EoW November 2009

Power cables

Low friction cable jacketing Medium to high voltage power cables are used for a wide variety of applications, many of which place significant stresses upon the cable. This is particularly the case where flexibility combined with excellent mechanical and chemical resistance is a core requirement, such as cable carrier systems. Constant movement of the cables wears down the protective coating, leading to greater cost being incurred through replacement and any associated downtime. TPU is a high performance material that provides very low abrasion loss, making it an ideal option for jacketing of power cabling applications where endurance is a core quality.

XLPE insulated power cable

Polymers devoted to XLPE insulation compounds are essentially low-density polyethylene with a melt index of 2 to 3 crosslinked with the appropriate pero- xide. Dicumyl peroxide, such as Arkema’s Luperox ® DC is the most common peroxide used to crosslink insulation. The peroxide crosslinking mechanisms in polyethylene start with a unimolecular thermal decomposition of dicumyl pero- xide that forms cumyloxy radicals. These radicals may then abstract hydrogen from the backbone of a polymer chain to give cumyl alcohol or undergo β-scission to form acetophenone and methyl radicals. Two carbon radicals in two separate polymer backbones then combine to form a crosslink. Higher crosslinking levels can be achieved using Luperox F because of its higher active oxygen content. For direct peroxide injection processes (DPIP), the preferred liquid peroxide is tert butyl cumyl peroxide, such as Luperox 801. Arkema’s peroxides are used across the whole family of crosslinkable insulation, from low to extra high voltage. Under the combined effect of a con- taminant, the presence of water, and an electrical field, a bow tie tree shape can develop inside the insulation, weakening the dielectric properties. Tree length and tree density are detrimental to the cable life. Adding ethylene-acrylate copolymers to LDPEs imparts exceptional resistance to water tree formation in the compound. Incorporating 10-15% of Lotryl methyl or butyl acrylate copolymers can reduce the occurrence of water treeing by 75%.

Huntsman’s TPU offers a wide range of key properties, making it a highly versatile and effective material for the protec- tion of cables, including medium-to-high voltage power cables. The growth of auto- mation over the last ten years has led to the inclusion of control cables with those providing power. This bundling has led to a further key consideration, which is movement and flexibility over a broad temperature range from -40°C up to +140°C. Utilising Huntsman’s TPUs, such as Irogran ® A85P4380, cable producers are able to produce low friction cable jacketing. The characteristics of these special TPU grades mean that they can combine excellent abrasion resistance with a matte finish. This results in very low friction, allowing the cabling to move freely as required by the application and simplify cable tailoring where needed.

Huntsman’s TPU is widely used in automation ▲ ▲ applications

In addition to providing exceptional abrasion resistance and very low friction qualities, TPU also has several additional key characteristics that make it an exceptionally flexible solution for a wide range of environments. This includes good chemical/hydrolysis resistance; flexibility at low temperatures; high elongation/tensile strength; and excellent compression strength. Huntsman can work with customers to offer bespoke solutions, tailored to the specific requirements of an application in order to maximise overall performance and longevity. Huntsman (Germany) GmbH – Germany Fax : +49 541 9141395 Website : www.huntsman.com Conductor preheater Sikora has developed the conductor preheater, Preheater 6000, for cable extrusion lines. During the manufacture of data cables, a reliable conductor preheating is required to ensure optimum adhesion of the insulation on the wire. The Preheater 6000 is

Insulation Shield

Binder tape

Conductor

Jacket

Conductor Shield

positioned before the extruder and preheats the wire using inductive heating, depending on product type, from 100°C (212°F) to 190°C (374°F). Sikora offers the device with the Ecocontrol 600 processor system directly integrated into the preheater housing. The Ecocontrol 600 displays the product and production parameters numerically and graphically on a clear 8.4" TFT monitor, including a trend display of the relevant data, such as temperature and line speed. There is an integrated product library, in which product recipes can easily be stored and recalled. The power required to ensure stable temperature and optimum adhesion is calculated by the Preheater 6000 to suit the line speed and product diameter. Preheater 6000 can be retrofitted into existing lines. Sikora AG – Germany Fax : +49 421 48900 90 Email : sales@sikora.net Website : www.sikora.net

Insulation

HV cable showing conductor, ▲ ▲ insulation and shields

Copperwire Concentricneutral

The addition of other synergistic chemicals can further enhance this resistance down to 5%, low as compared to unmodified LDPE insulation. Lotryl resins are parti- cularly well suited to for this purpose in MV cables. They also improve the resis- tance to stress cracking. Several grades of Lotryl are available depending upon the compounding or mixing equipment used. Arkema – USA Email : info.cable@arkema.com Website : www.arkema.com

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Preheater

6000

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Sikora

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EuroWire – November 2009