increasing lightning strength of optical ground conductors.pdf
DESCRIPTION
by juanTRANSCRIPT
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];
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
108 Trans Indian Inst Met (2014) 67(1):105–114
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
Trans Indian Inst Met (2014) 67(1):105–114 109
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
110 Trans Indian Inst Met (2014) 67(1):105–114
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
Trans Indian Inst Met (2014) 67(1):105–114 111
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 %
112 Trans Indian Inst Met (2014) 67(1):105–114
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
Trans Indian Inst Met (2014) 67(1):105–114 113
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.
References
1. Gomes K D C, Martins T C, Dmitriev V A, Pinho J T, Colle S,
Andrade M A, da Silva J C V, Bedia M, in Proceeding the 59th
International Wire & Cable Symposium IWCS/IICIT, (2010),
p 199.
2. Alvim M G, in Proceeding 40th Session of CIGRE,B2-316 Aug.
29–Sept. 03, Paris, (2004), p 1.
3. Martınez J A, Castro F, Ingeniare. Rev. Chil. Ing 18 (2010) 120.
4. Li J, Sun D D, in Proceeding International Conference on
Industrial and Information Systems, (2009), p 39.
5. Yokoya M, Katsuragi Y, Nagata Y, Asano Y, IEEE Trans Power
Deliv, 9 (1994) 1517.
6. Criasafulli C A, Spoor D J, in Australasian Universities Power
Engineering Conference P–106, (2008), p 1.
7. Goda Y, Shigenu Y, Watanabe S, IEEE Trans Power Deliv 19(2004), p 1734.
8. Martinez JA, IEEE Trans Power Deliv 20 (2005) 2200.
9. Jakl F, Jakl A, IEEE Trans Power Deliv 15 (2000) 278.
10. Torvath T, J Electrost 60 (2004) 265.
11. www.teias.gov.tr, H.KIB-TEK/04–OPGW-TS-1, (2013), p 1.
12. Chrisholm W A, Levine J P, Chowdhuri P, in Proceeding of
Power Engineering Society, 1, (2001) p 88.
13. Iwata M, Ohtaka T, Kuzuma Y, Goda Y, International Confer-
ence, (2012), p 1.
14. Cooper P S, Kearns M A, The 5th International Conference on
Aluminum Alloys, July 1–5 Grenoble, (1996), p 1.
15. Setzer W C, Boone G W, Light Metals (1992) 837.
16. Karabay S, Uzman I, J Mater Process Technol 160 (2005) 174.
17. Karabay S, Uzman I, Mater Manuf Process 20 (2005) 231.
18. Karabay S, Mater Design 27 (2006) 821.
114 Trans Indian Inst Met (2014) 67(1):105–114
123