Offshore cabeling: Cabling maintenance planning processes

Cabling, maintenance and planning processes for offshore
wind farms

By Al Tuttle

Despite the battles that were fought about the safety and viability of deep sea wind
farms, builders are getting international permits for more turbines. They are being
built or are approved in some of the angriest waters north of the equator. Compared
to rather mild waters of New England, where the first wind farm on the east coast of
North America has been approved off Massachusetts, the North Sea and Baltic Sea
are more treacherous and unpredictable.

Europe has over 4,000 wind turbines and manufacturing companies of components,
turbines, seagoing vessels and cables are learning more each year about the
process of building a wind farm, according to experts in the undersea cable field.
Power transfer cables are very specialized and made only by a few companies
around the world. Every wind farm uses a complex combination of undersea, buried
cables, turbine connectors, splices and connections at an at-sea substation.

One challenge in the arena of wind technology at sea is developing and refining best
practices for installing arrays of cables in giant fields of wind turbines, said Joel
Whitman of Global Marine Systems. Global Marine is one of the world’s largest
marine cable layers and offshore service providers. (1) The company has worked on
some of the biggest wind farms in the world, particularly in European waters.

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“There are significant problems when laying cable in the ocean that everyone is still
trying to solve,” Whitman said. Installing cable along the seabed means
encountering landscapes as varied as those on land. With miles and miles of seabed
to cross, and with cable to be buried two meters deep, the possibilities for
encountering obstacles that slow or stop progress are multiplied. Companies like
Global Marine use the most sophisticated electronic equipment available to map and
analyze the seabed. There are steep hills, rugged bottoms and material that ranges
from mud and silt to hard clay and rock.

There are always a great number of unknowns when a
project the size of a wind farm at sea is being
developed. While the water is generally 70 meters
deep or shallower, the cable is exposed to powerful
stress forces when installed and being buried, or while
connected to the Whitman said. Some of the
arguments used against giant wind farms are ironically
environmentally based. As a power source born and
developed in part because it uses no or very little
fossil-based fuels, the natural view of wind power is
that it is supremely clean and friendly to every
environment. Since each tower is the size of the
Statue of Liberty and a field can be 100 square miles,
some groups against seaborne wind power say that the
Photo courtesy Siemens
energy needed to create all the parts, put them in the
ocean and connect them, is more than the energy the wind farm can create in
several years’ production. These groups decry the pollution supposedly created by
this manufacture and construction. They also claim that in spite of the 4,000 units
working in Europe, none of the electric rates paid in affected countries have gone
down. Some people also argue that fishing areas and shipping lanes are threatened
by giant wind farms.

Extensive right-of-way negotiations can solve many of these navigation problems.
Those negotiations must be part of a deeper research and development plan for

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each project. Wind farms are still trying to reach a point of profitability, Whitman
said, because the companies and consortiums put together to build and operate
them have not planned every step completely enough. More companies working
together will benefit every wind project, he said. These larger groups of manpower
and machine power, combined with more experts researching every part of the
plan, will make every project more complete before any work is done in the water.
“When everything is running well, the whole system is profitable,” he said.
Seaborne wind farms have no construction impact on property (as do land-based
farms), no noise pollution problems and are generally not a threat to visibility.

However, many of the projects Global Marine has been involved with run into
problems that take a lot of money to fix. The turbines are linked in a line, so that if
one goes out of service due to a cable problem,
the rest in front of the down turbine all stop
working. “If the last turbine is out, it is the only
one out and is not as much of an emergency as
is a turbine that goes down and stops all the
rest with it,” he said. The result is an
emergency need for cable, crews and ships.

Photo courtesy Siemens The supply of cable on hand is critical for
repairs. Whitman’s company has been involved
in projects that did not have enough backup cable on hand. In one instance,
Whitman said that the wind farm operators had asked for only one mile of cable be
stored as inventory for an emergency. That is less than one length of connection
cable between two turbines. When a turbine cable far up the line failed, the
company waited weeks for more repair cable to be made, Whitman said. So an
extremely expensive supply chain problem occurs in the repair and maintenance
area when not enough cable (and other contingent supplies) are not kept on hand.
Regular maintenance has not been addressed in depth either, according to
Whitman. Checking connections and cable is not a perfect art, but is necessary and
is an area that needs more specialized equipment. Every tower is made in four
parts: the original electrical connection is made before the turbine is placed on the

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transition piece. After the turbine is put onto the assembly, that connection
becomes more difficult to inspect and replace or repair. The same is true for cable
running between turbines, connecting them in a line, and for cable running to and
away from the substation. When cable is inspected and tested at the factory, it is
easier to detect defects visually. After cable is buried and tests are completed for
every section, the cable becomes exposed to the underwater environment on a
permanent basis. This is a challenge to the rugged reliability of the cable,
connections and turbine construction.

There are only a handful of companies supplying undersea power cable. The
seagoing environment is far different from land-based wind farm tracts. There are
pluses and minuses for either environment: the sea has no surface terrain but the
seabed has a variety of landscapes. The cables are made under strict quality and
environmental rules by companies like nkt cables of Denmark (2), which is a world
leader not only in cable manufacturing but in research, safety and technology. The
company is researching more durable materials for use in cabling. They are also
very concerned about using as environmentally friendly materials as possible. nkt
cable replaced dangerous materials like lead and PVC in its cable products.

It is becoming more obvious that not only are wind farms here to stay, but more,
bigger projects are on the way. In Denmark, Germany and England, projects are
planned using even bigger wind fields and bigger turbines. In the case of farms
planned for the Baltic and North Seas, extremely complex connections and farm
hubs are planned, with power going to several countries. (3) These projects add
layers of complexity to the entire construction process: supply and security, land
and water lease, manufacturing prediction, quality support and more. According to
experts like Joel Whitman, this complexity demands that the partners in the project
broaden the scope of planning and consider more redundancies than have been
included thus far. One of the critical areas that needs a longer look is maintenance.

Now, many years after the building of the first offshore wind farms, evidence is
building about the need for more comprehensive maintenance programs and backup

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equipment. According to one report (4), these huge yet extremely precise machines
are beginning to need repair or replacement. The report notes that turbines in the
North Sea are expected to last 20 years but some are failing at age eight. It could
simply be the very difficult North Sea conditions, but those conditions are prevalent
in other European waters. Finally, the report notes that the expenses of building
each completed turbine has exceeded estimates while output has been less than
expected, in megawatts/unit.

As the size of farms increases and more farms are planned, the final maintenance
and contingency inventory and funding must be increased. That comes from better
overall long range planning. The more experience operating consortiums have at
maintaining an average wind farm, the better they will be able to anticipate
maintenance problems.

Al Tuttle

Freelance Editor

Al Tuttle is news and features editor whose experience includes Media News
Group, Reed Elsevier and New York Times New England. He specializes in industrial
and commercial writing. He was in sales for industrial distribution companies and
manufacturers for 15 years.

1. http://www.globalmarinesystems.com/Capabilities/subsea_cable_maintenanc
e
2. http://nktcables.com/Products/Offshore

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3. http://www.ewea.org/fileadmin/ewea_documents/documents/publications/re
ports/OffshoreGrid__report.pdf
4. http://www.forbes.com/sites/energysource/2012/01/11/shaky-foundations-
for-offshore-wind-farms/

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Offshore cabeling: Cabling maintenance planning processes

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