YCE: a provider of applied structural engineering solutions

Wind blades are subject to adverse weather conditions such as lightning strikes and wind erosion.

All repairs are carried out at height; YCE Repair System guarantees that maintenance and repair activities meet the following general technical criteria:

Duration: The repair must be able to offer a service life at least equal to the original state of the blade, maintaining its integrity under the same fatigue loads and environmental conditions. Repairs by adhesive bonding must not significantly degrade over time.

Stiffness: The repair should allow the original composite structure to maintain its optimum stiffness strength. The repair must permit only minimal changes to the load paths.

Surface finishing: The surface finishing of the repair must keep the aesthetic appearance, UV resistance, resistance to chemicals and the aerodynamic properties of the original construction.

The repair activities are carried out according to the following technical standards:

– Deutsches Institut für Bautechnik – DIBt -, Berlin Richtlinie für Windenergieanlagen, März 2004
– Det Norske Veritas – Design and manufacture of wind turbine blades, offshore and onshore wind turbines, October 2010
– Germanischer Lloyd – Guideline for the Certification of Wind Turbines, Edition 2010

YCE Repair System: priorities of blade repair design

Complete repair of the blade at height, from both the structural and aerodynamic point of view

Respect weights
Work efficiently

We design and build all our spare parts in-house:
– In the absence of as-built data we perform reverse engineering of the blade structure
– We build the moulds needed
– We produce in our factory the spare parts needed for our repair work

We do specific R&D activity
– Advanced structural repair techniques
– LPS retrofits for several different blades
– Anti-ice coating application

Extraordinary shell damage and YCE repair techniques

Lightning strikes generate a heat-shock that reaches temperatures above 3,000°C for some tenths of a second. The presence of unrepaired cracks and minor damage on the surface of the blade causes the seepage of water inside the blade. When this water is subject to very high temperatures, the instant evaporation causes the resulting gases to expand very rapidly: a violent explosion takes place.

Since this happens during bad weather conditions, the wind tower generator is at the same time subject to high winds: the explosion causes the two shells that form the blade exteriors to split open and be torn away.

YCE repair techniques provide the perfect reconstruction at height on average within 5 days.

YCE has developed specific repair procedures for traditionally built blades and for the more innovative “one-shot” Siemens blades.

However, such damage can be prevented: constantly monitoring and evaluating the state of the blades allows for early identification of critical conditions and the subsequent timely programming of maintenance, thus reducing the probability of extraordinary damage.

The repair procedure for such damage involves in the reconstruction at height of the blade, using spare shells:

– damaged parts are removed, application area is cleaned and rectified;
– damaged blade is reconstructed using spare shells;
– detailed final reconstruction of the airfoil is made by bodywork and the final sacrificial layer (the layer that protects blades from several damage causes) is reconstituted with gelcoat.

Structural damage to spar and composite sandwich laminates

Following YCE procedures, as per best practices suggested by internationally approved technical rules, partially damaged structural parts are reconstructed by substituting the missing fibres, respecting orientation and volume.

Particular attention is paid to the original specification of the blade in the area of the repairs, especially when the damage is over a wide area.

Work is carried out in line with YCE procedures within specific weather ranges, according to material specifications and techniques used.
Monitored data includes temperature and humidity.
Formal work instructions issued by our structural engineers to repair teams prescribe the use of specific materials.

Erosion and cosmetic damage

Erosion and the ageing of the sacrificial layer are the root cause of structural damage leading to long downtimes.

YCE has developed specific techniques to address the deterioration of the sacrificial layer, which is the layer that protects blades from several damage causes (UV rays, erosion, etc.).

Timely maintenance of the sacrificial layer ensures wind blades have a longer worklife.

LPS Retrofit

Most wind blades, even the newest designs, are damaged by lightning strikes. Apart from the immediate damage caused by the lightning (the formation of plasma that burns the sacrificial layer of the blade), overheating caused by the intensity of the current through the earthing system causes the vaporization of the water that found its way inside the blade.

The instantaneous transformation of this water into gas and its immediate expansion cause mechanical damage to the tip area.

YCE research has developed a retrofit that improves LPS (Lightning Protection System): YCE LPS RETROFIT®.

YCE LPS RETROFIT® prolongs the lifecycle of the blades by extending the electrical attraction area of the receptor, mechanically strengthening the blade tip and improving the Lightning Protection System.

Anti-Icing Coating

Why Anti-Icing?

Ice on the blades is due to the adhesion onto the blades of supercooled droplets of water contained in the clouds.
The accretion of these initial supercool ice crystals forms a cold substrate to which increasingly larger ice crystals at normally cool temperature adhere.
After some time, ice accretion is so widespread that the rotor is stopped because of the vibrations caused by the uneven weight accumulation.

Potential damage to the wind generator

Initially the output of the generation will be lower due to the uneven weight added by ice, and then the unbalanced rotor causes wear of the transmission and the gearbox.
The ice itself causes cracking of the sacrificial layer through infiltration in the gelcoat.

The YCE solution

The YCE Repair System solution is to apply a superhydrofobic coating that reduces and prevents supercooled droplets from adhering to the blade surface. Anti-Icing coating is a special coating capable of withstanding the wear-and-tear of atmospheric agents and preventing the accumulation of ice and all subsequent potential damage.

Anti-Icing Coating also improves the protection of the leading edge of the blades, thus increasing the efficiency of the wind generator.