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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Advanced rotor technologies' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Raquel Salavessa Energiekontor, Portugal

(1) Energiekontor, Parede, Portugal

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Name: Raquel Salavessa
27.July.1975: Born in Castelo Branco (Portugal)
Graduate in Mechanical Engineering – Lisbon New University (Science and Technology College)
1999 - 2009
Worked on the metal structures business (Inovation & Development, Production, Sales, General Manager assistant).
2007 – 2010
Graduate in Business Management – Lisbon Lusiada University
2010 - …..
Working on the Wind Energy Business as a Project Manager, at Energiekontor.


Rotor blade extension, improving instead of repowering


In the past some wind farms have been installed at sites and had an unexpected low production. Therefore the expected economics was compromised. There are several possible reasons for low production: wind potential prediction too optimistic, wrong type/class wind turbine, decrease of local wind index, low technical availability.

Energiekontor analysed the production on own wind farms and realize that some of them didn’t have the expected production.

The challenge was how to improve the energy production on those wind farms using a cost efficient solution?

Energiekontor and fk-wind, (Hochschule Bremerhaven - Germany), studied possible solutions for this problem.


In 2009, it was designed a solution for increasing the rotor diameter. A prototype was desinged for a blade extension (additional blade tip segment).

Since then, Energiekontor is operating a modified wind turbine (Bonus 54). During the test period, we observed a 7% increase output.

In 2011, was developed a new blade extension prototype, for a turbine Bonus 62. That prototype will be installed and tested. It is expected to have also a 7% increase output.

No exact information about the blades could be made available by the manufacturer, so the tip geometry was taken from an original blade tip and the aerodynamics have been simulated.

Main body of abstract

Some test were made on the modified wind turbine (Bonus 54). For structural loads and deflection of the tip extension a static load test was successfully carried out. A measurement campaign was carried out in two neighbouring turbines. The power production, rotor speed or operation mode, technical availability, wind speed and wind direction were analized. For the natural frequency and fatigue loads we observed similar data and behaviour. Also technical availability was within the same order. The load from the blade root bending moment were nearly identical. No resonance points were detected.
The realized modification confirmed a production improvement of 7%.

In 2013 an inspection, to the modified turbine was made. The transmission shows slight anomalies, but they are considered as normal. All bearings showed few stretch mark formations, which were viewed as resulting from normal operating. The generator and it's aligment did not show anomalies or deviation outside the tolerance range.The powertrain was examined in the area of main bearing, transmission and generator. No critical anomalies were found.The blades were checked and there were only surface damages, which correspond to the original blade and result from normal operation.

For the new extension prototype (Bonus 62), a test phase will be done by FEUP/INEGI (University of Engineering in Porto - Portugal). The assessment of the energy yield modification, load measurements on blade’s roots and main shaft, will be done. Also the natural frequency of the blade, distance from the modified tip blade to the tower and noise measurements, will be performed.


The assembly of the tips will be done on site on a hanging blade. This assembly process is being tested. The overall costs of this modification promise an economic and ecological improvement.

Earlier mistakes on planning and energy prediction can be corrected. More turbines types, in similar wind farms, will be investigated and equipped with an extension in the future. Energiekontor has already the patent for this idea. Furthermore the hysteresis of switching between the two modes of operation will be optimized. This can additionally reduce fatigue loads by minimizing the number of switching events.

Learning objectives
Improving instead of repowering.
New technical, ecological and economic solutions.
New approaches to the existing assets.
Increase efficiency and effectiveness.
Continuous improvement. and development.
Resources optimization.