increasing lightning strength of optical ground conductors.pdf

TECHNICAL PAPER TP 2742

Increasing Lightning Strength of Optical Ground Conductors

Sedat Karabay

Received: 10 October 2012 / Accepted: 19 April 2013 / Published online: 28 August 2013

� Indian Institute of Metals 2013

Abstract In this article, testing and improvement stages

of AA6101 and 6201 materials used in manufacturing of

new generation optical ground conductors (OPGW)

installed against lightning strike have been presented. The

designed and manufactured prototype composite conductor

OPGW for Turkey’s transmission lines is composed of six

galvanized steel wires, one stainless steel tube with multi

glass fibers and 12 aluminium alloy wires. Test samples

prepared from prototype failed in first trial of lightning

strike due to spot melting of conductor outer surface. The

amplitude of the arc current was adjusted to 200A. The

duration of the arc was 500 ms with 100C total charge. It

caused breaking of excessive aluminium alloy wires at

outer layer. Thus material improvement by inoculation

with AlB2 compound into molten metal was applied at

continuous casting line. Its aim is to obviate destroying

effects of lightning strike by the increasing conductivity of

the base conductive part composed of alloy AA6101 and

6201 wires. Conductivity increases were made by trans-

forming detrimental transition impurities Ti, V, Cr and Zr

into diborides as TiB2, ZrB2, CrB2, and VB2. After all

OPGW composite conductor manufactured with improved

aluminium alloy wires passed lightning strike tests

perfectly.

Keywords Lightning strike � Conductivity improvement �AlB2 � AA6101 � Aluminium feedstock � Continue casting

1 Introduction

In this paper, the goal is to present engineering remedies to

pass the requirements of the lightning strike tests of the

product OPGW designed and manufactured for transmis-

sion lines of Turkey. The ground conductor is tested in the

laboratory by simulating atmospheric discharge conditions

to check the quality of the cables under those situations. On

the other hand, in the design stage, some theoretical studies

are performed by computational methods to simulate such

effects [1]. However, real conditions are completely dif-

ferent than theoretical studies. In a transmission line of

Turkey, several OPGW constructions are used, however

none of them is of domestic manufacture. For that aim,

Turkish Electrical Institution (TEI) decided to have a

versatile type OPGW which is compatible with all geo-

graphical conditions of the regions, and homemade product

in the country. By considering technical and economical

proposals of TEI, a new type optical ground conductor is

projected. It is composed of 1 stainless steel tube with

12–24 fibers and six extra high strength steel wires and 12

AlMgSi alloys wires especially AA6101 or 6201 stranded

at the outer layer. Afterwards, the manufactured prototypes

are exposed to several mechanical and electrical tests in the

laboratory before supplying it to field [2, 3]. The prototype

passed most of hard type-tests applied to product, however

it failed under ‘‘lightning strike’’ experiments. Most of its

aluminium wires were damaged due to melting by exces-

sive heat. To get rid of destroying effect of lightning

charge, it has been envisaged that main conductive part

should be improved to pass requirements of standard ‘‘IEC

60794–1–2; test procedure H2’’ and specification ‘‘H.KIB-

TEK/04-OPGW-TS-1 of TEI. Increasing of the diameter of

the conductive aluminium alloy wires is restricted by the

TEI due to sag tension incompatibility with the sag

S. Karabay (&)

Mechanical Engineering Department, Engineering Faculty,

Kocaeli University, Umuttepe Campus, Kocaeli, Turkey

e-mail: [email protected];

[email protected]

123

Trans Indian Inst Met (2014) 67(1):105–114

DOI 10.1007/s12666-013-0315-1

characteristic of existing earth wires [4, 5]. Moreover,

usage of new material alternatives such as Al clad steel

wire or Al clad steel tube is also limited owing to

increasing final product cost and investment budget.

Therefore the unique way for the solution of available

problem is to improve aluminium alloy when casting at

continuous casting line (CCL). Thus, improvement of the

conductivity of AA6101 and 6201 alloys has been planned

by inoculating AlB2 compound. Inoculation will be per-

formed in the tundish before pouring of molten aluminum

alloy into casting wheel to manufacture feedstock for

conductor production [6].

1.1 The Construction of Composite OPGW

A versatile loose buffer type OPGW has been designed

according to the specification ‘‘H.KIB-TEK/04-OPGW-

TS-1’’ prepared by TEI having regard to environmental

conditions of the country. And then the prototype OPGW

was manufactured in the plant. Cross sectional view and

properties of sub–parts are explained in Fig. 1a, b respec-

tively. In the design, the most important part is the con-

ductive section which is outer layer. It is composed of

aluminium alloy AA6101 or 6201 wires. Spectral analyses

of the conductive material used in the manufacture of the

OPGW conductor and its mechanical and electrical prop-

erties are indicated in Tables 1 and 2 respectively. To

begin with, the manufacturing of OPGW with conventional

AA6101 alloy was used. All physical parameters of alu-

minium wires with the nominal diameter of 3.05 mm

drawn from the conventional AA6101 feedstock are pre-

sented in Table 2.

1.2 Experimental Studies

Among of various tests applied to measure performance of

the new OPGW product, two tests are vitally important.

These are ‘‘short circuit’’ and ‘‘lightning tests’’. The con-

ductive material can be damaged in a few seconds when

exposed to short circuit and lightning effects [7]. The

prototype sample passed the short circuit test (Standard

IEC-60794-1-2-H1) perfectly. However, the same success

does not repeat in lightning tests, hence its outer layer

consisting of alloy AA6101 wires failed completely.

Damaging is related to its weak conductive ability against

applied excessive current shot. The external effect of

lightning strike causes generally spot melting on surfaces

of the conductor and breaking of wires. The prototype

OPGW sample was manufactured as 2 km at the plant and

supplied to the laboratory.

1.2.1 The Prototype OPGW Applied First Lightning Test

and Results

The first prototype of OPGW was manufactured using

conventional AA6101 with combination of elements

defined in the Table 1. In the construction described in the

Fig. 1a, b, the most important part is the outer layer. The

alloy was prepared in the holding furnace by adding AlSi

and Mg master alloys after filling the bath with 99.7 % EC

(Electrical conductor) grade pure aluminum. Then after

taking gas and dross of the bath, casting was performed

using crystallization wheel. The cast bar was manufactured

at 440 �C and then induction heating was applied to

increase temperature up to 540 �C. Afterwards it was fed to

rolling machine with 15 triple-strands to change trapezoi-

dal form into a circular cross section. At this moment in

line homogenization process is performed. Finally, the

manufacture of standard feedstock was completed by

prompt water cooling after the exit of the rod from the final

rolling strand. Subsequently, cooled feedstock in the final

pipe of CCL was drawn to required wire diameter and then

after artificial aging treatment (175 �C/6 h) they are

stranded as a composite structure with the planetary

stranding machine to obviate spring back of individual

wires. The test samples were cut from the manufactured

prototype. The samples with the length 50 m has been

clamped into the test stand as shown in Fig. 2. The OPGW

was prepared with a protective spiral and a guy spiral. With

a mechanical power drive in connection with a tension

meter, the OPGW tension was adjusted to 20 % of the

calculated breaking load (UTS) of the ground conductor

under test (17.9 kN).

For the purpose of mechanical damping during the

lightning test, two springs were installed at each end of the

mechanical system including the test object. The upper rod

Fig. 1 a Cross sectional view of OPGW. b Stranding view of

composite conductor OPGW. 1 aluminum wires, 2 steel wires, 3

stainless steel tube, 4 optical fibers

106 Trans Indian Inst Met (2014) 67(1):105–114

123

electrode is vertically adjustable and placed above the

OPGW. It is rounded at the end facing the arc and has a

diameter of 25 mm. With a wire (copper, diameter of

0.1 mm) lightning current is ignited [8, 9].

The ground wire under test was symmetrically con-

nected to the power source in order to minimize the mag-

netic force on the arc and to test under the hardest

condition five (5) tests were carried out on the test sample

at different places on the OPGW. The electrode gap was

adjusted to 80 mm and the cable was stressed with the

mechanical load of 20 % ultimate tensile strength (UTS)

[10, 11]. The amplitude of the arc current was adjusted to

200A. The duration of the arc was 500 ms with 100C total

charge according to international standard ‘‘IEC–60794-1-

2; test procedure H2’’ and specification ‘‘H.KIB-TEK/04–

OPGW-TS-1’’ of TEI. View of the conductive layer of

OPGW after application of lightning charge has been

presented in Fig. 3. A lightning strike is applied at different

places onto the conductor. Yet, each trial caused spot

melting of AA6101 alloy wires, hence excessive wire

breakage occurred at the outer layer. Broken wires at the

outer layers are 9–10 numbers. It means roughly that all

wires have been damaged because the external layer

involves totally 12 of AA6101 alloy wires.

1.3 Interpretation of First Lightning Test Results

After the application of first shot of lightning current, the

conductor must withstand 75 % of the rated tensile strength

(RTS). The RTS of the conductor is 8,950 kN. It means that

the broken wires at each trial are never more than nine wires

in the aspect of complete tensile strength according to tensile

load restriction of the standard ‘‘IEC-60794-1-2; test pro-

cedure H2’’ and TEI specification ‘‘H.KIB-TEK/04-OPGW-

TS-1’’. Moreover, it has been explained before that broken

wires of 9–10 numbers occurred in experiments were caused

by the lightning arc at each trial as indicated in Fig. 3.

Although considerably destroying of wires due to spot

melting, the conductor can still withstand 75 % of the RTS

due to higher breaking limit of extra high strength steel wires.

Any destroying effects on the surface of steel wires located

inner layer were not determined after several lightning shot

trials. Therefore, the problem is related to outer layer of the

Table 1 Spectral analysis of AA-6101 sample in %wt

Mg Si Fe Cu Zn B Cr V Ti

0.52 0.53 0.24 0.06 0.06 0.05 0.03 0.028 0.025

Table 2 Results for

conductivity and mechanical

parameters of the wires drawn

from conventional AA6101

alloy without inoculation with

AlB2 compound

The alloy wires on the spools

were exposed to artificial aging

(T-81) at furnace under

175 �C/6 h

Diameter

(mm)

Cross-

section

(mm2)

Resistivity

(ohm mm2/m)

DC resistance

at 20 �C ohm/km

Conductivity

(% IACS)

Breaking

load (N)

Tensile

strength

(N/mm2)

Elongation at

250 mm (%)

3.04 7.25 0.032610 4.498 52.8 2,305.31 317.97 4.6

3.04 7.25 0.032494 4.482 53.0 2,350.35 324.18 5.5

3.06 7.35 0.032854 4.470 52.4 2,390.60 325.25 5.4

3.05 7.30 0.032718 4.482 52.7 2,401.35 328.95 5.7

3.06 7.35 0.033038 4.495 52.1 2,412.26 328.19 6.1

Fig. 2 Schematic illustration of

lightning test stand

Trans Indian Inst Met (2014) 67(1):105–114 107

123

OPGW. The outer layer consists of 12 wires of AA6101

aluminium alloy. Apart from conductor withstand as 75 % of

the RTS after lightning shot, ‘‘H.KIB-TEK/04–OPGW-TS-

1’’ specification of TEI points out that complete conductor

resistance must not be increased 20 % after application of

lightning charge [11]. This rule restricts the maximum

number of broken wires in the OPGW conductor as three

wires [12, 13]. Thus, it is thought that as a remedy of solution

of the problem is to increase melting point of the material by

using some alloying additives into the molten material.

However, the material also should pass the minimum con-

ductivity level as 52.5 % IACS (international annealed

copper standard) required by the standards IEC-104 and EN-

50183. Thus, increasing melting point of the alloy with dif-

ferent alloying elements has been blocked by minimum

conductivity expectation from the conductive part. Another

possibility for elimination of the excessive broken wire

problem is to increase diameter of wires to transmit heat and

current from the lightning strike zone immediately. How-

ever, the diameter of the conductor is not increased due to sag

incompatibility with respect to the existing grounding wires

on the transmission lines. Because, increasing of wire

diameter results in increasing diameter of complete con-

ductor and causes incompatibility with tension equality

between trusses with others. Therefore, searching of material

improvement seems to be the unique way. Thus, improve-

ment of AA6101 and 6201 as base materials of the composite

structure was planned to pass the test requirements in the

project.

1.4 Modification of AA6101 and 6201 Alloys

by Inoculating with AlB2

The electrical conductivity of pure metals is reduced by the

presence of impurities and structural imperfections. It has a

great importance to minimize resistance losses in power

transmission applications by removing as many such

imperfections as possible. The rule of Nordheim states that

in the dilute case, the residual resistivity is proportional to

the impurity concentration. Table 3 shows the influences of

selected solutes on the electrical conductivity of

aluminium.

When present in a precipitated rather than solute form,

the impurities cause a much smaller reduction in conduc-

tivity. Thus, conductor producers have focused their

attentions on improving methods to use cheap and poor

materials (non EC (electrical conductor) grade) in their

processes. The electrical conductivity of aluminium is

impaired generally by the presence of heavy metal impu-

rities such as Ti, Cr, Zr and V in solid solution as indicated

in Table 3 [14, 15]. Master alloys containing AlB2 and

AlB12 compounds are successfully used to increase the

electrical conductivity of aluminium 99.6 and 99.7 % [16].

In the literature, the base study realized by means of

industrial applications for increasing conductivity is related

to measurement of secondary phases of the material sam-

ples as: I- 99.6 % poor Al (non EC grade) and the sample

II: perfect EC grade 99.7 % material and the sample-III:

99.6 % poor Al but inoculated with AlB2. Results were

outlined in final column of Tables 4 [16]. It has been

approved in the study presented in Table 4 that the poor EC

grade aluminium 99.6 % responded to inoculation with

AlB2 by increasing of total secondary phases (R%). Hence,

increasing of the conductivity of the alloy AA6101 is

realized. Detailed information about improvement can be

found in the references [16, 17]. Boride formation of the

transition elements after inoculation with AlB2 and AlB12

has been approved by several researchers [14–17]. When

boron is added to the melt, the most probable compounds

that can be formed are diborides such as TiB2, ZrB2, CrB2,

and VB2, which are insoluble boron compounds. Inocula-

tion of aluminium 99.6–99.7 % with sufficient AlB2 or

AlB12 results in instantaneous reaction, and borides are

quickly and completely precipitated [16, 17].

Fig. 3 Views of melted and broken wires on the conductor after

application of first lightning test

Table 3 Influences of solute impurities on electrical conductivity

[14, 15]

Element Max. solubility

in (Al. %)

Estimated average decrease in

% IACS per wt%

In solution Precipitated

Fe 0.052 29 1.2

Si 1.65 16 1.8

Ti 1.0 31 2.5

V 0.5 34 5.5

Cr 0.77 36 3.7

Zr 0.28 23 0.9


123

These insoluble borides have an insignificant detri-

mental effect on the conductivity. It is reported that AlB2

reacts with heavy metal impurities [14] to transform bo-

rides faster than AlB12 [15]. In addition, AlB2 forms

smaller transition diboride elements than AlB12, resulting

in a lower settling rate with a larger volume of small par-

ticles suspended in molten metal. Settling rates of diborides

precipitated with AlB2 take a longer time than AlB12 as

shown in Fig. 4 [15]. The insoluble boride particles formed

by reaction between impurities and the boron tend to settle

out of metal and thus provide no significant grain-refining

response. In particular, when there is an excess of B, an

effective grain refinement cannot be achieved. Figure 5

indicates the performance characteristics of AlB2 com-

pounds according to time and percentage of total Ti, Cr,

and V settled [15, 17].

Precipitation of transition elements from solution occurs

in 1 min, as evidenced by the rapid increase in the con-

ductivity. Settling continued to occur over a period of

several hours, however no additional increase in the con-

ductivity was observed. It is also reported that when

99.7 % of Al is inoculated with AlB2 compound over the

required quantity, it has no effect on increasing the con-

ductivity [15, 17].

The alloy AlB2 and AlB12 phases differ both in mor-

phology and particle size, with the AlB2 the phase having a

significantly smaller particle. Insoluble borides precipitated

using AlB2 are predominantly equiaxed and hexagonal in

geometry, with an occasional platelet [15, 17]. SEM views

of AlB2, AlB12 phases were showed in Fig. 6a, b respec-

tively [15]. AlB12 precipitates a coarser or more dense

particle than AlB2. In our experiments, each of the com-

pounds with different boride types indicated in Fig. 6a, b

was tested in the continue casting process when casting of

the molten conductive metal. Predominant boride phase

AlB12 has considerably sticky properties. It caused clog-

ging of the float valves in the tundish. Thus, continuous

flowing of the metal to solidification wheel was blocked,

process was stopped several times. In contrast to that, the

compound with predominant boride phase AlB2 fed into

molten metal in the tundish was used without any problem

when metal passed between float–valves. Thus, in the

practical applications, smaller boride size AlB2 phase seen

in Fig. 6a can be used in CCL perfectly without reasoning

any problem. Experimental study related to conductivity

improvement for AA6101 and 6201 with AlB2 was per-

formed with type Z1800?ZZS255/15 (made by China)

continuous casting and rolling machine designed for pro-

duction of AlMgSi alloys. In manufacturing of OPGW,

stages of melting and casting, inoculation with AlB2

compound, forming of feedstock and artificial aging are

Table 4 Inoculation of poor

grade 99.6 %Al with AlB2 and

occurrence of secondary phases

Sample code no Blocky primer phases Eutectic

Primer phases

R%

secondary

phasesWhite contrast

contrast

Grey contrast

I–99.6 % Al and non EC grade 0.06 ± 0.116,

Ca–Al–O–P

?Ca–Al–O–P 0.34 ± 0.204

FeAl3

0.40

II–99.7 %Al EC grade – 0.29 ± 0.314, Si 0.67 ± 0.456

FeAl3

0.96

III–99.6 % Al non EC grade but

inoculated with AlB2

– 0.17 ± 0.246

Ca–K–Al–O

0.60 ± 0.211

FeAl3

0.77

Fig. 4 Settling rates of AlB2 and AlB12 compounds

Fig. 5 Performance characteristics of AlB2


123

presented in Fig. 7. Material crystallization wheel diameter

is 1800 mm and the final feedstock diameter is 9.5 mm.

Rolling type is 15 Y-type 3 rollers. Its production capacity

is between of 4.2–6 t/h. To begin with the alloy AA6101

was prepared in the holding furnace and casting was per-

formed. Then same procedure was followed for AA6201.

Alloy AA6201 is a higher strength material than AA6101.

Each of two can be used in manufacturing of AAAC (All

Fig. 6 SEM view of a AlB2

phase, b AlB12 phase

Fig. 7 Flow chart of the

aluminium conductor

manufacturing process and

inoculation with AlB2


123

aluminium alloy conductors, AAAC) and OPGW.

Increasing strength adversely affects conductivity of the

material due to alloying elements. Therefore, AA6101 was

preferred as favourite conductive material of the OPGW

product. Each material was experienced to increase con-

ductivity because if any problem related to the strength of

the product is faced, an alternative material AA6201 will

be considered immediately instead of AA6101. Main

alloying elements of the AA6101 and AA6201 materials

were arranged as 0.52 % Mg, 0.53 % Si and 0.57 % Mg,

0.57 %Si respectively. In the experiments, each casting

was inoculated with 3 % AlB2 compound separately when

flowing as melt to solidification wheel. Material tempera-

ture in the tundish is around 730–750 �C. The feeding of

3 % AlB2 compound with special unit into tundish was

performed under the speed of 3 kg per ton cast alloy.

Narrowed channel section in the tundish increases the

speed of melt and causes easy mixing of master alloy for

satisfactory inoculation. The temperature of the cast bar

was kept in 420–440 �C after crystallization wheel.

Excessive cooling of the trapezoidal bar lower than 440 �C

is obviated by decreasing mass flow rate of water spray.

This is absolutely required to increase the temperature for

in-line homogenization. The rolling line has an induction

heater for increasing temperature as ?100 �C. After

application of the straightening to the bar, its temperature

Fig. 8 Changing of temperature of T-81 artificial aging versus to

conductivity and tensile stress for the alloy AA6101

Table 5 Results for

conductivity and mechanical

parameters of the wires drawn

from AA-6101 AlMgSi alloy

after inoculation with 3 % AlB2

Materials were exposed to

artificial aging treatment (T-81)

at 175 �C/6 h

Diameter

(mm)

Cross-

section

(mm2)

Resistivity

(ohm mm2/m)

DC resistance

at 20 �C ohm/

km

Conductivity

(% IACS)

Breaking

load (N)

Tensile

strength

(N/mm2)

Elongation at

250 mm (%)

3.04 7.25 0.030254 4.173 57.0 2,406.46 331.92 6.3

3.04 7.25 0.030218 4.165 57.1 2,434.90 335.84 6.7

3.06 7.35 0.030262 4.116 57.0 2,409.44 327.81 7.0

3.05 7.30 0.030201 4.129 57.2 2,415.25 330.85 7.2

3.06 7.35 0.030175 4.094 57.3 2,425.12 329.94 7.4

Table 6 Results of wires drawn

from 6201feedstock without

inoculation AlB2 and treatment

of artificial aging

Diameter

(mm)

Cross-

section

(mm2)

Resistivity

(ohm mm2/m)

DC resistance

at 20 �C ohm/

km

Conductivity

(% IACS)

Breaking

load (N)

Tensile

strength

(N/mm2)

Elongation

at 250 mm

(%)

2.5 4.91 0.035343 7.20 48.7 1,300 264.8 3.9

3.0 7.07 0.035272 4.99 48.9 1,850 261.7 4.3

3.5 9.62 0.035117 3.65 49.1 2,465 256.2 4.0

4.0 12.57 0.035312 2.81 48.8 3,200 254.6 4.1

4.5 15.90 0.035149 2.21 49.1 3,985 250.6 4.1

Table 7 Results of wires drawn

from inoculated with 3 % AlB2

6201feedstock after artificial

aging (T-81) at 175 �C/6 h

Diameter

(mm)

Cross-

section

(mm2)

Resistivity

(ohm mm2/m)

DC resistance

at 20 �C ohm/

km

Conductivity

(% IACS)

Breaking

load (N)

Tensile

strength

(N/mm2)

Elongation

at 250 mm

(%)

2.5 4.91 0.031031 6.32 55.57 1,480 301.5 4.3

3.0 7.07 0.031102 4.40 55.44 2,120 299.9 4.5

3.5 9.62 0.031269 3.25 55.15 2,850 296.2 4.3

4.0 12.57 0.031165 2.48 55.33 3,750 298.4 4.4

4.5 15.90 0.031173 1.96 55.32 4,720 296.8 4.6


123

was increased up to 540 �C when passing across the tunnel

of induction heater. Then it is rolled with 15Y-3 rollers up

to decreasing 9.5 mm standard diameter. After a final

roller, prompt cooling with water which has a temperature

of 20 �C is applied to decrease temperature of rod imme-

diately below re-crystallization temperature. This applica-

tion prevents occurring of uncontrolled clustering of Mg2Si

hard particles.

After have completed casting on each of AlMgSi alloys

as 9.5 mm feedstock, wire drawing process is applied.

Then, artificial aging treatment (T-81) is applied to the

wires at 175 �C/6 h. This procedure is applied to each alloy

separately.

1.5 Improving Results and Discussions

After improving of the AA6101 alloy at CCL, mechanical

and electrical parameters of the wires drawn from the

improved feedstock were presented in Table 5. According

to the conductivity level given in Table 5, AA6101 wires

reached EHC (extra high conductive) grade defined in

standard EN-50183. In other words, Table 5 shows

improving electrical parameters of the AlMgSi alloy after

inoculation with 3 % AlB2. Here, we are interested only in

increases of material conductivity, because it is very

important in betterment of current carrying capacity and

heat transfer of the conductive component of overhead

ground conductor OPGW.

Increasing percentages of the conductivities for

AA6101 and AA6201 are around 7.71, 5.54 % IACS

respectively. Tables 6 and 7 indicate mechanical and

electrical properties of data collected from the inoculated

6201 alloy before and after T-81 artificial aging. Figure 8

Fig. 9 a Optical view of the AA6101 metal matrix after inoculation

with AlB2, 175 �C\6 h and artificial aging. Distribution of the hard

particles Mg2Si are observed as dark violet due to applied etchant.

b SEM View of AA6101 structure after artificial aging and . c SEM

View of AA6101 structure after modification with AlB2. Material

matrix was exposed to T-81 artificial aging at 175 �C/6 h. EDX

analysis on the particles uniformly distributed in the matrix is also

presented. (Color figure online)

Table 8 Measured parameters of the second trial of lighting tests

applied to improved conductor

Test 1 Test 2 Test 3 Test 4 Test 5

U (V) 1,040 1,050 1,045 1,043 1,049

I (A) 175 222 215.3 220.4 225.7

Q (C) 87.18 111.06 107.34 109.73 112.75

t (ms) 498.2 500.3 498.6 497.9 499.6

I2t (KA2s) 15.25 24.65 23.11 24.18 25.44

Temp. (�C) 17.3 16.9 17.4 17.2 16.4

Melted wires outer

layer

1 2 1 1 2

Broken wires outer

layer

2 2 1 1 2

Melted wires inner

layer

0 0 0 0 0

Visible damage of

the optical unit

No No No No No

Remaining UTS 97.56 % 95.12 % 97.56 % 97.56 96.13 %

Electrical resistance

change

16.42 % 16.57 % 8.35 % 8.35 % 16.57 %


123

shows applied parameters (UTS, %IACS, �C) on treat-

ment and improvement of the conductivity of the

AA6101 alloy [18].

Figure 9 illustrates Mg2Si particle distribution which is

very effective only in increasing of strength of the alloy.

Samples were analyzed by optical microscope to see distri-

bution of the hard particles after modification of AA6101 and

AA6201 alloys with AlB2 compound. This analysis was

performed to detect any abnormal occurrence and whether

there is any inhomogeneity distribution of Mg2Si particles

after artificial aging treatment. Presentation of hard particles

distribution of compound Mg2Si is not related to the con-

ductivity increasing of the AA6101 and AA6201 alloys.

However in manufacturing of the optical ground wire,

minimum expectations of the standards related to tensile

stress and conductivity should be satisfied simultaneously as

described in the IEC-104. It is also known that increasing of

conductivity for the conductor alloys AA6101 and AA6201

can also be achieved by overaging. However, this application

causes loss of gained strength of the material. Inoculation of

AlB2 compound to the AA6101, AA6201 alloys leads to

increasing of conductivity by obviating loss of gained

mechanical properties after T-81 artificial aging.

Detection of the Mg2Si in the matrix of AA6101 alloy

with optical microscope was performed using etchant

prepared as; 90 ml distilled water, 4 ml HF, 4 ml H2SO4

and 2g CrO3. Exposing time of etchant to metal surface is

30 s. Etchant applied to material Al–Mg–Si indicates

Mg2Si as dark violet. After have completed availability of

uniform distribution of Mg2Si in the metal matrix, SEM

analysis indicated in Fig. 9b supported with EDX was

executed to approve the distribution of strengthening pha-

ses in conventional form in the matrix after inoculation of

metal with AlB2.

1.6 Second Trial of Lightning Test and Results

After have completed manufacturing of the OPGW with new

improved wires, samples were prepared for lighting tests

again. The test procedure has been applied as mentioned

above. The test was performed five times and results were

tabulated in Table 8. View of samples after application of

lightning charge to the OPGW has been given in Fig. 10a, b

1.6.1 Discussion in Second Trial of Lightning Test

performed with Modified AA6101

As seen in the Fig. 10a, b and Table 8 broken wires due to

melting of the lightning effect have decreased sharply as

number of 1 or 2. The main reason of decreasing numbers of

damaged wires is due to the high conductivity of the modified

wires compared to unmodified aluminium alloy AA6101. As

matter of course some damage related to individual wires on

the outer layer of the conductor occurred during test trials.

However, the numbers of the broken wires in the second

lightning test are very low when compared to that of first

lightning tests. Hence, it satisfied both strength restriction

75 % RTS and restriction related to resistance increases of

the initial resistivity of the conductor as 20 % which permits

maximum three wires broken after lightning charge

according to specification‘‘H.KIB-TEK/04–OPGW-TS-1’’

of TEI.

2 Conclusions

Conductivity improvement of the AA6101 and 6201 alloys

with minor concentration of transition elements is per-

formed at aluminium continue casting line using AlB2

Fig. 10 a, b Views of conductor lightning arc current applied to improved conductor and surface of OPGW after second trial of lightning test

respectively


123

compound. Feeding rate of AlB2 compound as rod form

with 9.5 mm diameter is arranged as 3 kg/ton into molten

metal when flowing in the tundish located between holding

furnace and solidification wheel. In the study, inoculation

of the molten aluminum alloys with AlB2 does not show

any detrimental effects on tensile strength and elongation

properties of the wire products after artificial aging treat-

ment at 175 �C/6 h. Thus, keeping mechanical properties

constant, electrical properties of the alloy AA6101 are

improved. Ultimately, OPGW composite conductor man-

ufactured with increased conductivity wires passed light-

ning test perfectly by satisfying international standard and

national specification requirements. The OPGW presented

in the article has been used successfully in transmission

lines of Turkey.

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http://www.teias.gov.tr

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