UNEXPLODED ORDNANCE - Wind Energy Network

Sponsors of GEARBOX V DD
Gearbox v direct drive
......or is there another way
The debate as to whether or not
the conventional wind turbine drive
train with a gearbox at its centre or
whether the direct drive concept is
better has been aired for many years
now and the arguments from both
sides are well known.
Personal biased consideration
Naturally depending on where you stand
your argument will tend to favour what
is best for your business and objectivity
may be skewed towards personal
considerations. It is clear however that both
sides of the argument have positives and
negatives, nothing is perfect. In an ideal
world we would be able to keep all the
positives and lose all the negatives, but this
is never going to be completely possible. It
should never however stop us from trying. If
we never try we will never succeed.
Focus – reducing the cost of
wind energy production
Some years ago two companies in Finland
put their thinking caps on and tried to
picture where the future of wind turbine
technology would take us and their stated
goal was to reduce the cost of wind
energy production.
It was clear that ever larger wind turbines
would be the order of the day as our
industry has accelerated from kW class
to multi MW class turbines in a very short
period. Our industry is still an infant but
turbine generation capacity has leapt from
100kW to 7MW and beyond in only 30
years.
Size and weight
The resultant increase in component
sizes to meet this massive increase in
generation capacity is also massive and
it is becoming a potential limiting factor
to the economics of turbine growth.
The two companies from Finland; one a
gearbox manufacturer (Moventas) and
the other a Permanent Magnet Generator
manufacturer (The Switch) clearly identified
size and weight as becoming limiting
factors in both conventional and direct
drive turbines and decided that a solution
needed to be found.
Other considerations
Size and weight were not the only
considerations taken into account by
Moventas and The Switch. Other factors
were carefully considered with the goal of
reducing the cost of generation.
One such
consideration was
the ability to perform
service to the unit on
site in the nacelle. This
consideration was
particularly relevant
with the increase
in the number of
turbines being
situated offshore.
The costs associated
with lifting a gearbox
or, as is in some
cases a complete
nacelle, from an
off-shore turbine is
extremely high and
can only be achieved
using specialist lifting
vessels that are not always available and
may have limited operating windows due
to weather constraints in certain areas.
Ease of service
Considering ease of service is of course
important as it is a universal truth that
all machines have the potential to fail,
therefore it is important to make provision
for this when you design. It is also a good
idea to design something which will be
as reliable as possible and this became
an important driver for Moventas and The
Switch and can be summed up in the
statement below.
“Increasing reliability by reducing system
complexity is key in reducing cost of wind
energy production”
Reduction of complexity
So in order to increase reliability the
complexity of the system must be
reduced. On a drivetrain level the result is
the integration of the independent main
components into a hybrid system. On the
gear level, the result is fewer components
used. The design concept is based on
load sharing techniques and the result is
minimisation of total mass, with optimised
and verified load sharing between the
components transmitting the load and
the resultant medium speed technology
ensures the highest availability and annual
energy yield.
Comparisons in reduction
The gearbox and generator combination
that has been developed in partnership
between Moventas and The Switch is half
the size and weight of direct drives. When
compared to conventional drive trains the
overall length is significantly reduced and
also weight reduction is achieved. Lower
weights and smaller physical size provides
the opportunity for reduction in the total
turbine manufacturing costs as towers and
foundations are not supporting such heavy
weights and sizes.
Total nacelle size and weight is
dramatically reduced. Further savings
are made in reduction of transport costs
associated with larger heavier structures in
the multi-MW turbine classes.
The stated goal is – “reduce the cost
of wind energy production”
To achieve this
• An increase in reliability based on
simplification of the system complexity
is needed
• Size and weights need to be
significantly reduced
• Total life time costs need to be
reduced by making total service
possible on site
• Use best technology to increase
annual yield
The result is – Fusion Drive from
Moventas and The Switch.
Moventas
www.moventas.com
Click to view more info
The Switch
www.theswitch.com
= Click to view video
www.windenergynetwork.co.uk
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