sparks
ELECTRICAL NEWS
june 2014
12
contractors’ corner
THE penetration of water or the existence of
moisture in XLPE cables is one of the most
unacceptable problems associated with the
lifespan of the product especially under the
influence of high electrical stresses. XLPE
insulated cables that are designed to operate at
600/1 000V require insulation thicknesses well
above those required purely for electrical per-
formance. The electrical stresses experienced
by LV XLPE cables are too small and insufficient
to create electrical failures due tomoisture
hence, no protection from the effects of water
andmoisture is required for LV XLPE cables.
Medium voltage XLPE cables (>1 000V),
experience significantly increased electrical
stresses and should be protected against water
penetration andmoisture. MV XLPE cables can
be protected by radial or longitudinal protec-
tion against water penetration. Water is able
to penetrate the cable through outer sheath
damages at the joints or termination ends. Lon-
Picture 1. Water swellable materials can
be hard water blocking compounds or dry
materials such as water swellable powders
or water swellable tapes and yarns.
Water blocking in medium voltage XLPE cables explained
gitudinal water blocking is the most appropriate
means of protection for MV XLPE cables.
Water blocking techniques
Water blocking is realised through the prevention
of water flow inside the cable as well as between
the elements of the cable.
This is achieved by filling the free space within
the cable with water blockingmaterials. In the
instance of water penetration through a dam-
aged outer sheath, the water blockingmaterials
will start the blocking process against water and
moisture ingress.
Each stage of the cable design is analysed and
all interfaces within the cable are water blocked.
Where electrical contact is required between the
interfaces of the cable, then semi-conductive
materials are utilised.
Water blockingmaterials
Water swellable materials (
Picture 1
) can be hard
water blocking compounds or dry materials such
as water swellable powders or water swellable
tapes and yarns. The use of tapes and yarns was
found to be the most appropriate method of
water blocking from a manufacturing and an
application perspective.
Water blocking of conductors
Water blocking of conductors is a crucial step in
the design of the cable. This is achieved by ap-
plying a yarn in the centre of the conductor and
water swellable tapes over each layer of wires.
Picture 2(a)
shows an example of a conductor
with water swellable materials;
Picture 2(b)
as it
turns blue in the presence of moisture.
It is essential to ensure that conductivity
of electrical current is maintained after apply-
ing tapes to the conductor. This was tested by
measuring the resistance of the conductor.
Aberdare achieves this through compaction of
the conductors. Compaction of
the conductors with the tapes
forms a framework structure on
the tape thereby maintaining
conductivity.
Tests were conducted at
Aberdare’s laboratories in
Port Elizabeth to verify the
increase on conductor tempera-
ture due to the additional tapes
within the conductor. The tests
were witnessed by customers
from Eskom Brackenfell and
City Power.
The specification states that there should be
nomore than a 2°C temperature change when a
cable connector is applied. This test is called a heat
cycling test. The test was successfully passed and
the results verified. Samples have been sent to a
testing house in France to conduct further load
cycling tests. Verification of all tests has a huge
benefit for installers as they would not be required
to remove the tapes when jointing or terminating
cable ends.
Water blocking of amouring
Water blocking of armouring is achieved by ap-
plying a generous layer of bitumen to the armour.
This seals the crevices between the armour wires
and enhances the corrosion resistance of the
armouring
(Picture 3).
Enquiries: (011) 396-8000
Picture 3. This seals the crevices between the armour wires and enhances
the corrosion resistance of the armouring.
Picture 2(a) shows an example of a conductor with water
swellable materials.
CWIEME Berlin, theworld’s largest andmost com-
prehensive event in the coil winding, insulation and
electrical manufacturing industry will be held from
24 to 26 June at Messe Berlin, in Germany.
Over 7 000 engineers, designers, buyers and
academics fromaround theworldwill visit CWIEME
Berlin 2014 – the largest annual meeting place for
the global coil winding, insulation and electrical
manufacturing community.The three-day event,
held in Germany’s buzzing capital, will feature some
750 suppliers fromover 40 countries – including
top names ABB, Alstom, EuroTanciatura, Hidria,
Voestalpine andVon Roll – displaying the latest coils,
electricmotors, electromagnetic insulationmaterials,
transformers and repairs solutions.
Coil winding expo in Berlin
Now in its 18th year, CWIEME Berlin 2014 is set to
be bigger and better than ever before with a wide
range of products on show.
“CWIEME Berlin is not just an opportunity to source
newproducts and suppliers, but to network, keep an
eye on the competition – and learn about all the latest
trends and technical advances,”says ChloeTheobald,
content manager for CWIEME Berlin.
At CWIEME Central, themain seminar hub, visitors
will be able to attend technical presentations and
panel discussions on topics such as:
• Revenues, regulation and market opportunities for
the LV andMVmotor industries.
• Wireless power transfer and inductive charging de-
sign for increased e-mobility.
• Advances in OIP bushings for improved safety
in HVDC equipment.
• REACH and the ‘Greening’ of technology de-
bate.
• Climatic resilience and risk mitigation for off-
shorewind transformers.
• Breakthroughs in nanoscience discoveries of
newmagneticmaterials.
Speakers will include top industry experts: Prof
Ivan Schuller, director of the Centre for Advanced
Nanoscience (CAN) at the University of California-
SanDiego; Paulo Cardano, (OIP Bushings, Alstom
Grid); Prof MartinDoppelbauer (Karlsruhe
Institute ofTechnology); Dr RolfWinter, (Electrical
Winding & Insulation Systems Division) at ZVEI;
andDr FaicalTurki (Paul Vahle GmBH).
Meanwhile, CWIEME Berlin’s MachineryTrail will
provide regular live product presentations and
machinery demonstrations across awide variety
of exhibitor stands, allowing visitors to see the
latest technology in action.
Enquiries:
A link to your
Wireman’s License
Go to:
and click on the P &TTechnology logo.
Picture 2(b) shows that it turns blue in the
presence of moisture.
