Technical article
November 2014
48
Developments in green
technologies for power
cables – using clean
materials in the
production process
By Sikora AG
Introduction
Green technology is a topic which plays
an increasingly important role worldwide,
especially in light of greater shortages of
resources and increasing environmental
pollution.
Industry has an obligation to develop
products
and
processes
that
are
sustainable, energy saving and environ-
mentally compatible. At the same time,
these products and processes have to be
highly profitable.
Crude oil is a basic irreplaceable
resource. Oil is used in the form of plastic
materials for cable insulation. Sikora’s
understanding is to provide technical
solutions for online quality assurance of
materials and cables to enable economic
and ecological production processes.
By integrating measuring and control
as well as inspection and sorting
technologies in the production line,
the scrap rate can be reduced and
consequently material saved.
Every litre of oil that can be saved due to
lower rejection rates and less material
consumption also conserves the less
available resource.
This article introduces a novel tech-
nological solution that inspects the
purity of XLPE pellets that are used at the
insulation process of power cables.
It is the first system on the market that
inspects pellets to 100 per cent and
automatically sorts out contaminated
pellets before they get into the extrusion
process. By assuring absolute clean
insulation material, the system supports
the requirements of green technology
within the process chain. The technology
is the result of a development cooperation
between Sikora and Maillefer.
Necessity of clean
XLPE compound
for power cables
The purity of the XLPE compound that
is used for the insulation of power
cables plays a critical role. Perfectly
pure compound reduces the risk of a
breakdown.
Metallic impurities of 50
μ
m may cause
damage to the end product with high
follow up costs that can easily run into the
millions.
The repair of a defective submarine cable,
for example, which has been damaged
by contamination, can lead to weeks of
downtime.
It is for that reason that the Chinese
Standard for high voltage cables,
for example, demands the exclusion
of contamination from 75
μ
m in the
processed materials.
Accordingly, it is necessary to inspect the
material to 100 per cent before it enters
the end product. Sample tests are a first
step but not sufficient to exclude all
contamination reliably.
Today, cable manufacturers use screens to
catch impurities in the XLPE compound
before they get into the cable.
The screens are positioned directly in the
melt flow after the extruder, before the
crosshead.
However, these screens can get clogged
by scorches or excessive amounts of
contaminants after a certain run time.
Then the melt pressure in the extruder
may increase significantly. Finally, the
production has to be stopped in order
to change the screens, which in turn
means that later a joint is required at that
position.
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▲
Metallic contamination inside the pellet (X-ray)
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“Black specs” on the pellet (big and small) (Optical)
