EoW November 2009

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EuroWire – November 2009 54
Power cables
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%.
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:
Website:
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.
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.
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:
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
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: Website:
Huntsman’s TPU is widely used in automation ▲ ▲
applications
Preheater 6000 from ▲ ▲
Sikora
HV cable showing conductor, ▲ ▲
insulation and shields
Insulation
Shield
Insulation
Copperwire
Concentricneutral
Jacket
Binder tape
Conductor
Shield
Conductor