EuroWire November 2016

Technical article

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. 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. This model uses theoretical

8 wire sizes required using conventional system 2 wire sizes required using SIW system

▲ ▲ Figure 1

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.

In 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

▼ ▼ Figure 2: Strand simulator output 150mm 2 compact strand

▼ ▼ Figure 3

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) Outer gap area (mm 2 ) Insulation cos t (US$/km)

11.7

11.39 0.710

11.07 0.663

15.88

131.35

109.55

106.83

57

www.read-eurowire.com

November 2016