Technical Analysis of a Wind Farm in Greece: Identification of Overloads and Wind Sector Management (WSM) Improvement
Introduction
In a wind farm located in Greece, a complex site characterized by extremely high turbulences, recurrent failures were experienced in the turbine blades leading to blade breakage, even on new wind turbines no older than 3/4 years. Our client, aware of the seriousness of the problem, contracted us to perform a Root Cause Analysis (RCA) to identify the source of these failures and the exact time at which they occurred. This analysis focused on determining the limits of the loads and how they exceeded the turbines' capacities, leading to failure.
Analysis of the wind farm
As we conducted the above-mentioned analysis, we found that the wind turbines were exposed to significant overloads due to extreme wind conditions and possible misbehavior under operating conditions. Moreover, we observed that the Wind Sector Management (WSM) provided by the OEM had limited wind directions that did not represent a significant risk to the turbines, and however, the wind coming from the north, which resulted in high overloads, was not limited at all.
The wind in this region of Greece blows with higher intensity from the north, a fact that had been interpreted as a positive factor in terms of profitability, as higher energy production was expected. However, this strategic decision turned out to be counterproductive. Although it initially appeared profitable, the reality was that the turbines were operating under continuous overload conditions, which, in combination with other factors, led to blade failure.
WSM problem identification
The detailed analysis carried out by Nabla revealed that the implemented WSM was not suitable for the extreme wind conditions at this site. According to the IEC 61400-1, when wind conditions exceed those specified in the design, two types of analysis are to be performed: one regarding fatigue loads and another relative to extreme loads and blade deflection. But, in this case, the extreme loads were not taken into account during the initial implementation of the WSM, resulting in a critical design failure.
Improvement proposal
As a result of the WSM analysis, based on a complete Load Assessment, analyzing Fatigue Loads, Extreme Loads and Tip to Tower Closest Approach Analysis, an improvement in the WSM was proposed that included limiting the wind coming from the north and unlocking those directions that were not harmful to the wind turbines. This optimization allowed significantly reducing the overloads suffered by the same thus improving their useful lifespan, and decreasing the probability of having overloads in terms of extreme conditions in the future.
In addition, the implementation of this improvement resulted in a significant increase in the annual energy production (AEP). With the new WSM proposed by Nabla, not only is a better life expectancy and less extreme overloads achieved, but it is also possible to increase the annual production by more than 5% by unlocking wind directions and speeds that are not problematic for the wind turbine and are currently limited, which represents a significant advance in the operational efficiency of the wind farm.
Conclusion
This case in Greece underlines the importance of a thorough and specific analysis when implementing specific WSM strategies at sites with extreme wind conditions. The correct adaptation and improvement of these solutions not only prevents structural damage to the wind turbines, but also optimizes energy production, maximizing the profitability and sustainability of the wind farm.
Furthermore, it is important to understand that the WSM should never be a "fixed photo" using only the preconstructive data. There is a large amount of data that is recorded daily in the wind turbines, that after some time of operation is of great help to review performance and loads, and to refine the WSM. This not only contributes to reducing the risk of failures, but also helps in minimizing the uncertainties and conservatism that are used with preconstruction data, resulting in a more reliable definition of the operational strategy.
If you want to know more about Wind Sector Management Strategies take a look to the next technical article on Advanced Wind Sector Management (WSM) Strategies in Wind Turbines.
