With Larger Rotor Blades, New Strains Come into Play External wear and tear such as erosions on the leading edge of the rotor blade, tension cracks as well as large-scale UV damage are common fatigue phenomena. But with rotor blades being extended by up to 15 metres, new strains come into play, as Tilman Weber explains in his article "Robust Blades and Foundations" published in Erneuerbare Energien in February 2014. Read the full article for free here: http://bit.ly/WeberArticle

1. Special maintenance services keep propellers, foundations and even towers in working order.
Their service is more important than ever.
Robust Blades and Foundations
TITELTHEMA
40 ERNEUERBARE ENERGIEN | Februar 2014

2. Three years ago, the German Wind Energy
Association (BWE) discovered the theme of
specialist maintenance for themselves. "Our
working circle already existed years ago," says
Stefan Brassel, spokesperson for the Association's
own circle of experts AK Rotorblatt. It has been
firmly established at BWE since 2010. Here experts
on rotor blade repair develop criteria for "what
measure of tolerance the thickness of an adhesive
layer or a bridge position on the belt should have."
These internal structural components give the rotor
blade the necessary stability, but can also be
potential breakage points. The BWE working circle
spokesperson is also in charge of rotor blade
maintenance at Deutsche Windtechnik in Bremen
and is already familiar with the problem: Until now
rotor blade manufacturers saw little need for sharing
data. The BWE working circle has put together a
damage catalogue with threshold values since then.
It indicates what treatment would be most suitable
for the respective severity of damage.
Weak blades reduce the income
The necessity for this self-help in spite of wind
power development having been producing power
in the gigawatts for many years is due to an
erroneous development. Independent service
providers and turbine manufacturer maintenance
services have long competed over the maintenance
of connecting rods, electronics or control systems.
But the manufacturers often left the rotor blades or
foundations to specialist firms. This is because the
knowledge and climbing skills along turbine blades
have little to do with the traditional machine-
building know-how of standard maintenance
services. Rotor blades and foundations therefore
require specific teams, whose members often had to
undergo expensive training. Yet, the main reason for
part maintenance is not so much to avoid major
accidents. "Often the base coating suffers damage
through erosion," emphasises Brassel from the BWE
working circle.
New rotor blades often used to lack plastic films or
double coatings, which are nowadays a requirement
for large rotors. Because even small rotor
weaknesses can cause large losses of revenue using
cutting-edge wind farm technology, plant
manufacturers have started to recognise the value
of good foundations, towers and particularly rotor
blade maintenance. "Turbine manufacturers had
already started putting together maintenance teams
for rotor blades three years ago," says a wind farm
developer, who does not want to be named.
According to interviews with randomly selected
German project developers, ERNEUERBARE
ENERGIEN attributes a long tradition to Enercon in
this area. But Vestas and Nordex also count as
pioneers. In 2008, the Spanish service provider GES
took over the rotor blade repair company WKA
Service Fehmarn. Nowadays, it maintains around
700 power plants every year using 130 technicians.
The contractors are turbine manufacturers that hire
GES as a subcontractor as part of their manufacturer
service. Elsewhere in Europe, the GES maintenance
section with 40 additional maintenance technicians
is also booked by energy companies, stresses the
CEO of the GES subsidiary in Germany, Arkin
Pariltan. He adds that improved resins for gluing
loose blade structures or optimisations in the
protective layers against UV radiation from the sun
increase quality of his company's service. Other
specialist maintenance companies particularly
define themselves with their staff's abseiling
techniques to provide a service on those long,
Good maintenance, good efficiency Rotor
blades at wind energy farms have until now
largely been maintained by specialist
maintenance companies. Yet turbine
manufacturers are beginning to employ
crews to remove surface erosion or damage
to the leading edge on rotor blades for
more effective operation.
Foto:Seilpartner
ERNEUERBARE ENERGIEN | Februar 2014 41