BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

182 Mihai Florin Mănescu and Valeriu Panaitescu
2.2. Discussion
The advantage of the thermographic method is that this technology is able
to produce an overall picture of the whole wind farm. A quick assessment can
be made by a user with some experience. The main problem with this method is
that the thermal images are limited to some electrical components that produce
excessive heat during operation. This can also be applied to defective
components if they move excessively, causing friction and heat.
The ultrasonic methods will not detect single fibre breaks or composite
materials. These methods do not work for complex structures (only the blades,
the tower and the nacelle can be monitored).
An advantage of the X-ray technology is that the images are obtained in
parallel, not through scan as is the case with the thermographic approach and,
therefore it is faster. However, problems can appear when the X-ray image is
interpreted. It should be noted that the sources emitting the X-rays are small and
air-cooled, thus fulfilling the safety prerequisites and they can also be controlled
remotely.
3. The Damage of the Structural Integrity of the Wind Power
Impairment can occur in any component or part of the turbine and it can
take any form, ranging from a crack in the concrete foundation to a split blade.
Various cases of structural damage are reported from time to time in several
countries such as Wales, Scotland, Spain, Germany, France, Denmark, Japan
and New Zealand [8]. In Germany, in 2002, a blade broke away, and parts were
found scattered throughout the area [9]. In another case, a blade flew to a
distance of 8 km and entered the window of a house. A detailed documentary of
this accident is available http://www.caithnesswindfarms.co.uk. According to a
survey performed in Germany [10] the frequency of damage is almost equal for
all the mechanical systems and structures. The failure varies from 4% for the
structural parts and the gear to 7% for the rotor blades.
Although structural damage may occur in any component, the most
common type of damage is encountered in rotor blades and in the tower [11].
Special attention is given to the blades, as they are the key elements of a wind
power generation system and as their cost can average 15-20% of the total cost
of the turbine. It was noted that the damage to the blades is the most expensive
type of repair and also the one which lasts the longest [12].
Additionally, even minor damage on the blades can lead to serious
secondary damage to the entire wind turbine system when action to repair it is
not taken immediately, leading to the collapse of the entire set [8].