59 / 88
Technical article
November 2016
57
www.read-eurowire.comIn a similar way, 35mm
2
to 500mm
2
the
number of wires can be reduced from 12
to three. This reduction in the required
number of wire sizes brings about major
cost savings in the wire drawing area:
• Creates a higher productivity in the
wire drawing machine due to the
elimination of multiple set-ups for the
different wire diameters required for
the traditional strand designs
• Reduces the amount drawn wire scrap
through wire size changeover
• Creates a reduction in the wire
drawing die inventory
Similarly the roll forming process has
a cost saving impact in the stranding
process:
• Lower volume of different wire sizes
being produced to await the stranding
process
• Ability to use larger package sizes and
switch from a bobbin system to a stem
pack system
• A reduction in down time due to
loading, with the ability of automatic
pay-off changeover while the machine
is running
• Quicker set-ups for different strand
sizes due to the elimination of the
movement of different pay-off sizes
• Higher linear production speeds, when
compared to conventional stranding
methods
• Reduction in manning levels in the
stranding process
Material Savings
The challenge for today's manufacturers is
to determine what target is to be chosen
within the scope of the specifications.
If the criteria for determining the
construction were based solely on the
economics, the industry would gravitate
to the unilay conductor schedule, and the
smallest diameter that is allowed within
that schedule. The roll form process allows
unilay products produced up to 500mm
2
.
Statistical analysis of strands compacted
with methods (die or rollers) other than
the roll form system has shown that
a typical material variance of ±1% to
±1.5% must be expected. These results,
therefore, lead to the need to oversize the
conductors by at least three per cent in
order to ensure that product does not fall
below specification. This excess material
is, effectively, given to customers free of
charge.
When utilising the Ceeco Bartell roll form
system with its strand design software, the
material variance is reduced dramatically.
Giving a real and very tangible material
saving over conventional compacting
methods, this is particularly important
with the current cost of aluminium and
copper.
This means that the minimum diameters
specified in the IEC and ASTM standards
can be achieved, while at the same time
approaching but not exceeding the
maximum resistance.
Due to the wide variety of strand that is
used in the industry, Ceeco Bartell has
developed a mathematical model to assist
with the strand design.
This
model
uses
theoretical
and
quantitative data that allows prediction of
the resistance of the strand. This program
further analyses the geometry of the
strand to optimise the performance of
the machine. The result is an accurate
prediction
of
the
finished
strand
resistance.
Figure 2
shows a cross section of a 150mm
2
strand, showing how this program assists
in the development of the optimum strand
design.
This roll form programme provides the
greatest potential as it has the smallest
strand diameter schedule for a specific
stand size. Consequently this also
represents the greatest potential for
insulation savings for a given insulation
thickness.
This can be clearly seen in
Figure 3,
which shows savings in insulation while
producing 95mm
2
XLPE product with fill
factors ranging from 86 per cent to 96 per
cent. As the conductor becomes smaller
and the interstices disappear, the amount
of insulation used will be reduced.
▲
▲
Figure 1
8 wire sizes required using conventional system
2 wire sizes required using SIW system
▼
▼
Figure 2:
Strand simulator output 150mm
2
compact strand
Economic analysis of 95mm
2
XLPE product
Fill factor
86%
92%
96%
Configuration
1=6=13
1=6=11
2=6=9
Outer diameter
(mm)
11.7
11.39
11.07
Outer gap area
(mm
2
)
15.88
0.710
0.663
Insulation cos
t (US$/km)
131.35
109.55
106.83
▼
▼
Figure 3