Advanced Engineering for G47 Mainframe Cracks

The occurrence of cracks in the mainframes of G47 and V47 wind turbines is a widely recognized issue in the wind energy sector, especially in localized areas of the mainframe associated with welded joints. These cracks are typically caused by stress concentration factors arising from both the structural design of the mainframe and its manufacturing process. When this structural configuration is subjected to the cyclic loads inherent to wind turbine operation, the risk of fatigue cracking at critical points increases significantly. In response to this, Nabla Wind Hub applies advanced engineering solutions to identify, analyze, and mitigate these structural damages, extending asset life and ensuring safe and efficient operation.

Gamesa G47 Mainframe most critical Checkpoints

This case study focuses on a specific wind farm experiencing structural damage in a significant portion of its fleet of Gamesa G47 wind turbines. Due to cracks and deterioration in the mainframes, several machines were out of service, resulting in high operational costs for the client. The main goal of the project was to design and validate a damage mitigation plan to keep as many turbines operational as possible, while minimizing downtime and associated costs.

To develop an effective damage mitigation plan, a detailed analysis of the structural condition of each turbine was conducted, specifically focusing on the type and progression of the cracks detected in the mainframes. The technical approach was based on evaluating the feasibility of crack-arrest holes, a technique widely used in structural engineering to slow crack propagation by redistributing stress at the crack tips, thus reducing peak stress concentrations.

Global model with crack-arrest holes

In the first phase, following a field inspection and measurement campaign, the affected wind turbines were classified into different groups based on the length of the existing cracks. These ranged from 150 mm — the threshold established by the supplier — to over 300 mm in the most critical cases.

Next, the site’s wind conditions were analyzed, and aeroelastic simulations were carried out to develop a representative model of the G47 wind turbine’s dynamic behavior. This aeroelastic model served as the foundation for a Finite Element Analysis (FEA), in which both the cracks and the crack-arrest holes were incorporated to validate their effectiveness.

During this analysis, different combinations of crack lengths and hole diameters were evaluated, ensuring that the structural components maintained integrity under both extreme loading and fatigue conditions. The results showed a significant reduction in stress concentrations at the crack tips when the arrest holes were introduced, confirming the suitability of this solution to extend the service life of the affected wind turbines and ensure their safe operation.

The implemented mitigation plan, tailored to the specific conditions of the wind farm, allowed wind turbines to be classified by criticality level and addressed with differentiated solutions: some wind turbines were returned to normal operation, while others were operated with certain limitations, depending on the degree of identified damage and risk level. This strategy led to a significant reduction in costs associated with prolonged downtime and structural repairs (e.g., welding), improving overall asset availability.

Nabla recommends ongoing monitoring through periodic NDT (Non-Destructive Testing) inspections using penetrating liquids to track crack development and ensure structural behavior remains within expected margins.

Thanks to this approach, part of the wind farm’s production capacity was recovered, minimizing the economic impact of downtime and providing an effective, safe, and cost-efficient technical solution to a recurring structural problem in this type of wind turbine.

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March and our commitment to a sustainable future

As March begins, we enter a key month for raising awareness about sustainable development and the energy transition. This month is marked by several international days that highlight the critical role of engineering and renewable energy in fighting against climate change. Among them are World Engineering Day for Sustainable Development (March 4), World Energy Efficiency Day (March 5), Climate Day (March 26), and Earth Hour (March 29). Each of these dates highlights the urgent need to reduce our dependence on fossil fuels and embrace sustainable solutions for a cleaner, safer planet for future generations. At the same time, they serve as a reminder and motivation to reinforce our commitment to a greener future.

Leaving “Drill, Baby, Drill” behind, it’s time for change

For decades, the global energy model has been dominated by oil and gas, with policies that encouraged unrestricted exploitation. However, this extractivist mindset is unsustainable and extremely harmful to the planet. The time has come to fully commit to renewable energy sources that can lead us toward a fossil fuel-free future.

At Nabla, we firmly believe in the power of wind energy to reshape the global energy landscape. Our mission is to demonstrate that a renewable-based model is not only viable but the only responsible path to ensuring a sustainable future.

A team committed to driving the energy transition

Engineering is the driving force behind the shift toward a more efficient and sustainable energy model. Thanks to technological advancements and innovation in the wind energy sector, we can extend the lifespan of wind farms, optimize their performance, and reduce the need for new infrastructure. At Nabla, we focus on maximizing the use of existing wind turbines, ensuring they continue generating clean energy for longer and minimizing the environmental impact associated with their replacement.

Energy efficiency and the fight against climate change

Energy efficiency is one of the key pillars in the fight against climate change. Making the most of every unit of energy produced reduces waste and lowers our carbon footprint. Investing in renewable energy and improving energy efficiency is not just an environmental necessity, it is also a smart economic decision that ensures clean energy is accessible to all.

Towards a cleaner planet

The energy transition is a global challenge, but also a great opportunity to change the course of things. This March serves as a reminder of the importance of acting responsibly, supporting initiatives that promote energy efficiency, reduce emissions, and advance sustainable technologies. At Nabla Wind Hub, we remain committed to making wind energy a key pillar in building a cleaner, safer, and more sustainable world for everyone.

What about you? Will you join us?

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Maximizing Wind Turbine Lifespan: Optimization & Maintenance Strategies

Extending the lifespan of wind turbines is essential for enhancing efficiency and reducing operational costs. To achieve this, a combination of preventive maintenance, advanced monitoring systems, and strategic upgrades in wind turbines are key.

In this article, you will find a useful guide on how you can make the most of your asset’s capacity, reducing unnecessary costs:

1. Preventive Maintenance

Regular, scheduled maintenance in wind farms helps to identify and address wear before it leads to major failures. This includes routine inspections, and monitoring for early signs of blade erosion or mechanical fatigue. Preventive measures reduce downtime and improve overall turbine reliability.

2. Monitoring Systems

Nowadays an increasing number of wind turbines are being equipped with condition monitoring systems (CMS) that track critical components like bearings, gearboxes, and electrical systems in real-time. These real-time monitoring systems provide data-driven insights, allowing operators to detect anomalies early and perform targeted interventions, reducing the risk of sudden breakdowns.

3. Upgrades and Retrofits

As turbines age, upgrading certain components can improve efficiency and extend their operational life. Retrofitting advanced control systems, installing more durable blades, or even applying improved retipping solutions can optimize performance and reduce stress on key components.

In Nabla Wind Hub, we are experts in optimizing O&M strategies by its adaptation from a reactive scheme to a site-condition based preventive scheme, implementing preventive solutions fed by high accuracy inputs resulting from our life analysis.

By integrating these strategies, wind farm operators can extend their asset’s lifespan, minimize maintenance costs, and ensure steady, long-term performance, while suppressing the C02 emissions derived from the decommissioning and repowering processes.

Take a look at our O&M engineering here for more information.

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Root cause analysis for structural problems in the rear frames of 2.0 MW wind turbines

Robust design of wind turbine structural components is essential to achieve a life expectancy beyond 20 years. Otherwise, major inspection, maintenance and repair campaigns will be required to meet such target.

There are two fundamental aspects that will influence the design of the component: in the first place, the correct prediction of the loads that affect the wind turbine and, second, an accurate obtaining of the structural response of the system.

Today, we encounter a number of components that, due to inadequate design, suffer structural problems before the 20 year period. An example of such is the rear frame of some 2.0 MW platforms, which often have severe fatigue failures in the rear welds.

The main function of the rear frame is to support the weight of different main components, such as the electrical generator, the transformer or the converter. In addition to this, and due to the accelerations of the nacelle during operation, the rear frame suffers from the inertial forces of the elements that are suspended on it. Furthermore, in some cases, there is the possibility of an eccentricity in the rotor of the electric generator, which can cause a centrifugal force, resulting in a negative effect on the structural integrity of the wind turbine.

For a better understanding of this complex reality, we recommend performing a strength analysis, which first step would consist in obtaining the loads through aeroelastic simulations, considering the specific conditions of the wind farm and the wind turbine operation data.

In the second step of the analysis, a dynamic analysis of the structure is performed. This analysis begins with the development of the Finite Element Model (FEM) of the structure, which requires a reverse engineering process to capture the geometries of the component and assign its physical properties.

Once the model is completed, the modal analysis continues, where the natural frequencies and modes of vibration of the component are identified. These frequencies are compared with the main harmonics of the excitation sources, and it is thanks to this comparison that possible resonance phenomena caused by the accelerations, or the centrifugal force of the generator rotor are identified.

After the dynamic analysis, fatigue analysis is carried out, where a basic analysis based on Von Mises equivalent stress and a more advanced analysis using critical plane-based methodologies are simulated. In our specific case study and after the stress analysis, it is verified that the wind turbine welds are not adequately designed to withstand 20 years of operation.

Thanks to this methodology, the root cause of the component’s fatigue problems is identified, and a possible solution is studied. In this particular case, NWH recommends the installation of certain cross beams and brackets near the welds, stiffening the structure, thus solving the resonance problem, and lowering the stresses in the welds, extending the life of the component up to 20 years or more.

If you want to know more on Root Cause Analysis keep reading in the following link.

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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.

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