered on its surface. It was observed that small red rust in the steel
core even with the presence of Zinc coating, it was understood that steel and aluminum bothwere contacted each other and galvanic corrosion has occurred.
From the above, in the ACFR, protection layer hardly prevents progress of galvanic corrosion
by avoiding direct contact between CFCC core and aluminum conductor. Moreover, corrosion
resistance performance of ACFR is considered that it might be better than ACSR whichcannot avoid contact with dissimilar metals corrosion.
(ⅲ) ACFR (core “without” protection layer) : After completion of 2,000 hours test, although
the shine on the inner surface of the aluminum conductor is partly lost, the surface condition
is good and there are no signs of corrosion due to dissimilar metals is occurring.
The ACFR without protection layer, it was observed that the carbon fiber is exposed on thesurface, but its surface area is very smaller than the area of the aluminum conductor. Thecontact of carbon fiber and aluminum conductor may initiate the galvanic corrosion, but its
corrosion rate is slow compared to the corrosion rate of ACSR.

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Table-3 Appearance comparison in salt spray test
Initial state
0 hourSalt spray
1,000 hours e xposure

Salt spray
2,000 hours e xposure

Aluminum
conductorr
CFCC core(iii) ACFR
without protection layer

Steel core(ii) ACSR

Aluminum
conductor

CFCC core(i) ACFR

Aluminum
conductor

Spe cime ns6

7. Salt spray test by Kinectrics
The results of salt spray test that was conducted by Kinectrics Canada are shown in thissection. The condition was based on ASTM B 117 and test date: June, 2018 – August, 2018.
550 mm2 ACFR / TW (Core designation: 7 / 3.2, 9.6 mm CFCC) was used for evaluation.
The objective of the salt spray test is to investigate the effects of a controlled salt spray
exposure on samples of 550 mm² ACFR/TW conductor for 1,000 hours. After completion of
1,000 hours of test, tensile strength test for Aluminum wire and CFCC core was performed.
All three (3) samples were simultaneously subjected to salt spray exposure in anenvironmental chamber operated for 1000 hours (Before salt spray test, shown in Figure 8).

Figure-8 550 mm² ACFR/TW Conductor specimens of salt splay test

The condition of the samples after the salt-spray exposure is shown in Figure 9. Minor
discoloration of the aluminum wires was noted after 1,000 hours salt spray exposure samples.
Overall there were no significant signs of pitting, corrosion or deterioration noted on any
component of the conductor after the 1,000 hours salt-spray exposure.

Figure-9 550 mm² ACFR/TW Conductor specimens of salt splay test

Material property test results after 1,000 hour salt spray exposure are shown in Table 4.
The measured tensile strength of the CFCC core is 119.8% RTS and aluminum wires are
117% RTS after completing the 1,000 hour salt spray exposure (Table-4).
The sample of 550 mm² ACFR/TW conductor including 7/3.2, 9.6 mm CFCC core, as tested,
met the requirements for the salt spray test as defined in Cigre Technical Brochure TB 426“Guide for qualifying high temperature conductors for use on overhead transmission lines”.

Table-4 Tensile strength test results after salt spray exposure

78. Conclusion
 Regarding ACFR, since the CFCC core is covered with protection layer, the progress ofgalvanic corrosion is much slower than ACSR. And ACFR has excellent corrosion
resistance performance.
 It was confirmed that there was no change in mechanical properties in the 1,000 hour salt
spray test conducted in Kinectrics in accordance with Cigre Technical Brochure TB 426.

BIBLIOGRAPHY[1] The Institute of Electrical Engineers of Japan, Technical report No.968, Page5-6, June
2004[2] I. Ito et al. “Corrosion Characteristics on an Investigation of Sampled OHTL Conductors
and a Probabilistic Lifetime Estimation Method” CIGRE B2_213_201289