Cable damage can be expensive

can be
Cable damage accounts for a large proportion of damage claims
settlement in offshore wind farms. New concepts such as cable-­
in-pipe or the 66 kV cable are designed to reduce costs.
have such a breakdown,” says Beck.
laying. It can take half a year for a
all offshore wind pro-
Of course, the high costs associated
ship to be on site to repair a defec-
jects have had at least
with export cables are responsible
tive cable. Cutting out and bypass-
one instance of cable d
­ amage,” ex-
for the dismal figures. On average,
ing the defective section of cable is
plained Martin Beck from Marsh
inter-array network (IAN) claims
then only a matter of about 10 days.
GmbH in a lecture at the 4th Off-
cost insurers between 1.2 and 2.6
shore Days in March 2017. In terms
million euros per wind farm if you
of both the types of damage and
expect one damaged cable during
Burying to avoid
external loads
the amount of compensation paid,
In the context of this huge expense,
cable damage tops the list: 40 % of
damage occurs once every 600 km
efforts to reduce costs through new
the damage covered by insurance
per year.”
concepts are understandable, but
is related to cable defects, but the
The high costs for cable
damage prevention is also
share of the total compensation
repairs arise not least be-
paid is 83 %. The key takeaway is
cause only a few spe-
this: cable damage can be expensive.
cial ships are avail-
But how does damage to inter-array
able – and these are
main causes of
cables compare to that of export
damage to inter-
cables? “Unfortunately, we do not
elsewhere for cable
array cable can be
a focal point for c­ able
Photos (2): Van Oord
inety five percent of
logistics &
Installation of infield cable
covered, but buried several metres
with a capacity of 28 MW will use
deep in a trench and then backfilled.
and test a series of future offshore
The real fault lies in how the cable is
wind energy technologies for the
buried and not in the lack of cover-
first time. Innovations include a new
ing of the cable.
foundation concept (gravity jackets),
After the burial, there is little
inter-array cabling with a doubled
scope for influencing the position of
voltage level of 66 kV and the cable-
the cable. Actually, all that remains
in-pipe concept,” says Siemens press
is to measure the depth of the cov-
officer Bernd Eilitz.
erage. The company Patzold, Köbke
For the first time in an offshore
­Engineers GmbH & Co KG in north-
project, the cable-in-pipe concept
ern Germany specialises in cable
uses much cheaper onshore cables.
depth exploration using several seis-
Conventional cables have an outer
mic and magnetometric methods.
layer of insulation, which must
at Eneco Luchterduinen
of course be extremely saltwater-­
­tested in practice
Wherever there is high cost pres-
explains the trick behind the cable-
found in transport, faulty design and
sure, innovations are not far away.
in-pipe concept: “In the Nissum
manufacture, improper installation
Nissum Bredning Vindmøllelaug
­Bredning project, we simply laid the
or, later, by the legs of the jack-ups
and Jysk Energi have won the
cables in plastic pipes that are protec-
or the anchors of other vessels that
Danish Energy Agency’s (DEA)
tive but also inexpensive.” This saves
enter the wind farm without per-
tender for the construction of the
considerable costs – but the savings
mission. Often one type of damage
28 MW ­Nissum Bredning Vind pilot
depend on the size of the project,
leads to another. Thus, the anchor of
project. Nissum Bredning is an inno-
and no one wants to reveal details.
a ship can actually only damage the
vation project in northern D
­ enmark.
It is currently a proof-of-concept
inter-array cable if the final burial
When the four 7 MW turbines are
test. Eilitz emphasizes that, “To our
was not deep enough. The cable is
connected to the grid in the pilot
knowledge, Nissum Bredning is the
usually buried with a sea plough
project, a new cable concept will
first project where onshore ­cables are
by an underwater vehicle, not only
be put to the test. “The pilot project
being used in plastic pipes.”
Foto: Kristina Becker
­offshore wind park
for use in marine wind farms. Eilitz
Foundations by EEW SPC
EEW Special Pipe Constructions GmbH,
On average, inter-array network
(IAN) claims cost insurers between
€ 1.2 and 2.6 million per wind
farm if you expect one damaged
cable during construction. During
­operation, damage occurs once
every 600 km per year.
offshore wind farms for the past
year and a half. The type test of the
66 kV Inter-Array line was successfully carried out in accordance with
CIGRE and IEC standards.
A year ago, the cable-laying
company VBMS ordered Nexans
­cable technology for the world’s first
66 kV rather than
33 kV
66 kV offshore wind farm. The Blyth
electricity is then stepped up to ex-
Offshore Demonstrator Wind Farm
tra-high voltage – generally 380 kV.
is located 5.7 km off the coast of the
A voltage of 66 kV in the Inter-array
If the voltage level in the wind
small English town of Blyth (North-
network is not quite as new – a 33 kV
farm is now raised to 66 kV, energy
umberland) and consists of three
line has been the standard to date,
infrastructure costs can be saved by
strings with five wind turbines each.
but could soon be replaced by the
reducing the number of transformer
A network of separate 66 kV
66 kV power cable as the standard
platforms. In addition, the cost of
interconnecting cables and export
solution. With their higher voltage,
maintaining and repairing the net-
cables transports the electricity to
66 kV cables can transmit greater
work will also be lower. Reduced
shore. The 66 kV submarine cable is
power with a smaller cross-section
voltage losses at higher voltage
manufactured and tested at Nexans’
and lower current than conventional
levels, can account for around 15 %
special factory in Hanover and de-
33 kV cables. Higher voltage means
of the total costs of a wind farm over
livered in one piece. Nexans Power
lower cabling costs and fewer losses.
its entire operating life.
Accessories manufactures the suit-
The existing voltage level of
Following an extensive certifi-
able connectors, which were devel-
33 kV means that the energy gener-
cation process, cable manufacturer
oped on the basis of the established
ated is converted into high voltage
Prysmian has been offering 66 kV
33 kV technology, in Erembodegem,
at a substation at sea. On land, the
cables for inter-array networks in
Our Ports.
Your Future.
Jörn Iken
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