the cable’s largest expense. Cable and
wire manufacturers have traditionally
used copper as the conductor material
of choice for cables in wind turbines.
However, copper prices are extremely
volatile due to its varying degree of
demand. Therefore, cable R&D engineers
are looking at alternative conductor
materials or copper alloys that perform
comparably to pure copper, but have far
less price volatility.
One such material is aluminum, which
has been used as a conductor material
in wind turbines, but has always been
stiff and not easy to use. Some manufacturers, however, have developed a cable
with flexible-aluminum conductors that
are safer, up to 60% lighter, and easier to
install or replace.
Flexible-aluminum cables are diesel
locomotive (DLO)-like cables, best used
in the tower area of the turbine (second
photo, right), with performance characteristics comparable to standard copper
cable, but at a fraction of the cost.
The cost savings go beyond just switching the conductor material from copper
to aluminum. Installation and maintenance costs are significantly reduced
since the complete power cabling system, from generator to inverter, is only
interrupted in the loop. This maximizes
cable safety and reliability compared to
the conventional installation method,
which interrupts the cable at every tower
section. Furthermore, installation time is
reduced from days to hours.
Additionally, cable connection technology is also seeing a shift to alternative
or hybrid metals, such as lugs being
made completely of aluminum or alumi-num-copper hybrids.
Is the Enhancement
Worth the Cost?
As R&D discovers new advancements
to further product growth, this usually
entails a product price increase to cover
associated expenses, and therein lies the
challenge for suppliers – filtering out what
features are essential from those that
aren’t. In cables for
wind turbines specifically, features that
are added or eliminated depend on where
the cables are used within the turbine.
Cable specifications are created based
on the current state of technology. New
insulating and conductive materials for
cables and wires are constantly being
evaluated for their compatibility. New
generations of highly flexible aluminum
cable up to 34 kV could further change
the kind of installation in the towers.
Insulation material suitable for higher
temperature ranges have a positive
effect on such conversion factors as
deviating ambient temperatures, group-
ing, and at the very least, the laying
method in which cables are installed.
In various wind tower applications the
down tower area, the generator, and the
cable loop are areas with the highest
potential for cost savings. Some manu-
facturers are using special constructions
to separate the cables found in the cable
loop with a spacer. It is mandatory to sep-
arate the cable if the outer insulation is
not abrasion resistant; using cable with an
abrasion resistant outer jacket, like poly-
urethane (PUR), could be a better option
depending on electrical factors like the
current carrying capacity of the system.
Making recommendations about features to include/exclude is challenging
as the use of wind turbines is not a one-size-fits-all situation. There are many
characteristics to consider before selecting the appropriate cable to install in
the turbine. In order to provide the most
cutting-edge, cost-effective solution, it’s
recommended to work closely with your
cable manufacturer’s R&D department.
Regardless of the changes that are
made to components to enhance their
capabilities, if they do not meet certain
standards they can’t be put into production. Some of the most recent developments are the changing of UL standards
with regards to cable and wire requirements in wind turbines. The latest standards are UL 6141 (large wind turbine
equipment), 6142 (small wind turbine
electrical systems), and 6171 (wind turbine tower converters and connections).
These standards specifically describe
the individual components acceptable
for use in wind turbines. They go further
than NFPA 79 edition 2012, which provides only the basic requirements for
cable installation in turbines.
Once these new UL standards are put
into full effect, wind turbine operators
in North America will be required to use
cables that meet the approvals. PDD
Wind cable performance
can be reduced in part
by exposure to extreme
oils and other
stress. It’s important
to work with your cable
manufacturer to select
cables that can withstand these challenges.