Non-Destructive Testing and Condition Monitoring Techniques for Renewable Energy Industrial Assets

By Mayorkinos Papaelias, Fausto Pedro Garcia Marquez and Alexander Karyotakis

Non-Destructive Testing and Condition Monitoring Techniques for Renewable Energy Industrial Assets integrates state-of-the-art information and discusses future developments and their significance to the improvement of the renewable energy industry. Renewable energy assets are complex systems with several critical components that require inspection and adequate maintenance in order to ensure their high availability and uninterrupted operation. This is the first book to apply NDT and condition monitoring to these complex systems.

• Covers inspection and condition monitoring for a broad range of renewable energy systems, including wind turbines, wave energy devices, CSP and photovoltaic plants, and biofuel/biomass power plants
• Includes a review of common types of NDT techniques
• Discusses future developments in NDT and condition monitoring for renewable energy systems

• Language: English
• Publisher: Elsevier Science
• Release date: Sep 4, 2019
• ISBN: 9780128097472

Mayorkinos Papaelias

Mayorkinos Papaelias is a Reader in NDT and Condition Monitoring in the School of Metallogy and Materials at the University of Birmingham, UK. Dr Papaelias leads the research activity in Non-Destructive Testing and Structural Health Condition Monitoring at the Birmingham Railway Centre for Research and Education and conducts research in structural health condition monitoring of wind turbine towers, and advanced condition monitoring of wind turbine gearboxes and rotating machinery. He served as a technical consultant to TWI, ENGITEC, Innovative Technology and Science Ltd, and Instituto de Soldadura e Qualidade. He is editor of two books on fault detection and condition monitoring, and has contributed chapters to books in fault detection and rail inspection. Mayorkinos is chairman of the Education Committee of the International Society for Condition Monitoring of the British Institute of Non-Destructive Testing.

Book preview

Kingdom

Introduction to non-destructive testing and condition monitoring techniques for renewable energy industrial assets

Fausto Pedro García Márqueza; Mayorkinos Papaeliasb; Alexander Karyotakisc, a Ingenium Research Group, University of Castilla-La Mancha, Ciudad Real, Spain, b School of Metallurgy and Materials, The University of Birmingham, Birmingham, United Kingdom, c TERNA ENERGY, Athens, Greece

The economic significance of renewable energy sources has increased profoundly over the last two decades. Renewable energy assets, in the form of wind turbines, photovoltaic installations, tidal turbines, wave energy devices, concentrated solar power plants, biofuel and biomass installations have become important part of the global economy with their net worth value exceeding several hundreds of billions of Euros. Investments in renewable energy are expected to continue to grow until at least 2030, before beginning to stabilise. Renewable energy assets are complex systems with several critical components. Therefore, it is of paramount importance that they are inspected and maintained adequately in order to ensure their high availability and uninterrupted operation. Unexpected failures and faults can result in the underperformance of a particular renewable energy project which may compromise its financial success and endanger future investment. Non-destructive testing (NDT) and condition monitoring should be considered as an integral part of the overall operation of any renewable energy project ensuring its reliable and safe operation and enabling maintenance actions to be carried out effectively and efficiently resulting in significant financial savings for both manufacturers and operators. This book is the first of its kind and will provide a useful insight to industrial engineers and scientists, academics and students in the possibilities that NDT and condition monitoring technologies can offer. It also provides a useful reference to researchers working in the field.

The book has been created for a target audience of engineers and scientists working in renewable energy production, renewable energy asset manufacturing, maintenance and inspection, students and academics in engineering and renewable energy, NDT inspection engineers and researchers across the disciplines of renewable energy, NDT and condition monitoring technologies, offshore engineers and scientists. But it is also open to other readers.

The content of the book is particularly beneficial to its readers who are expected to have a broad and interdisciplinary background, ranging from physicists to mechanical, electrical and civil engineers, metallurgists, materials scientists, computer scientists and IT engineers, mathematicians, and chemists.

At the moment, the information available on NDT and condition monitoring research and applications in renewable energy is very fragmented. This book integrates the state-of-the-art information and discusses the future developments and their significance to the improvement of renewable energy as an industry. The contents of the book are also useful to undergraduate students as well as researchers providing relevant illustrations and other visual paradigms wherever appropriate to enable better absorption of the information contained by the reader.

The literature available on NDT and Condition Monitoring for Renewable Energy sources is very fragmented. Most of the relevant literature sources on the subject can be found in the form of conference and journal papers. This book synthetizes in a single source of literature solely NDT and Condition Monitoring applications and techniques in renewable energy.

The number of wind turbines and their complexity have both increased in recent years. Maintaining a high level of reliability for wind turbines as systems has become gradually significantly more challenging. At the same time, maintenance costs have risen due to the size and complexity of wind turbines even at subcomponent level. The most important faults in wind turbines are those that result in the highest downtime and loss of productivity. There are some studies that have considered specific faults affecting wind turbine operation. However, they depend on the wind turbine model considered, the geographic and environmental changes, etc. Chapter 1 presents a research overview of the main faults commonly affecting industrial wind turbines based on the state-of-the-art together with a systematic analysis. A fault tree has been developed to synthesize all faults of interest and evaluate qualitatively the condition of the wind turbine system. The fault tree has been studied quantitatively via binary decision diagrams. The approach presented in this chapter is a useful study to be implemented in any condition monitoring system in order to support the maintenance management of wind turbines.

Chapter 2 describes the main wind turbine inspection and condition monitoring issues. A general introduction about the importance of the wind turbine industry is done from different market point of view. It is remarked that there is a need for the Operational and Maintenance in this industry and the Levelised Cost of Electricity. It is employed as a remote Condition Monitoring Systems to continuously evaluate the condition of critical wind turbine components. The main objective is to avoid the catastrophic failures. Certain component faults can be particularly dangerous leading even to a complete loss of the wind turbine. A detailed analysis of the main catastrophic failures is introduced in this chapter. In order to avoid them, the main inspections of wind turbine components are described.

Wind energy is also one of the most important renewable energy sources exploited at a global scale with approximately 0.5T W of installed capacity as of 2019. There is a need to optimise the operational and maintenance costs of wind turbines in order to increase the competitiveness of this power generation industry. An efficient way of reducing costs is through an evolution from corrective to predictive maintenance procedures, for example based on condition monitoring of critical turbine components. Condition monitoring systems allow early detection of health degradation of the main components, for example gearbox, brake system, blade, tower, facilitating a proactive response, minimising downtime, and maximising the overall annual capacity production of wind farms. A large number of recent research studies have focused on the field of wind turbine remote condition monitoring due to the importance of operational reliability. Chapter 3 summarises the state-of-the-art in wind turbine maintenance management, describing different maintenance models, condition monitoring techniques, and approaches. A qualitative evaluation, using fault tree analysis, has also been carried out to identify future research opportunities for fault detection and diagnostics.

The weather conditions determine the wind farm energy productivity with time. Ice formation on blades is the environmental phenomenon that generates more downtime in the wind energy industry. Wind turbine operation must stop production when ice is detected on the blades for safety reasons. People, animals, devices, etc., close to the wind farm can be put at risk due to the possibility of ice detaching from the blades as they rotate at high speed. Moreover, abnormal vibration of the wind turbine arising from the ice accumulation can cause failures. The resulting downtime can lead to significant financial costs due to the lost production. NDT techniques are therefore required in order to detect ice accumulation on the blades. Chapter 4 presents the main NDT approaches for blade icing monitoring. The main method for eliminating the ice is also discussed.

Approximately 75% of all wind turbines are based on geared designs. Wind turbine gear designs often follow the ISO 6336-5 standard. Gears are typically made from high Cr steel grades such as 4320, 4820, 9310, and 18CrNiMo7-6. These steel grades have low carbon and high chromium and molybdenum content, to increase the maximum toughness of the material. Wind turbine gearbox designs have been improving over the years resulting in the continuous revision of the IEC-61400 international standard, which outlines the minimum requirements for specification, design, and verification of gearboxes in wind turbines. Despite these continuous improvements, several technical challenges remain that have yet to be overcome, especially in the case of offshore wind farms. Chapter 5 covers the most common wind turbine gearbox failures, while also providing examples on how to detect and prevent unexpected failures by using appropriate condition monitoring systems and surface engineering treatment techniques, respectively.

Turbulence influences the amount of wind energy harvested using wind turbine blades reducing the efficiency of the overall electric power production of wind turbines. This results to a lower level of competitiveness of this industry in comparison with other energy sources such as fossil fuel-based power generation. Turbulence effects can be further enhanced by the characteristics of the wind turbine blade surface itself, for example ice accumulation, impacting insects, dirt, mud. NDT techniques can be applied in order to monitor the blade surface characteristics or condition. However, NDT is yet to be widely employed for this particular purpose in the industry yet. Chapter 6 looks into the application of ultrasonic waves for monitoring the presence of dirt, mud, and other potential surface artefacts potentially accumulating with time. Several scenarios have been considered in order to validate this particular approach, considering various levels of mud. Pattern recognition employing neural networks has been considered for the detection and quantification of accumulation of mud on the blade surface.

Solar plants require sophisticated condition monitoring systems and methods to manage the new large power production due to the increasing number of photovoltaics modules installed. Chapter 7 focuses on thermographic techniques for the evaluation of solar panels. Thermography can be used to evaluate the condition of the photovoltaic system very fast, and economically providing reliable inspection results. The most important thermographic techniques for solar plants are discussed herewith together with the governing principles. Active and passive techniques are analysed in order to determine the method that provides the best results. The main advantages and disadvantages of using thermographic technologies are analysed. In addition, the main variables that should be considered during thermographic inspection are considered. Finally, certain types of failures that can be detected using thermography are evaluated through the different thermographic patterns in obtained thermal images.

The constant increasing of renewable energy demand is leading wind turbines to become very complex and sophisticated devices. These technological developments imply new methods and tools to ensure the reliability of the systems. For this purpose, non-destructive testing techniques are widely employed in the field of wind turbine maintenance. Chapter 8 presents the implementation of a walking robot-based system that allows non-destructive testing to be carried out in difficult access areas of wind turbines. The chapter is divided as a brief literature overview that is done to identify those limitations of current procedures that could be overcome by using the proposed tool; a detailed explanation of the novel system is given, where the different components and features of the robot are described; several applications of the proposed systems are also shown. These applications can be classified according to the type of sensor and the area to inspect: Acoustic emission, visual inspection, guided wave testing, noise analysis, or thermographic inspections are some of the non-destructive testing techniques that can be aided. Moreover, external and internal surfaces of blades, tower, nacelle, and other difficult access areas can be reached by the robot. Finally, some advantages of this system are enhanced with respect to the conventional methodologies. The usefulness of the proposed system is demonstrated in terms of safety and efficiency with respect to other procedures.

The development of newer and more ecofriendly energies is now more important in the world. Solar energy has been growing considerably over the last years, and, for example, photovoltaic solar farms size has increased, where the problems in operation and maintenance also has raised. Automated inspection is being applied with emerging hardware and software technologies such as computer vision, unmanned aerial vehicles, and thermal cameras. Chapter 9 illustrates an integration of all these technologies, coming up with an effective solution for the detection of malfunctioning solar panels in large solar parks.

Tidal energy is still a developing renewable energy source with only a few commercial projects having been commissioned to date. Although there are several different device designs that have been proposed and investigated for harvesting tidal energy, most of them have only been tested either at model or small scale. A handful of designs have managed to gather sufficient financial support to be tested at sea at full scale. There are currently plans for significant utility-sized tidal energy plants in the short-to-medium term. Nonetheless, these still face uncertainty regarding their eventual implementation due to financing issues that have not been entirely resolved yet. Types of damage that can affect the drive-train of a tidal turbine include misalignment, imbalance, looseness, broken gear teeth, bearing defects, lubrication variability resulting in dry contact of the rotating surfaces, and excessive wear. It is very important to be able to detect accidental impacts on the rotor and damage evolution in the drive-train. Certain commercial tidal turbines make use of vibration condition monitoring systems in the same way as most multi-MW wind turbines. Chapter 10 presents the main tidal power generator components: rotor blades, drive train, power convertors, low-voltage consumable power, control and management systems, support structure, and power transmission. The main condition monitoring system for each component are discussed.

Acoustic emission testing is a structural health monitoring technique with a wide range of applications. Several structural components in various renewable energy systems, for example wind turbine blades made of fibre reinforced plastics, towers, foundation, tidal turbine blades, wave energy harvesting systems, pressure vessels in concentrated solar power plants and many others, can be monitored using acoustic emission. Acoustic emission measurements can produce datasets which contain thousands to hundreds of thousands of logged signals. Particularly for large components, such as a wind turbine blade, where several piezoelectric acoustic emission sensors are required to monitor the load bearing parts of the structure over a prolonged time period, the size of the dataset generated may be exceedingly large. Although manual analysis of large acoustic emission datasets is possible, it is not trivial, particularly when complex damage mechanics are involved. Therefore, it is desirable to use methods to automatically analyse complex acoustic emission datasets without the need for manual intervention. Effective automatic analysis can also help establish appropriate filtering methodologies which can help improve data acquisition parameters, so as to minimise the logging of unwanted signals from noise sources such as friction and echoes of primary damage events. The automatic processing of large acoustic emission datasets can be based on statistical analysis using different algorithms. Chapter 11 summarises the various algorithms that can be used for the unsupervised clustering of complex acoustic emission